{"affected":[{"package":{"ecosystem":"Hex","name":"guardian","purl":"pkg:hex/guardian"},"ranges":[{"events":[{"introduced":"1.0.0"},{"fixed":"2.4.1"}],"type":"SEMVER"}],"versions":["1.0.0","1.0.1","1.1.0","1.1.1","1.2.0","1.2.1","2.0.0","2.1.1","2.1.2","2.2.0","2.2.1","2.2.2","2.2.3","2.2.4","2.3.0","2.3.1","2.3.2","2.4.0"]},{"ranges":[{"events":[{"introduced":"d65227145f72b290106c06cecbe42728fbf05fe2"},{"fixed":"2bd7a8c29770d423d855c0a4965caa6c3e486901"}],"repo":"https://github.com/ueberauth/guardian","type":"GIT"}]}],"aliases":["GHSA-7975-hp3r-5qhv","CVE-2026-55735"],"credits":[{"name":"Peter Ullrich","type":"FINDER"},{"name":"Yordis Prieto","type":"REMEDIATION_DEVELOPER"},{"name":"Jonatan Männchen / EEF","type":"ANALYST"}],"database_specific":{"capec_ids":["CAPEC-475"],"cpe_ids":["cpe:2.3:a:ueberauth:guardian:*:*:*:*:*:*:*:*"],"cwe_ids":["CWE-347"]},"details":"## Summary\n\nImproper Verification of Cryptographic Signature in ueberauth guardian allows an unauthenticated attacker to revoke a victim's session with a forged token.\n\nGuardian.revoke/3 in lib/guardian.ex decodes the supplied token with peek/1, which performs no signature verification (it only base64-decodes the JWT header and payload). The resulting unverified claims are forwarded directly to the configured token module's revoke callback and the implementation's on\\_revoke callback, a state-mutating sink. The sibling operations refresh/2 and exchange/4 both call decode\\_and\\_verify first, so the signature is checked before anything acts on the claims; revoke/3 is the only state-mutating path that acts on claims without verifying the signature.\n\nAn attacker who knows or guesses a victim's identifying claim values (jti, sub) can forge a JWT carrying those claims, sign it with an arbitrary key, and submit it to any endpoint that funnels a caller-supplied token into Guardian.revoke/3 (the standard logout / session-revocation pattern). When the token module mutates state keyed by the claims (whitelist deletion or blacklist insertion, for example a GuardianDb-style store), the victim's legitimate session is evicted. This is an unauthenticated session-revocation denial of service; the attacker never needs the signing secret.\n\nThis issue affects guardian: from 1.0.0 before 2.4.1.\n\n## Workaround\n\nVerify the token before revoking it: call decode\\_and\\_verify (or a verify-without-expiry variant, so already-expired tokens remain revocable) on the caller-supplied token and pass only tokens whose signature validates into Guardian.revoke/3. Reject tokens with an invalid signature at the application boundary.\n\n## Configuration\n\nThe application must route a caller-supplied token into Guardian.revoke/3 (for example a logout or session-revocation endpoint) and use a token module whose revoke / on\\_revoke callback mutates state keyed by the token claims (a whitelist that deletes by jti or a blacklist that inserts by jti, such as a GuardianDb-style store). With the default no-op on\\_revoke callback, no session state is changed and the issue is not exploitable.","id":"EEF-CVE-2026-55735","modified":"2026-08-01T18:46:05.234Z","published":"2026-08-01T18:46:05.234Z","references":[{"type":"ADVISORY","url":"https://github.com/ueberauth/guardian/security/advisories/GHSA-7975-hp3r-5qhv"},{"type":"WEB","url":"https://cna.erlef.org/cves/CVE-2026-55735.html"},{"type":"FIX","url":"https://github.com/ueberauth/guardian/commit/2bd7a8c29770d423d855c0a4965caa6c3e486901"},{"type":"PACKAGE","url":"https://hex.pm/packages/guardian"}],"related":[],"schema_version":"1.7.3","severity":[{"score":"CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N","type":"CVSS_V4"}],"summary":"Guardian.revoke/3 acts on unverified token claims, allowing forged-token session revocation","upstream":[]}