890 lines
28 KiB
HTML
890 lines
28 KiB
HTML
<!DOCTYPE html>
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<html lang="en">
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<head>
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<meta charset="UTF-8">
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<meta name="viewport" content="width=device-width, initial-scale=1.0">
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<title>CTF Write-up: Heap Exploitation in glibc 2.35 | River Rooks</title>
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<style>
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@import url('https://fonts.googleapis.com/css2?family=IBM+Plex+Mono:ital,wght@0,400;0,500;0,700;1,400&family=Inter:ital,wght@0,400;0,500;0,700;1,400&family=JetBrains+Mono:ital,wght@0,400;0,500;1,400&display=swap');
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:root {
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--bg-canvas: #0d0f12; /* Deep slate/charcoal canvas */
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--bg-surface: #121417; /* Tile surface */
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--bg-elevated: #1c1f26; /* Hovered surface */
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--border-color: #2b303b; /* Crisp 1px border */
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--text-primary: #e0e6f0; /* Light off-white prose */
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--text-muted: #8a95a5; /* Monospace metadata */
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--accent-cyan: #00f0ff; /* Active accent */
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--accent-green: #00e676; /* Success / online */
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--accent-amber: #ffb700; /* Warning / highlight */
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--accent-red: #ff5252; /* Critical alert */
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}
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* {
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box-sizing: border-box;
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margin: 0;
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padding: 0;
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}
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body {
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background-color: var(--bg-canvas);
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color: var(--text-primary);
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font-family: 'Inter', sans-serif;
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line-height: 1.7;
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min-height: 100vh;
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display: flex;
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flex-direction: column;
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align-items: center;
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padding: 24px 16px 48px 16px;
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}
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.tiling-layout {
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width: 100%;
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max-width: 1160px;
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display: flex;
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flex-direction: column;
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gap: 16px;
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}
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/* Top Global Header Bar (Gateway 3 Standard) */
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.global-bar {
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background-color: var(--bg-surface);
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border: 1px solid var(--border-color);
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border-radius: 4px;
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padding: 10px 18px;
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display: flex;
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justify-content: space-between;
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align-items: center;
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font-family: 'IBM Plex Mono', monospace;
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font-size: 0.8rem;
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flex-wrap: wrap;
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gap: 10px;
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}
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.brand-group {
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display: flex;
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align-items: center;
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gap: 10px;
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color: var(--text-primary);
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font-weight: 700;
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}
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.status-indicator {
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width: 8px;
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height: 8px;
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background-color: var(--accent-green);
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display: inline-block;
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}
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.bar-nav {
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display: flex;
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gap: 14px;
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align-items: center;
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}
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.bar-link {
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color: var(--text-muted);
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text-decoration: none;
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transition: none;
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}
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.bar-link:hover {
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color: var(--accent-cyan);
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}
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/* Article Workspace: 2-Column Split (Sidebar on Left) */
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.article-workspace-grid {
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display: grid;
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grid-template-columns: 290px 1fr;
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gap: 16px;
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align-items: start;
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}
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@media (max-width: 960px) {
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.article-workspace-grid {
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grid-template-columns: 1fr;
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}
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}
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/* Left Sidebar */
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.article-sidebar {
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display: flex;
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flex-direction: column;
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gap: 16px;
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position: sticky;
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top: 16px;
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}
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.sidebar-tile {
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background-color: var(--bg-surface);
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border: 1px solid var(--border-color);
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border-radius: 4px;
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padding: 18px;
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display: flex;
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flex-direction: column;
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gap: 12px;
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}
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.sidebar-heading {
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font-family: 'IBM Plex Mono', monospace;
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font-size: 0.82rem;
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font-weight: 700;
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color: var(--text-muted);
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text-transform: uppercase;
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letter-spacing: 0.05em;
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border-bottom: 1px solid var(--border-color);
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padding-bottom: 8px;
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display: flex;
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justify-content: space-between;
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align-items: center;
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}
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.toc-nav {
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display: flex;
