{"id":"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.","aliases":["EEF-CVE-2026-55735","GHSA-7975-hp3r-5qhv"],"modified":"2026-08-03T03:30:22.762195668Z","published":"2026-08-01T18:46:05.234Z","database_specific":{"osv_generated_from":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/55xxx/CVE-2026-55735.json","unresolved_ranges":[{"source":"AFFECTED_FIELD","extracted_events":[{"introduced":"d65227145f72b290106c06cecbe42728fbf05fe2"},{"fixed":"2bd7a8c29770d423d855c0a4965caa6c3e486901"}]}],"cna_assigner":"EEF","cwe_ids":["CWE-347"]},"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"}],"affected":[{"ranges":[{"type":"GIT","repo":"https://github.com/ueberauth/guardian","events":[{"introduced":"b15e86c868f76631818a13e76759dfae7693b1ec"},{"fixed":"e6017b492b8ef55e24fd08dea45ce11780d7b4f7"},{"fixed":"2bd7a8c29770d423d855c0a4965caa6c3e486901"}],"database_specific":{"extracted_events":[{"introduced":"1.0.0"},{"fixed":"2.4.1"}],"source":["DESCRIPTION","REFERENCES"]}}],"versions":["v2.4.0","v2.3.2","v2.3.1","v2.3.0","v2.2.4","v2.2.3","v2.2.2","v2.2.1","v2.1.2","v2.1.1","2.1.0","v2.0.0","v1.2.1","v1.2.0","v1.1.1","v1.1.0","v1.0.1","v1.0.0"],"database_specific":{"source":"https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-55735.json"}}],"schema_version":"1.7.5","severity":[{"type":"CVSS_V4","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"}]}