{"id":"CVE-2026-49265","published":"2026-10-13T16:17:20.713","lastModified":"2026-10-16T20:04:29.760","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.","cvssScore":6.8,"cvssSeverity":"MEDIUM","cvssVector":"CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:U/C:H/I:H/A:N","cwes":["CWE-208"],"vendors":[],"products":[],"references":[{"url":"https://github.com/oauthlib/oauthlib/commit/74664d3fe037a354e180e305135c6bab1747a6b0","tags":[]},{"url":"https://github.com/oauthlib/oauthlib/pull/963","tags":[]},{"url":"https://github.com/oauthlib/oauthlib/releases/tag/v4.0.0","tags":[]},{"url":"https://github.com/oauthlib/oauthlib/security/advisories/GHSA-xpv3-w29h-x7cv","tags":[]},{"url":"https://github.com/pypa/advisory-database/tree/main/vulns/oauthlib/PYSEC-2026-4114.yaml","tags":[]}],"exploitRefs":[{"url":"https://github.com/oauthlib/oauthlib/commit/74664d3fe037a354e180e305135c6bab1747a6b0","tags":[]},{"url":"https://github.com/oauthlib/oauthlib/pull/963","tags":[]},{"url":"https://github.com/oauthlib/oauthlib/releases/tag/v4.0.0","tags":[]},{"url":"https://github.com/oauthlib/oauthlib/security/advisories/GHSA-xpv3-w29h-x7cv","tags":[]},{"url":"https://github.com/pypa/advisory-database/tree/main/vulns/oauthlib/PYSEC-2026-4114.yaml","tags":[]}],"hasPoc":true,"ai":null}