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fix(express): prevent auth bypass from foreign req.auth values - #8804
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clerkMiddleware() and requireAuth() skipped Clerk authentication whenever req.auth was truthy, a property name shared with express-jwt, passport, and express-openid-connect. Any app pairing one of those with @clerk/express had Clerk auth silently bypassed, and getAuth() returned the unverified foreign value. Brand the auth handler Clerk installs with a Symbol.for() key and gate the skip-check, getAuth's type guard, and requireAuth on that brand. Clerk now authenticates and overwrites a foreign req.auth (warning once when it does) instead of trusting it. Fixes SDK-76
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🦋 Changeset detectedLatest commit: 09aaa45 The changes in this PR will be included in the next version bump. This PR includes changesets to release 1 package
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📝 WalkthroughWalkthroughThis PR hardens Clerk's Express integration against authentication bypass by introducing a branded marker for Clerk-authenticated requests and updating ChangesExpress Authentication Bypass Hardening
Estimated code review effort🎯 3 (Moderate) | ⏱️ ~25 minutes Poem
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No API Changes DetectedAll packages have stable APIs with no detected changes. Report generated by Break Check Last ran on |
@clerk/astro@clerk/backend@clerk/chrome-extension@clerk/clerk-js@clerk/expo@clerk/expo-passkeys@clerk/express@clerk/fastify@clerk/hono@clerk/localizations@clerk/nextjs@clerk/nuxt@clerk/react@clerk/react-router@clerk/shared@clerk/tanstack-react-start@clerk/testing@clerk/ui@clerk/upgrade@clerk/vuecommit: |
wobsoriano
approved these changes
Jun 10, 2026
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+160
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| if ('auth' in request) { | ||
| logger.warnOnce( | ||
| 'Clerk: another middleware has already set `req.auth` on this request. Clerk authentication will run anyway and overwrite it. To use another auth library alongside Clerk, configure it to store its state on a different request property.', | ||
| ); | ||
| } |
| * globally so it stays stable across multiple copies of this package loaded in | ||
| * the same process. | ||
| */ | ||
| const clerkAuthBrand = Symbol.for('@clerk/express.auth'); |
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clerkMiddleware()opened its handler by bailing out early ifreq.authwas already truthy, to avoid re-authenticating when the middleware runs twice. The problem is thatreq.authis a property name shared with express-jwt, Passport, and express-openid-connect, so in any app that pairs one of those with@clerk/express, Clerk authentication was skipped on every request andgetAuth()returned the other library's unverified value.requireAuth()and therequestHasAuthObjecttype guard had the same blind spot.The fix brands the
req.authhandler Clerk installs with aSymbol.for('@clerk/express.auth')key, and the "did Clerk already run?" checks now gate on that brand rather than on the property's presence:A foreign
req.authno longer satisfies the guard, so Clerk authenticates the request and overwrites the value (warning once when it does). The publicreq.auth(options)surface is unchanged and the legitimate double-clerkMiddlewareno-op still holds, since only Clerk's own handler carries the brand. Worth a close look at the three gated call sites: the skip guard inauthenticateRequest.ts,getAuth, andrequireAuth.ts:52.Fixes SDK-76.