---
title: "CVE-2026-26247: Gitea OAuth2 PKCE S256 verifier bypass"
url: https://erroneo.us/security/cve/CVE-2026-26247/
description: "CVE-2026-26247 (code.gitea.io/gitea (Go)): Gitea versions before 1.25.5 do not persist the OAuth2 PKCE S256 challenge method correctly during authorization…"
type: vulnerability-record
section: "Security Digest"
date_published: 2026-07-03
date_modified: 2026-09-01
publisher: erroneo.us
author: erroneo.us Security Desk
cve: "CVE-2026-26247"
kev: false
cvss: 9.1
epss: 0.00495
license: All rights reserved. Quote with attribution and a link.
---

# CVE-2026-26247: Gitea OAuth2 PKCE S256 verifier bypass

**Signal:** Critical and remotely reachable. No known exploitation yet, but it is network-reachable without credentials. (Computed from CISA KEV, EPSS and CVSS; not an editorial verdict.)

## Should you act?

- No confirmed exploitation. It is not in CISA’s KEV catalog and CISA’s SSVC assessment records no known exploitation. That can change quickly after a public write-up; re-check if you are affected.
- EPSS 0.5% , percentile 42: FIRST’s model estimates a 0.5% chance of exploitation activity in the next 30 days, higher than 42% of all scored CVEs (low). EPSS is a probability, not a verdict.
- Remotely reachable with no login and no user interaction. If the vulnerable service is exposed to the internet, prioritize it.
- Only applies if your dependency tree includes code.gitea.io/gitea (Go) < 1.25.5, fixed in 1.25.5 . Check your lockfile, including transitive dependencies.

## What it is

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 packages

- Go `code.gitea.io/gitea` < 1.25.5 → fixed: 1.25.5

## Affected products (CVE record)

- Gitea Gitea Open Source Git Server: < 1.25.5

## Severity

- CISA-ADP CVSS 3.1: 9.1 `CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N`
- GitHub CVSS 3.1: 9.1 `CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N`

## Exploitation

- CISA KEV: not listed (no confirmed in-the-wild exploitation known to CISA).
- CISA SSVC assessment: exploitation none , automatable yes , technical impact total .
- FIRST EPSS (model of 2026-10-21): 0.50% probability of exploitation activity in the next 30 days; percentile 42.

## Sources

- [GitHub Pull Request #36462](https://github.com/go-gitea/gitea/pull/36462)
- [GitHub Pull Request #36477](https://github.com/go-gitea/gitea/pull/36477)
- [Gitea v1.25.5 Release](https://github.com/go-gitea/gitea/releases/tag/v1.25.5)
- [Gitea v1.25.5 Release Blog Post](https://blog.gitea.com/release-of-1.25.5/)
- [GitHub Advisory GHSA-m5ch-ppfx-xv3v](https://github.com/advisories/GHSA-m5ch-ppfx-xv3v)
- [CVE.org record CVE-2026-26247](https://www.cve.org/CVERecord?id=CVE-2026-26247)
- [NVD entry CVE-2026-26247](https://nvd.nist.gov/vuln/detail/CVE-2026-26247)
- [github.com](https://github.com/go-gitea/gitea/commit/750649c1ef092c95f95b206b9d5fa17471a0b1f5)
- [github.com](https://github.com/go-gitea/gitea/commit/bf8d11bb212ba2a76596d8a90e74e7d664571324)

---
Source page: https://erroneo.us/security/cve/CVE-2026-26247/ · Security Digest: https://erroneo.us/security/ · More: https://erroneo.us/llms.txt