Browser Exploitation Skill for Claude

Browser & Client-Side Exploitation

Turn a single client-side bug into full host compromise. The modern browser is a chain target: a JS-engine bug yields an in-renderer arbitrary read/write, the V8 heap sandbox must be escaped to get a native R/W, then a second logic/memory bug in a privileged process (browser broker, GPU) escapes the OS sandbox. Electron and embedded webviews collapse several of these steps. Every cluster pairs the offensive primitive with renderer-crash/IPC telemetry, Sigma/EDR detection, and cleanup OPSEC.

When to Activate

• A V8/JavaScriptCore bug (type confusion, OOB, UAF, JIT mis-speculation) must become addrof/fakeobj and an in-renderer arbitrary R/W.
• An in-renderer R/W exists but is trapped inside the V8 heap sandbox (pointer compression) and needs a trusted-pointer / Wasm-object escape to native memory.
• A renderer is fully compromised and you need to escape the OS sandbox via Mojo IPC handle/logic bugs or the GPU process (Dawn/WebGPU, ANGLE).
• Auditing or exploiting an Electron / CEF / WebView2 app: contextIsolation/nodeIntegration/sandbox misconfig, preload-bridge & IPC abuse, ASAR/fuse/snapshot tampering.
• Assembling a 1-click drive-by RCE chain (renderer → sandbox escape → host) for an authorized red-team delivery, or doing cross-engine (Safari/JSC) work.
• Patch-diffing a Chrome/V8/WebKit security release to build an n-day client-side exploit.

Technique Map

| Technique | ATT&CK | CWE | Reference | Script |

|-----------|--------|-----|-----------|--------|

| JIT type confusion (TurboFan/Maglev/Turboshaft) | T1203 | CWE-843 | references/v8-jit-typeconfusion.md | scripts/v8_typer.js |

| Element-kind confusion -> addrof/fakeobj | T1203 | CWE-843 | references/v8-jit-typeconfusion.md | scripts/v8_typer.js |

| OOB read/write on JSArray/TypedArray | T1203 | CWE-787 | references/v8-jit-typeconfusion.md | scripts/v8_typer.js |

| In-renderer arbitrary R/W (fake TypedArray) | T1203 | CWE-787 | references/v8-jit-typeconfusion.md | scripts/v8_typer.js |

| V8 heap-sandbox escape via raw Wasm pointer | T1203 | CWE-787 | references/v8-sandbox-escape.md | scripts/sandbox_escape.js |

| Trusted Pointer Table / WasmExportedFunctionData abuse | T1203 | CWE-843 | references/v8-sandbox-escape.md | scripts/sandbox_escape.js |

| Code/exec via Wasm JIT region pivot | T1203 | CWE-94 | references/v8-sandbox-escape.md | scripts/sandbox_escape.js |

| Mojo IPC handle-confusion sandbox escape | T1203 | CWE-269 | references/renderer-to-browser-escape.md | scripts/mojo_fuzz_harness.py |

| GPU-process UAF/OOB (Dawn/WebGPU, ANGLE) | T1203 | CWE-416 | references/renderer-to-browser-escape.md | scripts/mojo_fuzz_harness.py |

| Mojo interface fuzzing for broker bugs | T1203 | CWE-20 | references/renderer-to-browser-escape.md | scripts/mojo_fuzz_harness.py |

| Electron contextIsolation/IPC bridge RCE | T1059.007 | CWE-1188 | references/electron-webview-rce.md | scripts/electron_audit.py |

| nodeIntegration / webviewTag preload abuse | T1059.007 | CWE-829 | references/electron-webview-rce.md | scripts/electron_audit.py |

| ASAR integrity / fuse / V8 snapshot tamper | T1574.002 | CWE-345 | references/electron-webview-rce.md | scripts/electron_audit.py |

| XSS/open-redirect -> Electron RCE | T1189 | CWE-79 | references/electron-webview-rce.md | scripts/electron_audit.py |

| 1-click drive-by chain delivery | T1189 | CWE-693 | references/clientside-rce-chains.md | scripts/chain_server.py |

| Cross-engine (JSC/WebKit) primitive port | T1203 | CWE-843 | references/clientside-rce-chains.md | scripts/chain_server.py |

Quick Start

# 0. Pin the exact target build (Chrome/Edge/Electron all carry a V8 version)
#    chrome://version  | edge://version  | electron --version
jsvu --engines=v8                                   # local d8 of matching version
./scripts/d8_debug.sh ./d8 ./poc.js                 # d8 w/ exploit-friendly flags

# 1. Engine bug -> in-renderer R/W  (see references/v8-jit-typeconfusion.md)
d8 --allow-natives-syntax --shell ./scripts/v8_typer.js
#   yields addrof(), fakeobj(), read64()/write64() inside the V8 heap cage

