The 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.
" } ], "value": "The 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." } ], "cpeApplicability": [ { "nodes": [ { "cpeMatch": [ { "criteria": "cpe:2.3:a:ueberauth:guardian:*:*:*:*:*:*:*:*", "versionEndExcluding": "2.4.1", "versionStartIncluding": "1.0.0", "vulnerable": true } ], "negate": false, "operator": "OR" } ] } ], "credits": [ { "lang": "en", "type": "finder", "value": "Peter Ullrich" }, { "lang": "en", "type": "remediation developer", "value": "Yordis Prieto" }, { "lang": "en", "type": "analyst", "value": "Jonatan Männchen / EEF" } ], "descriptions": [ { "lang": "en", "supportingMedia": [ { "base64": false, "type": "text/html", "value": "Improper Verification of Cryptographic Signature in ueberauth guardian allows an unauthenticated attacker to revoke a victim's session with a forged token.
Guardian.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.
An 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.
This issue affects guardian: from 1.0.0 before 2.4.1.
" } ], "value": "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." } ], "impacts": [ { "capecId": "CAPEC-475", "descriptions": [ { "lang": "en", "value": "CAPEC-475 Signature Spoofing by Improper Validation" } ] } ], "metrics": [ { "cvssV4_0": { "attackComplexity": "LOW", "attackRequirements": "PRESENT", "attackVector": "NETWORK", "baseScore": 8.2, "baseSeverity": "HIGH", "privilegesRequired": "NONE", "subAvailabilityImpact": "NONE", "subConfidentialityImpact": "NONE", "subIntegrityImpact": "NONE", "userInteraction": "NONE", "vectorString": "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", "version": "4.0", "vulnAvailabilityImpact": "HIGH", "vulnConfidentialityImpact": "NONE", "vulnIntegrityImpact": "NONE" }, "format": "CVSS", "scenarios": [ { "lang": "en", "value": "GENERAL" } ] } ], "problemTypes": [ { "descriptions": [ { "cweId": "CWE-347", "description": "CWE-347 Improper Verification of Cryptographic Signature", "lang": "en", "type": "CWE" } ] } ], "providerMetadata": { "orgId": "6b3ad84c-e1a6-4bf7-a703-f496b71e49db", "shortName": "EEF", "dateUpdated": "2026-08-01T18:46:05.234Z" }, "references": [ { "tags": [ "vendor-advisory", "related" ], "url": "https://github.com/ueberauth/guardian/security/advisories/GHSA-7975-hp3r-5qhv" }, { "tags": [ "related" ], "url": "https://cna.erlef.org/cves/CVE-2026-55735.html" }, { "tags": [ "related" ], "url": "https://osv.dev/vulnerability/EEF-CVE-2026-55735" }, { "tags": [ "patch" ], "url": "https://github.com/ueberauth/guardian/commit/2bd7a8c29770d423d855c0a4965caa6c3e486901" } ], "source": { "discovery": "EXTERNAL" }, "title": "Guardian.revoke/3 acts on unverified token claims, allowing forged-token session revocation", "workarounds": [ { "lang": "en", "supportingMedia": [ { "base64": false, "type": "text/html", "value": "Verify 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.
" } ], "value": "Verify 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." } ], "x_generator": { "engine": "cvelib 1.8.0" } }, "adp": [ { "references": [ { "url": "https://github.com/ueberauth/guardian/security/advisories/GHSA-7975-hp3r-5qhv", "tags": [ "exploit" ] } ], "metrics": [ { "other": { "type": "ssvc", "content": { "timestamp": "2026-08-03T19:29:43.841542Z", "id": "CVE-2026-55735", "options": [ { "Exploitation": "poc" }, { "Automatable": "no" }, { "Technical Impact": "partial" } ], "role": "CISA Coordinator", "version": "2.0.3" } } } ], "title": "CISA ADP Vulnrichment", "providerMetadata": { "orgId": "134c704f-9b21-4f2e-91b3-4a467353bcc0", "shortName": "CISA-ADP", "dateUpdated": "2026-08-03T19:30:07.608Z" } } ] } }