CVE-2026-49265
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.
- CVSS 3.1
- 6.8
CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:U/C:H/I:H/A:N - EPSS
- 0.2% chance of exploitation in the next 30 days; higher than 15% of CVEs (scores of 2026-10-25)
- CWE
- CWE-208
- Published
- Modified
- Record from
- the NVD, synced
Packages (OSV)
| Advisory | Ecosystem | Package | Affected | Fixed in |
|---|---|---|---|---|
| GHSA-xpv3-w29h-x7cv | PyPI | oauthlib | >=3.0.0 <4.0.0 | 4.0.0 |
| PYSEC-2026-4114 | PyPI | oauthlib | >=3.0.0 <4.0.0 | 4.0.0 |
References
- https://github.com/oauthlib/oauthlib/commit/74664d3fe037a354e180e305135c6bab1747a6b0
- https://github.com/oauthlib/oauthlib/pull/963
- https://github.com/oauthlib/oauthlib/releases/tag/v4.0.0
- https://github.com/oauthlib/oauthlib/security/advisories/GHSA-xpv3-w29h-x7cv
- https://github.com/pypa/advisory-database/tree/main/vulns/oauthlib/PYSEC-2026-4114.yaml