fix(auth0-express): reject userinfo (@) in inferred base URL host - #45
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frederikprijck wants to merge 1 commit into
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fix(auth0-express): reject userinfo (@) in inferred base URL host#45frederikprijck wants to merge 1 commit into
frederikprijck wants to merge 1 commit into
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A Host or X-Forwarded-Host header like `legitimate.com@evil.com` is parsed by the URL constructor as userinfo `legitimate.com` with origin `evil.com`. In dynamic (undefined) base-URL mode this value is trusted directly, and previously nothing rejected the userinfo, letting an attacker smuggle an attacker-controlled origin past the origin checks that consume the inferred base URL. Reject any inferred host containing `@`. Hardens the origin checks in `createRouteUrl`/`toSafeRedirect` as defense-in-depth.
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Summary
Hardens dynamic base-URL inference against Host-header userinfo injection, flagged in a security review.
When
appBaseUrlisundefined(dynamic mode),inferBaseUrlFromRequestbuilds the base URL from theHost(or trustedX-Forwarded-Host) header. A header likelegitimate.com@evil.comis parsed by the URL constructor as userinfolegitimate.comwith originevil.com. Since the inferred value feeds the origin checks increateRouteUrl/toSafeRedirect, a smuggled userinfo component could confuse origin determination.This change rejects any inferred host containing
@, returningnull(which surfaces as anInvalidConfigurationErrorinresolveAppBaseUrl).Context / severity
This is defense-in-depth, not a confirmed exploitable open redirect:
Hostheader is already trusted by design, and theredirect_uriis derived from the same inferred base URL — so Auth0's registered-callback-URL validation independently rejects the poisoned URI. The@trick grants no extra capability over simply sendingHost: evil.com.Still, rejecting
@is cheap and correct — the existing spec test already earmarked this as future hardening.Changes
app-base-url.ts: reject inferred hosts containing@.app-base-url.spec.ts: flip the previously-documented "current behaviour" test to assertnull, and add anX-Forwarded-Hostcase.Testing
vitest run— 207 passednpm run lint— clean🤖 Generated with Claude Code