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flex-direction: column;
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gap: 4px;
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font-family: 'IBM Plex Mono', monospace;
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font-size: 0.78rem;
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}
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.toc-link {
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color: var(--text-muted);
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text-decoration: none;
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padding: 4px 6px;
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border-radius: 2px;
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transition: none;
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line-height: 1.4;
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display: block;
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}
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.toc-link:hover {
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background-color: var(--bg-elevated);
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color: var(--accent-cyan);
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}
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.toc-link.active {
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color: var(--accent-cyan);
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background-color: var(--bg-canvas);
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border-left: 2px solid var(--accent-cyan);
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font-weight: 700;
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}
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.toc-sub {
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padding-left: 14px;
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color: var(--text-muted);
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font-size: 0.74rem;
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}
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/* Collapsible Menu */
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.collapsible-drawer {
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border: 1px solid var(--border-color);
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border-radius: 3px;
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background-color: var(--bg-canvas);
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overflow: hidden;
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}
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.collapsible-summary {
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background-color: var(--bg-elevated);
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padding: 8px 12px;
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font-family: 'IBM Plex Mono', monospace;
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font-size: 0.76rem;
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font-weight: 700;
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color: var(--text-primary);
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cursor: pointer;
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list-style: none;
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display: flex;
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justify-content: space-between;
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align-items: center;
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user-select: none;
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}
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.collapsible-summary::-webkit-details-marker {
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display: none;
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}
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.collapsible-summary::after {
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content: "[+]";
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color: var(--accent-cyan);
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font-weight: 700;
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}
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.collapsible-drawer[open] .collapsible-summary::after {
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content: "[-]";
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}
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.drawer-content {
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padding: 10px;
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display: flex;
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flex-direction: column;
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gap: 8px;
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}
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.related-card {
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background-color: var(--bg-surface);
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border: 1px solid var(--border-color);
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border-radius: 2px;
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padding: 8px 10px;
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text-decoration: none;
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display: flex;
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flex-direction: column;
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gap: 3px;
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transition: none;
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}
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.related-card:hover {
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border-color: var(--accent-cyan);
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background-color: var(--bg-elevated);
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}
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.related-date {
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font-family: 'IBM Plex Mono', monospace;
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font-size: 0.7rem;
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color: var(--accent-cyan);
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}
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.related-title {
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font-family: 'IBM Plex Mono', monospace;
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font-size: 0.8rem;
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font-weight: 700;
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color: var(--text-primary);
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line-height: 1.35;
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}
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.related-card:hover .related-title {
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color: var(--accent-cyan);
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}
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/* Main Article Tile */
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.article-tile {
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background-color: var(--bg-surface);
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border: 1px solid var(--border-color);
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border-radius: 4px;
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padding: 36px 40px;
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display: flex;
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flex-direction: column;
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gap: 24px;
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}
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@media (max-width: 600px) {
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.article-tile {
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padding: 24px 18px;
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}
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}
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.article-header-block {
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border-bottom: 1px solid var(--border-color);
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padding-bottom: 24px;
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display: flex;
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flex-direction: column;
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gap: 12px;
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}
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.article-breadcrumbs {
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font-family: 'IBM Plex Mono', monospace;
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font-size: 0.78rem;
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color: var(--text-muted);
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display: flex;
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align-items: center;
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gap: 8px;
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}
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.article-main-title {
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font-family: 'IBM Plex Mono', monospace;
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font-size: 2.3rem;
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font-weight: 700;
