{"id":"CVE-2026-49265","state":"PUBLISHED","title":"OAuthLib: Timing Attack Vulnerability in PKCE code_verifier Comparison","description":"OAuthLib is an implementation of the OAuth request-signing logic for Python 3.6+. From 3.0.0 until 4.0.0, OAuthLib's PKCE checks in oauthlib/oauth2/rfc6749/grant_types/authorization_code.py compare attacker-supplied code_verifier values with stored challenges using ordinary string equality in code_challenge_method_plain and code_challenge_method_s256. Because the comparison can return after a length difference or the first mismatching character, repeated token endpoint measurements can reveal common-prefix timing information that could potentially allow recovery of the code_verifier, unauthorized access-token acquisition, and account takeover. Practical exploitation requires an intercepted, single-use authorization code and enough measurements to overcome real-world network noise; the local timing benchmark does not establish practical remote account takeover, so the weakness remains a defense-in-depth concern. This issue is fixed in version 4.0.0.","publishedAt":"2026-10-13T15:47:11.854Z","updatedAt":"2026-10-13T16:19:39.092Z","severity":{"score":6.8,"label":"Medium","version":"3.1","vector":"CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:U/C:H/I:H/A:N","source":"GitHub_M"},"assigner":"GitHub_M","products":["oauthlib oauthlib"],"affected":[{"vendor":"oauthlib","product":"oauthlib","versions":[{"version":">= 3.0.0, < 4.0.0","status":"affected"}]}],"references":["https://github.com/oauthlib/oauthlib/security/advisories/GHSA-xpv3-w29h-x7cv","https://github.com/oauthlib/oauthlib/pull/963","https://github.com/oauthlib/oauthlib/commit/74664d3fe037a354e180e305135c6bab1747a6b0","https://github.com/oauthlib/oauthlib/releases/tag/v4.0.0","https://github.com/pypa/advisory-database/tree/main/vulns/oauthlib/PYSEC-2026-4114.yaml"],"weaknesses":["CWE-208"],"ingestedAt":"2026-10-29T20:12:07.131Z","source":{"repository":"CVEProject/cvelistV5","path":"cves/2026/49xxx/CVE-2026-49265.json","commit":"556c9d3a8cd17e218bb8e452ba7cd619a384ff47"},"raw":{"dataType":"CVE_RECORD","dataVersion":"5.2","cveMetadata":{"cveId":"CVE-2026-49265","state":"PUBLISHED","datePublished":"2026-10-13T15:47:11.854Z","dateUpdated":"2026-10-13T16:19:39.092Z","assignerShortName":"GitHub_M","assignerOrgId":"a0819718-46f1-4df5-94e2-005712e83aaa","dateReserved":"2026-05-28T14:33:01.180Z"},"containers":{"cna":{"title":"OAuthLib: Timing Attack Vulnerability in PKCE code_verifier Comparison","descriptions":[{"lang":"en","value":"OAuthLib is an implementation of the OAuth request-signing logic for Python 3.6+. From 3.0.0 until 4.0.0, OAuthLib's PKCE checks in oauthlib/oauth2/rfc6749/grant_types/authorization_code.py compare attacker-supplied code_verifier values with stored challenges using ordinary string equality in code_challenge_method_plain and code_challenge_method_s256. Because the comparison can return after a length difference or the first mismatching character, repeated token endpoint measurements can reveal common-prefix timing information that could potentially allow recovery of the code_verifier, unauthorized access-token acquisition, and account takeover. Practical exploitation requires an intercepted, single-use authorization code and enough measurements to overcome real-world network noise; the local timing benchmark does not establish practical remote account takeover, so the weakness remains a defense-in-depth concern. This issue is fixed in version 4.0.0."}],"affected":[{"vendor":"oauthlib","product":"oauthlib","versions":[{"version":">= 3.0.0, < 4.0.0","status":"affected"}]}],"references":[{"url":"https://github.com/oauthlib/oauthlib/security/advisories/GHSA-xpv3-w29h-x7cv","name":"https://github.com/oauthlib/oauthlib/security/advisories/GHSA-xpv3-w29h-x7cv","tags":["x_refsource_CONFIRM"]},{"url":"https://github.com/oauthlib/oauthlib/pull/963","name":"https://github.com/oauthlib/oauthlib/pull/963","tags":["x_refsource_MISC"]},{"url":"https://github.com/oauthlib/oauthlib/commit/74664d3fe037a354e180e305135c6bab1747a6b0","name":"https://github.com/oauthlib/oauthlib/commit/74664d3fe037a354e180e305135c6bab1747a6b0","tags":["x_refsource_MISC"]},{"url":"https://github.com/oauthlib/oauthlib/releases/tag/v4.0.0","name":"https://github.com/oauthlib/oauthlib/releases/tag/v4.0.0","tags":["x_refsource_MISC"]},{"url":"https://github.com/pypa/advisory-database/tree/main/vulns/oauthlib/PYSEC-2026-4114.yaml","name":"https://github.com/pypa/advisory-database/tree/main/vulns/oauthlib/PYSEC-2026-4114.yaml","tags":["x_refsource_MISC"]}],"metrics":[{"cvssV3_1":{"attackComplexity":"HIGH","attackVector":"NETWORK","availabilityImpact":"NONE","baseScore":6.8,"baseSeverity":"MEDIUM","confidentialityImpact":"HIGH","integrityImpact":"HIGH","privilegesRequired":"NONE","scope":"UNCHANGED","userInteraction":"REQUIRED","vectorString":"CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:U/C:H/I:H/A:N","version":"3.1"}}],"problemTypes":[{"descriptions":[{"cweId":"CWE-208","lang":"en","description":"CWE-208: Observable Timing Discrepancy","type":"CWE"}]}],"providerMetadata":{"shortName":"GitHub_M","orgId":"a0819718-46f1-4df5-94e2-005712e83aaa","dateUpdated":"2026-10-13T15:47:11.854Z"},"source":{"advisory":"GHSA-xpv3-w29h-x7cv","discovery":"UNKNOWN"}},"adp":[{"title":"CISA ADP Vulnrichment","metrics":[{"other":{"type":"ssvc","content":{"timestamp":"2026-10-13T16:19:32.600149Z","id":"CVE-2026-49265","options":[{"Exploitation":"none"},{"Automatable":"no"},{"Technical Impact":"total"}],"role":"CISA Coordinator","version":"2.0.3"}}}],"providerMetadata":{"shortName":"CISA-ADP","orgId":"134c704f-9b21-4f2e-91b3-4a467353bcc0","dateUpdated":"2026-10-13T16:19:39.092Z"}}]}}}