{"id":"CVE-2026-49265","summary":"OAuthLib: Timing Attack Vulnerability in PKCE code_verifier Comparison","details":"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.","aliases":["GHSA-xpv3-w29h-x7cv","PYSEC-2026-4114"],"modified":"2026-10-28T02:30:27.851305240Z","published":"2026-10-13T15:47:11.854Z","related":["SUSE-SU-2026:24139-1","SUSE-SU-2026:24189-1","SUSE-SU-2026:24246-1","SUSE-SU-2026:4810-1","openSUSE-SU-2026:22103-1"],"database_specific":{"cwe_ids":["CWE-208"],"osv_generated_from":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/49xxx/CVE-2026-49265.json","cna_assigner":"GitHub_M"},"references":[{"type":"WEB","url":"https://github.com/oauthlib/oauthlib/releases/tag/v4.0.0"},{"type":"ADVISORY","url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/49xxx/CVE-2026-49265.json"},{"type":"ADVISORY","url":"https://github.com/oauthlib/oauthlib/security/advisories/GHSA-xpv3-w29h-x7cv"},{"type":"ADVISORY","url":"https://github.com/pypa/advisory-database/tree/main/vulns/oauthlib/PYSEC-2026-4114.yaml"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-49265"},{"type":"FIX","url":"https://github.com/oauthlib/oauthlib/commit/74664d3fe037a354e180e305135c6bab1747a6b0"},{"type":"FIX","url":"https://github.com/oauthlib/oauthlib/pull/963"}],"affected":[{"ranges":[{"type":"GIT","repo":"https://github.com/oauthlib/oauthlib","events":[{"introduced":"9dfa40c3bdab3aa788e711283afdf36c2fbdd1de"},{"fixed":"145a9a4690cb4d9de30d15fcc2984e34c49df741"},{"fixed":"74664d3fe037a354e180e305135c6bab1747a6b0"}],"database_specific":{"extracted_events":[{"source":"AFFECTED_FIELD","strategy":"StringRangeExpression","range":[{"introduced":"3.0.0"},{"fixed":"4.0.0"}]},{"source":"REFERENCES_COMMIT","range":[{"fixed":"74664d3fe037a354e180e305135c6bab1747a6b0"}]},{"source":"REFERENCES_TAG","original_tag":"v4.0.0","range":[{"fixed":"145a9a4690cb4d9de30d15fcc2984e34c49df741"}]}]}}],"versions":["v3.3.0","v3.1.0","v3.0.1","v3.0.0"],"database_specific":{"source":"https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-49265.json"}}],"schema_version":"1.9.2","severity":[{"type":"CVSS_V3","score":"CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:U/C:H/I:H/A:N"}]}