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color: var(--text-primary);
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letter-spacing: -0.02em;
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line-height: 1.25;
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}
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@media (max-width: 768px) {
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.article-main-title {
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font-size: 1.8rem;
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}
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}
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.article-meta-row {
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display: flex;
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flex-wrap: wrap;
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align-items: center;
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gap: 14px;
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font-family: 'IBM Plex Mono', monospace;
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font-size: 0.8rem;
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color: var(--text-muted);
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}
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.tag-chip {
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background-color: var(--bg-canvas);
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border: 1px solid var(--border-color);
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padding: 2px 6px;
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border-radius: 2px;
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color: var(--text-muted);
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}
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/* Markdown Body */
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.markdown-prose {
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max-width: 68ch;
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font-size: 1.02rem;
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color: var(--text-primary);
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line-height: 1.7;
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}
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.markdown-prose p {
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margin-bottom: 18px;
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}
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.markdown-prose h2 {
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font-family: 'IBM Plex Mono', monospace;
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font-size: 1.45rem;
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font-weight: 700;
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color: var(--text-primary);
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margin: 36px 0 16px 0;
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padding-bottom: 8px;
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border-bottom: 1px solid var(--border-color);
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}
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.markdown-prose h3 {
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font-family: 'IBM Plex Mono', monospace;
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font-size: 1.15rem;
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font-weight: 700;
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color: var(--text-primary);
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margin: 28px 0 12px 0;
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}
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.markdown-prose code:not(pre code) {
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font-family: 'JetBrains Mono', monospace;
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font-size: 0.88rem;
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background-color: var(--bg-canvas);
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border: 1px solid var(--border-color);
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padding: 2px 6px;
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border-radius: 3px;
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color: var(--accent-cyan);
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}
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/* Mathematical / Algorithm Formula Box */
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.formula-card {
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background-color: var(--bg-canvas);
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border: 1px solid var(--border-color);
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border-left: 3px solid var(--accent-cyan);
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border-radius: 3px;
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padding: 14px 18px;
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margin: 20px 0;
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font-family: 'JetBrains Mono', monospace;
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font-size: 0.88rem;
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line-height: 1.6;
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}
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.formula-title {
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font-family: 'IBM Plex Mono', monospace;
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font-size: 0.76rem;
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color: var(--text-muted);
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text-transform: uppercase;
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margin-bottom: 6px;
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}
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/* Code Block Containers */
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.code-block-container {
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margin: 22px 0;
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border: 1px solid var(--border-color);
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border-radius: 4px;
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background-color: var(--bg-canvas);
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overflow: hidden;
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}
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.code-block-header {
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background-color: var(--bg-surface);
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border-bottom: 1px solid var(--border-color);
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padding: 6px 14px;
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display: flex;
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justify-content: space-between;
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align-items: center;
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font-family: 'IBM Plex Mono', monospace;
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font-size: 0.74rem;
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color: var(--text-muted);
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}
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.copy-btn {
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background: transparent;
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border: 1px solid var(--border-color);
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color: var(--text-muted);
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padding: 2px 8px;
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font-family: inherit;
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font-size: 0.72rem;
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cursor: pointer;
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border-radius: 2px;
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transition: none;
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}
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.copy-btn:hover {
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border-color: var(--accent-cyan);
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color: var(--accent-cyan);
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}
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.code-block-container pre {
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padding: 14px 16px;
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overflow-x: auto;
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font-family: 'JetBrains Mono', monospace;
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font-size: 0.82rem;
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line-height: 1.5;
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color: var(--text-primary);
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}
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/* GitHub-style Alerts */
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.markdown-callout {
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margin: 20px 0;
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padding: 14px 18px;
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border-radius: 3px;
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border: 1px solid var(--border-color);
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background-color: var(--bg-canvas);
