{"id":"CVE-2026-55735","aliases":["EEF-CVE-2026-55735","GHSA-7975-hp3r-5qhv"],"url":"https://o3.security/vulnerability/CVE-2026-55735","summary":"Guardian.revoke/3 acts on unverified token claims, allowing forged-token session revocation","details":"Improper 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.","published":"2026-08-01T18:46:05.234Z","modified":"2026-08-12T03:51:14.463812617Z","cvss":null,"epss":{"score":0.00282,"percentile":0.20656,"asOf":"2026-08-17"},"cisaKev":null,"exploitsKnown":0,"affectedPackages":[],"fix":{"url":"https://github.com/ueberauth/guardian/commit/2bd7a8c29770d423d855c0a4965caa6c3e486901","label":"ueberauth/guardian@2bd7a8c"},"references":[{"type":"WEB","url":"https://cna.erlef.org/cves/CVE-2026-55735.html"},{"type":"WEB","url":"https://github.com"},{"type":"WEB","url":"https://osv.dev/vulnerability/EEF-CVE-2026-55735"},{"type":"WEB","url":"https://repo.hex.pm"},{"type":"ADVISORY","url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/55xxx/CVE-2026-55735.json"},{"type":"ADVISORY","url":"https://github.com/ueberauth/guardian/security/advisories/GHSA-7975-hp3r-5qhv"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-55735"},{"type":"FIX","url":"https://github.com/ueberauth/guardian/commit/2bd7a8c29770d423d855c0a4965caa6c3e486901"},{"type":"PACKAGE","url":"https://github.com/ueberauth/guardian"}],"provenance":{"sources":["OSV.dev","FIRST.org (EPSS)"],"lastVerified":"2026-08-12T03:51:14.463812617Z"}}