CVE-2026-49265: Oauthlib: Timing Attack Vulnerability in PKCE code_verifier Comparison (CWE-208)

September 29, 2026

A timing side-channel vulnerability exists in the PKCE (RFC 7636) implementation of the Authorization Code Grant flow. The code_challenge_method_plain function uses Python’s standard == operator for string comparison instead of a constant-time comparison function, potentially allowing timing-based attacks.

References

github.com/advisories/GHSA-xpv3-w29h-x7cv
github.com/oauthlib/oauthlib/commit/40b0ab56da3682c2484a4b78bbff309f8025d950
github.com/oauthlib/oauthlib/pull/963
github.com/oauthlib/oauthlib/security/advisories/GHSA-xpv3-w29h-x7cv
nvd.nist.gov/vuln/detail/CVE-2026-49265

Code Behaviors & Features

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