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font-size: 0.94rem;
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line-height: 1.6;
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}
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.callout-caution {
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border-left: 4px solid var(--accent-red);
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}
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.callout-note {
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border-left: 4px solid var(--accent-cyan);
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}
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.callout-title {
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font-family: 'IBM Plex Mono', monospace;
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font-weight: 700;
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font-size: 0.82rem;
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margin-bottom: 6px;
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display: flex;
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align-items: center;
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gap: 6px;
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}
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.callout-caution .callout-title { color: var(--accent-red); }
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.callout-note .callout-title { color: var(--accent-cyan); }
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/* Tables */
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.table-container {
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width: 100%;
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overflow-x: auto;
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margin: 22px 0;
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}
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.markdown-table {
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width: 100%;
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border-collapse: collapse;
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font-size: 0.84rem;
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font-family: 'IBM Plex Mono', monospace;
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text-align: left;
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}
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.markdown-table th {
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background-color: var(--bg-canvas);
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border: 1px solid var(--border-color);
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padding: 8px 12px;
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color: var(--text-muted);
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font-weight: 700;
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}
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.markdown-table td {
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border: 1px solid var(--border-color);
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padding: 8px 12px;
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color: var(--text-primary);
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}
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|
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/* Footnotes Section */
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.footnotes-section {
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margin-top: 36px;
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padding-top: 20px;
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border-top: 1px solid var(--border-color);
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font-size: 0.84rem;
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color: var(--text-muted);
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}
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.footnote-item {
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margin-bottom: 8px;
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}
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/* Global Footer Tile (Gateway 3 Exact Match) */
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.footer-tile {
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background-color: var(--bg-surface);
|
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border: 1px solid var(--border-color);
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border-radius: 4px;
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padding: 12px 20px;
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display: flex;
|
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justify-content: space-between;
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align-items: center;
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font-family: 'IBM Plex Mono', monospace;
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font-size: 0.78rem;
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color: var(--text-muted);
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flex-wrap: wrap;
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gap: 10px;
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}
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.footer-links-cluster {
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display: flex;
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gap: 12px;
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align-items: center;
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}
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.footer-btn {
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color: var(--text-primary);
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text-decoration: none;
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padding: 2px 4px;
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transition: none;
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}
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.footer-btn:hover {
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background-color: var(--accent-cyan);
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color: var(--bg-canvas);
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}
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.pipe {
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color: var(--border-color);
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}
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</style>
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</head>
|
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<body>
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|
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<main class="tiling-layout">
|
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|
|
<!-- Top Global Header Bar (Gateway 3 Standard) -->
|
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<header class="global-bar">
|
|
<div class="brand-group">
|
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<span class="status-indicator"></span>
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<span>RIVER ROOKS // CTF EXPLOITATION ARCHIVE</span>
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</div>
|
|
<nav class="bar-nav" aria-label="Navigation">
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<a href="service-gateway-tiling.html" class="bar-link">Gateway 3 ↗</a>
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<a href="blog-tiling-lead.html" class="bar-link">← Back to Blog Feed</a>
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<a href="https://git.rooks.dev" target="_blank" rel="noopener" class="bar-link">Git Forge</a>
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<a href="feed.xml" class="bar-link">RSS</a>
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<a href="index.html" class="bar-link">Catalog ↗</a>
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</nav>
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</header>
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|
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<!-- Main Workspace: Sidebar TOC + Reading Canvas -->
|
|
<div class="article-workspace-grid">
|
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|
|
<!-- Left Sidebar: Document Outline + Collapsible Series -->
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<div class="sidebar-heading">
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<span>DOCUMENT OUTLINE</span>
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<span style="color: var(--accent-cyan);">INDEX</span>
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</div>
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<nav class="toc-nav" aria-label="Table of Contents">
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<a href="#challenge-intro" class="toc-link active">> 1.0 Challenge Synopsis</a>
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<a href="#safe-linking" class="toc-link">> 2.0 Safe-Linking Pointer Mangling</a>
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<a href="#mangling-math" class="toc-link toc-sub">2.1 Mathematical Derivation</a>
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<a href="#gdb-session" class="toc-link">> 3.0 GDB Memory Inspection</a>
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<a href="#house-of-apple" class="toc-link">> 4.0 House of Apple Hijacking</a>
