Skip to content
BetterWrightDocs
Browse docs

Chromium Fork Fingerprint Patch Set

Build-side patches for the pinned BetterWright Chromium 150 fork. The JS layer (src/fork-identity.ts) already masks UA, UA-CH, navigator.platform, and screen geometry via launch flags + CDP emulation. The surfaces below are only reachable from Chromium source — patch them so the binary is coherent even where CDP cannot reach (service workers, WebGL, canvas, fonts).

All values come from a real capture machine: MacBook Pro 14" (Mac16,8), Apple M4 Pro, 12 cores / 24 GB, macOS 26.6, display 1800x1169 @2x, running genuine Google Chrome 150.0.7871.129. Gate every patch on --fingerprint-platform=macos (the flag the launcher passes) and key per-profile variation to --fingerprint=<seed>.

1. Platform identity at source (replaces the CDP stopgap)

Once these land, the CDP Emulation.setUserAgentOverride layer can be retired for the fork — source is authoritative, and service workers inherit it automatically.

components/embedder_support/user_agent_utils.cc

  • GetUserAgent(): when masked, force Mozilla/5.0 (Macintosh; Intel Mac OS X 10_15_7) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/<major>.0.0.0 Safari/537.36 — and never emit the Headless marker in --headless mode (the stock headless UA is an instant tell).
  • GetUserAgentMetadata(): platform = "macOS", platform_version = "26.6.0", architecture = "arm", model = "", bitness = "64", mobile = false.
  • Brand list (GenerateBrandVersionList / GetBrandVersionList): emit the real consumer-Chrome triple — Not;A=Brand v8(.0.0.0), Chromium v<major>, Google Chrome v<full>.

third_party/blink/renderer/core/frame/navigator_id.cc

  • NavigatorID::platform(): return "MacIntel" when masked. (Real Apple Silicon Chrome still reports MacIntel — do not invent MacARM.)

2. WebGL

third_party/blink/renderer/modules/webgl/webgl_rendering_context_base.cc

In WebGLRenderingContextBase::getParameter, intercept UNMASKED_VENDOR_WEBGL / UNMASKED_RENDERER_WEBGL (extension WEBGL_debug_renderer_info) when masked:

case GLenum(Extensions3D::kUnmaskedVendor):
  return String("Google Inc. (Apple)");
case GLenum(Extensions3D::kUnmaskedRenderer):
  return String("ANGLE (Apple, ANGLE Metal Renderer: Apple M4 Pro, "
                "Unspecified Version)");

Leave VENDOR/RENDERER returning WebKit / WebKit WebGL — that is what real Chrome returns for the non-debug parameters. Also patch the WebGL2 path (webgl2_rendering_context_base.cc shares the base implementation; verify the single interception covers both) and GPU process info strings if any diagnostic surface exposes the real GL renderer (e.g. chrome://gpu is not web-visible, but WEBGL_debug_renderer_info via WebGL1 contexts is).

3. Canvas noise (unique but stable per profile)

Goal: a canvas hash that is unique to this profile+seed and stable across restarts — per-session randomization is itself a detection signal.

A shared renderer helper (third_party/blink/renderer/platform/graphics/fingerprint_noise.{h,cc}) applies FNV-1a over the --fingerprint seed + splitmix64 per pixel; ±1 on one color channel per pixel, alpha untouched. Hook it at every readback surface:

  • image_data_buffer.cc — ImageDataBuffer::FarbleIfEnabled() copies the readback and re-points pixmap_ (covers toDataURL, toBlob, OffscreenCanvas.convertToBlob, audits). Never writes into peekPixels memory (that is the live canvas backing store).
  • base_rendering_context_2d.cc — getImageData after a successful readPixels.
  • webgl_rendering_context_base.cc — WebGL readPixels (RGBA/ UNSIGNED_BYTE).

Acceptance, verified on a Linux x64 host: identical canvasHash/ getImageDataHash/webglReadPixelsHash across two cold starts with one seed; all three change with a different seed.

4. Audio

offline_audio_context.cc — FireCompletionEvent() applies ApplyFingerprintAudioNoise (±5e-7, seed+channel keyed) to every channel of the rendered buffer. Must be stable per profile and distinct per seed.

5. Hardware surfaces

  • navigator_base.cc: hardwareConcurrency → 12 when masked. (The CDP Emulation.setHardwareConcurrencyOverride stopgap covers pages only.)
  • navigator_device_memory.cc: deviceMemory → 16 — the bucketed value real Chrome reports on the 24 GB capture machine.

6. Screen geometry

ui/ozone/platform/headless/headless_screen.cc: with the Mac mask, bounds 3600×2338 physical + TLBR(78,0,162,0) insets under --force-device-scale-factor=2 → CSS 1800×1169, availHeight 1049, dpr 2. Do not regress the physical-pixel math.

7. Fonts (the hardest Linux→Mac tell)

  • scripts/assemble-mac-fonts.sh (run on macOS) copies 36 mac-metric fonts (Helvetica/Helvetica Neue, Arial set, Times NR set, Courier New, Georgia, Verdana, Trebuchet, Menlo, Monaco, SFNS, Palatino, Futura, Avenir Next, Apple Color Emoji…) into artifacts/linux-x64/fonts/ttf.
  • The worker generates an absolute-path fonts.conf in the profile runtime dir and launches the fork with FONTCONFIG_FILE pointing at it (src/fork-identity.ts: prepareForkFontsConfig, gated on the Mac mask).
  • Acceptance, verified on a Linux x64 host: fc-list enumerates 470 faces; measureText widths differ per family (Helvetica Neue 291 / Menlo 247 / Georgia 307 / Palatino 307 / Avenir Next 304) instead of collapsing to one fallback.

8. Build flags

out/LinuxStatic builds with proprietary_codecs=true, ffmpeg_branding="Chrome", is_component_build=false, target_cpu="x64".

Acceptance

The headless Linux x64 fork behind residential egress must return a real Google SERP (sorryUrl:false, unusualTraffic:false, resultish:true) for the same query a genuine Mac passes, once timezone and locale match the egress IP (e.g. timezone: "Asia/Singapore", locale: "en-US" for a Singapore exit — or geoip: true with an upstream proxy). A UTC timezone paired with a residential exit IP in another region is a coherence break on its own, even with every other surface patched.

Validation after build

BETTERWRIGHT_CHROMIUM_PATH=/path/to/linux-x64/chrome \
  npm run build:harness
  node scripts/stealth-report.js --live

Probe checklist: navigator.platform → MacIntel; UA/UA-CH macOS in both page and service-worker requests; WebGL debug strings as above; canvas hash stable across two launches with the same profile, different across two profiles; screen.availHeight 1049; fc-list | wc -l inside the browser matches the bundled set; no Headless in UA under --headless.