# 2. Escape the V8 heap sandbox -> native R/W  (references/v8-sandbox-escape.md)
d8 --no-sandbox-testing-mode ./scripts/sandbox_escape.js   # local test;
#   on a real build: abuse trusted Wasm object raw pointer -> overwrite RWX Wasm code

# 3. Escape the OS sandbox: Mojo broker logic bug OR GPU-process memory bug
python3 scripts/mojo_fuzz_harness.py --interface FileSystemAccess --iters 100000

# 4. Electron / webview target: audit + weaponize
python3 scripts/electron_audit.py /path/to/app.asar      # finds nodeIntegration/IPC/fuse gaps
#   craft IPC/preload payload from the report; package XSS->RCE

# 5. Stage the full 1-click chain and serve it
python3 scripts/chain_server.py --stage1 renderer.js --stage2 escape.js --lhost 10.0.0.5 --lport 8080

OPSEC & Detection (summary)

| Technique | Telemetry/IOC | Detection (Sigma/EDR) | OPSEC note |

|-----------|---------------|-----------------------|------------|

| JIT type confusion | Renderer crash dumps (chrome_crashpad, crashpad_handler), GPU/renderer restarts, *-crash in ~/AppData/Local/.../Crashpad | Sigma: spike in renderer crash reports; EDR on crashpad_handler bursts | Spray/clean up corrupted arrays; bail without crashing on failed type-check; do not leave %DebugPrint calls |

| V8 sandbox escape | Native R/W faults if math is off; abnormal RWX Wasm pages | EDR: RWX region churn inside chrome.exe/renderer; ETW VirtualProtect to RWX | Keep corruption inside the cage until the last step; reuse existing RWX Wasm code page rather than allocating new |

| Mojo broker escape | Browser process spawning cmd.exe/powershell.exe/rundll32.exe; unexpected file writes by broker | Sigma: chrome.exe/msedge.exe parent -> shell child; EDR child-process rule; Mojo message audit | Live off the broker's own capabilities (file write, process launch); avoid spawning a console child — inject instead |

| GPU-process bug | GPU process crashes (--type=gpu), Dawn/ANGLE asserts, DXGI/Metal faults | EDR on GPU-process child anomalies; WebGPU enabled via policy = surface | Test against the right GPU backend (D3D11/Metal/Vulkan); fail closed without crashing the GPU process |

| Electron IPC/preload RCE | app.asar mtime change, node child of Electron app, child_process.exec | Sigma: Electron app spawning shells; FIM on app.asar/snapshot blobs | Prefer in-process JS exec (require gadget) over child_process; restore app.asar mtime after fuse/snapshot tamper |

| Drive-by chain delivery | Suspicious text/html with large encoded JS, WebSocket/long-poll to attacker host, UA-gated content | Proxy/Sigma on long base64/%u blobs in HTML; JA3/JA4 of staging host | UA/feature gate so only the exact target build receives stage-2; single-use, expiring URLs |

Deep Dives

• references/v8-jit-typeconfusion.md — V8 object model, Map/element-kinds, TurboFan/Maglev/Turboshaft speculation bugs; CVE-2024-4947/5274, CVE-2025-2135/5419/10585 patterns. Build addrof/fakeobj and an in-cage arbitrary R/W via a fake TypedArray. Backed by v8_typer.js, d8_debug.sh.
• references/v8-sandbox-escape.md — The V8 heap sandbox (pointer compression, external-pointer & trusted-pointer tables); escaping via raw pointers in Wasm objects (WasmIndirectFunctionTable / Liftoff), Trusted Pointer Table abuse, and pivot to RWX Wasm code. Backed by sandbox_escape.js.
• references/renderer-to-browser-escape.md — Escaping the OS sandbox: Mojo IPC handle-confusion logic bugs (CVE-2025-2783 ForumTroll, CVE-2025-4609 ipcz), GPU-process memory bugs (Dawn/WebGPU, ANGLE CVE-2025-6558), fuzzing Mojo interfaces. Backed by mojo_fuzz_harness.py.
• references/electron-webview-rce.md — Electron/CEF/WebView2 model; nodeIntegration/contextIsolation/sandbox matrix, preload-bridge & IPC abuse, deprecated webviewTag, ASAR integrity bypass (CVE-2025-55305) and V8 snapshot/fuse tampering, XSS->RCE. Backed by electron_audit.py.
• references/clientside-rce-chains.md — Stitching primitives into a reliable 1-click chain; staged delivery, UA/feature gating, reliability hardening, cross-engine (JSC/WebKit CVE-2025-43529) primitive porting, patch-diffing for n-days. Backed by chain_server.py.