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<a href="#mitigation-matrix" class="toc-link">> 5.0 Mitigation History</a>
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<a href="#footnotes" class="toc-link">> 6.0 References & Notes</a>
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<span>SECURITY REPOSITORY</span>
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<span>DRAWER</span>
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</div>
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<details class="collapsible-drawer" open>
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<summary class="collapsible-summary">
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<span>Security Dispatches (3)</span>
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</summary>
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<div class="drawer-content">
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<a href="article-tiling-firmware.html" class="related-card">
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<span class="related-date">2026-07-20 • 8 min</span>
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<span class="related-title">Reverse Engineering IoT Firmware: SPI Flash</span>
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<span style="color: var(--text-muted); font-size: 0.7rem;">[#firmware] [#hardware]</span>
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</a>
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<a href="article-tiling-traefik.html" class="related-card">
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<span class="related-date">2026-07-15 • 12 min</span>
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<span class="related-title">High-Availability Traefik Router with Docker</span>
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<span style="color: var(--text-muted); font-size: 0.7rem;">[#homelab] [#networking]</span>
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</a>
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<a href="blog-tiling-lead.html" class="related-card">
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<span class="related-date">2026-07-10 • 6 min</span>
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<span class="related-title">POSIX sh vs. Bash: Portability in Modern Scripts</span>
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<span style="color: var(--text-muted); font-size: 0.7rem;">[#posix-sh] [#unix]</span>
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</a>
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</div>
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</details>
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</div>
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<div style="display: flex; justify-content: space-between; margin-bottom: 6px;">
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<span>ALLOCATOR:</span>
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<span style="color: var(--accent-cyan); font-weight: 700;">GLIBC 2.35-0UBUNTU3</span>
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</div>
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<div style="display: flex; justify-content: space-between; margin-bottom: 6px;">
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<span>EXPLOIT PRIMITIVE:</span>
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<span style="color: var(--accent-amber); font-weight: 700;">TCACHE POISONING</span>
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</div>
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<div style="display: flex; justify-content: space-between;">
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<span>TARGET HOOK:</span>
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<span style="color: var(--accent-green);">_IO_FILE VTABLE</span>
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</div>
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</div>
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<header class="article-header-block">
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<div class="article-breadcrumbs">
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<span>~/notes/</span>
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<span>></span>
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<span style="color: var(--accent-cyan);">ctf-heap-glibc-2-35.md</span>
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</div>
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<h1 class="article-main-title">CTF Write-up: Heap Exploitation in glibc 2.35</h1>
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<div class="article-meta-row">
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<div><span style="color: var(--accent-cyan);">2026-06-28</span></div>
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<span>•</span>
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<div><span>15 MIN READ</span></div>
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<span>•</span>
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<div><span>AUTHOR: RIVER ROOKS</span></div>
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<span>•</span>
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<div>
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<span class="tag-chip">[#ctf]</span>
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<span class="tag-chip">[#binary-exploitation]</span>
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<span class="tag-chip">[#security]</span>
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<span class="tag-chip">[#glibc]</span>
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</div>
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</div>
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</header>
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<!-- Markdown Prose Content -->
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<div class="markdown-prose">
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<h2 id="challenge-intro">1.0 Challenge Synopsis</h2>
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<p>
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During the DEFCON qualifier challenges, our team encountered a hardened 64-bit Linux binary linked against <code>glibc 2.35</code>. Standard legacy heap exploitation techniques—such as poisoning <code>__malloc_hook</code> or <code>__free_hook</code>—are rendered obsolete because upstream glibc maintainers removed all allocation hook pointer symbols entirely in version 2.34.
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</p>
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<p>
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This write-up covers breaking modern <strong>tcache safe-linking pointer mangling</strong> and redirecting execution control flow using the <strong>House of Apple 2</strong> technique against the wide character vtable pointers inside <code>_IO_FILE</code> structures.
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</p>
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<h2 id="safe-linking">2.0 Safe-Linking Pointer Mangling</h2>
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<p>
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Introduced in glibc 2.32, safe-linking protects single-linked singly linked list pointers (such as entries inside the Thread Local Cache <code>tcache</code> and fastbins) against off-by-one overwrites and UAF corruption.
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</p>
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<h3 id="mangling-math">2.1 Mathematical Derivation</h3>
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<div class="formula-card">
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<div class="formula-title">POINTER MANGLING FORMULA</div>
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<div>Mangled_Pointer (P') = (Address_of_Chunk >> 12) ^ Target_Pointer (P)</div>
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</div>
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<p>
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Since the lowest 12 bits of <code>Address_of_Chunk >> 12</code> are randomized by ASLR, overwriting <code>P'</code> directly without an address leak causes the kernel to dereference invalid virtual memory pages, aborting with <code>SIGSEGV</code>.
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</p>
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<p>
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However, when an arbitrary read primitive leaks the mangled value of the terminal chunk in the tcache bin (where <code>Target_Pointer = NULL</code>), the equation simplifies:
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</p>
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<div class="formula-card">
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<div>Leaked_Mangled = (Chunk_Addr >> 12) ^ 0x0 ==> ASLR_Key = Leaked_Mangled</div>
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</div>
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<div class="markdown-callout callout-caution">
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<div class="callout-title">[!CAUTION] Pointer Alignment Constraints</div>
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<p>
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In glibc 2.35, chunks inserted into tcache bins must also adhere to strict 16-byte address alignment. Forging a fake chunk unaligned to a 16-byte boundary triggers <code>malloc(): unaligned tcache chunk detected</code> aborts.
