CVE-2026-49265 (GCVE-0-2026-49265)

Vulnerability from cvelistv5 – Published: 2026-10-13 15:47 – Updated: 2026-10-13 16:19
VLAI
Title
OAuthLib: Timing Attack Vulnerability in PKCE code_verifier Comparison
Summary
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.
Severity
6.8 (Medium)
CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:U/C:H/I:H/A:N
SSVC
Exploitation: none Automatable: no Technical Impact: total
CISA Coordinator · CISA-ADP (v2.0.3)
Decision recorded 2026-10-13 16:19 UTC
CWE
  • CWE-208 - Observable Timing Discrepancy
Assigner
GitHub_M CNA under the mitre root
CNA scorecard C 72/100 over 7637 records in the last 180 days details
References
Impacted products
Vendor Product Version CPE status
oauthlib oauthlib Affected: >= 3.0.0, < 4.0.0
guessed Create a notification for this product.
Show details on NVD website
To clipboard 

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