CVE-2026-26247: Gitea OAuth2 PKCE S256 challenges are not enforced during token exchange

Severity: critical (CVSS 9.1 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.5% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2026-07-03 · updated 2026-10-25
Weakness: CWE-284

Description

Gitea versions before 1.25.5 do not persist the OAuth2 PKCE S256 challenge method correctly during authorization, allowing token exchange without the expected verifier check.

Affected products

Gitea Open Source Git Server: before 1.25.5 — fixed in 1.25.5

How to fix

Upgrade to a fixed version: Gitea Open Source Git Server 1.25.5. Check the vendor advisory for mitigations.

References

https://blog.gitea.com/release-of-1.25.5/
https://github.com/go-gitea/gitea/pull/36462
https://github.com/go-gitea/gitea/pull/36477
https://github.com/go-gitea/gitea/releases/tag/v1.25.5

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