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</p>
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</div>
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<h2 id="gdb-session">3.0 GDB Memory Inspection</h2>
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<p>
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Attaching GDB with the <code>pwndbg</code> extension confirms the tcache bin layout and reveals the mangled pointer representation in memory:
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</p>
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<div class="code-block-header">
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<div class="code-title">
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<span>gdb-pwndbg stdout: heap inspection</span>
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<span>GDB</span>
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</div>
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<button class="copy-btn" onclick="copySnippet(this)">Copy GDB</button>
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<pre><code>pwndbg> tcachebins
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tcachebins
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0x40 [ 2]: 0x55555555a2a0 → 0x55555555a260
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pwndbg> x/4gx 0x55555555a2a0
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0x55555555a2a0: 0x0000555555550730 0x0000000000000000
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0x55555555a2b0: 0x0000000000000000 0x0000000000000041
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pwndbg> tele 0x55555555a2a0
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00:0000 │ 0x55555555a2a0 → 0x555555550730 (MANGLED POINTER: 0x55555555a260 ^ (0x55555555a >> 12))</code></pre>
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</div>
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<h2 id="house-of-apple">4.0 House of Apple Hijacking</h2>
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<p>
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With the ability to allocate chunks onto arbitrary memory addresses via tcache poisoning, we target <code>_IO_list_all</code>. When <code>exit()</code> or <code>abort()</code> is invoked by the runtime, the glibc standard I/O cleanup routine iterates through the <code>_IO_FILE</code> linked list and invokes <code>_IO_wfile_overflow()</code>:
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<span>house_of_apple_payload.c</span>
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<span>C99</span>
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<pre><code>// Constructing fake _IO_FILE_plus structure
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struct _IO_FILE_plus *fake_file = (struct _IO_FILE_plus *)payload;
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fake_file->file._flags = 0x6873; // "sh" in ASCII
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fake_file->file._mode = 1; // Force wide character stream mode
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fake_file->vtable = (const struct _IO_jump_t *)wide_vtable_addr;
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// Trigger call to system("/bin/sh") on stream flush
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fake_file->file._wide_data->_wide_vtable->doallocate = (void *)system_addr;</code></pre>
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</div>
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<h2 id="mitigation-matrix">5.0 Glibc Heap Mitigation History</h2>
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<p>
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Tracking defensive hardening milestones across recent glibc releases:
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</p>
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<div class="table-container">
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<table class="markdown-table">
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<thead>
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<tr>
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<th>glibc Version</th>
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<th>Defensive Mitigation Added</th>
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<th>Status</th>
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<th>Impact on Attackers</th>
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</tr>
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</thead>
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<tbody>
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<tr>
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<td><code>2.26</code></td>
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<td>Thread Cache (tcache) introduced</td>
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<td>Active</td>
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<td>Initially lacked double-free and count sanity checks.</td>
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</tr>
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<tr>
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<td><code>2.29</code></td>
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<td>tcache double-free check (key field)</td>
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<td>Active</td>
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<td>Stores pointer to tcache struct in chunk data.</td>
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</tr>
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<tr>
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<td><code>2.32</code></td>
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<td>Safe-Linking Pointer Mangling</td>
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<td>Hardened</td>
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<td>Requires ASLR heap base leak to forge pointers.</td>
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</tr>
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<tr>
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<td><code>2.34</code></td>
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<td>Removal of <code>__malloc_hook</code> / <code>__free_hook</code></td>
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<td>Enforced</td>
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<td>Forces targeting of <code>_IO_FILE</code> and stack frames.</td>
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</tr>
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<tr>
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<td><code>2.35</code></td>
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<td>Alignment verification on tcache chunks</td>
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<td>Enforced</td>
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<td>Eliminates misaligned chunk allocations entirely.</td>
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</tbody>
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</table>
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</div>
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<div class="footnotes-section" id="footnotes">
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<div class="footnote-item">
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<sup>[1]</sup> Safe-Linking was first proposed by Eyal Itkin for memory allocators in modern operating systems.
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</div>
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<div class="footnote-item">
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<sup>[2]</sup> House of Apple exploitation methodology authored by roderickchan, targeting wide character I/O functions.
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</div>
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</div>
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