Security Digest · Vulnerability record
CVE-2026-26247: Gitea OAuth2 PKCE S256 verifier bypass
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.
CVSS 9.1 Critical EPSS 0.5% · p42
Should you act?
Critical and remotely reachable
No known exploitation yet, but it is network-reachable without credentials. This signal is computed from CISA KEV, EPSS and CVSS data; it is not an editorial verdict.
- 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.
From the GitHub advisory
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.
Weakness type: CWE-284.
Product: code.gitea.io/gitea (Go) · Assigned by: Gitea · Published: 2026-07-03
Affected and fixed versions
| Ecosystem | Package | Vulnerable | First fixed |
|---|---|---|---|
| Go | code.gitea.io/gitea | < 1.25.5 | 1.25.5 |
| Vendor | Product | Affected versions (per CVE record) |
|---|---|---|
| Gitea | Gitea Open Source Git Server | < 1.25.5 |
Severity scores
| Scored by | CVSS | Score | Vector |
|---|---|---|---|
| CISA-ADP | 3.1 | 9.1 Critical | CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N |
| GitHub | 3.1 | 9.1 | CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N |
- Attack vector: network (remotely reachable)
- Attack complexity: low
- Privileges required: none (no login)
- User interaction: none
- Scope: unchanged
CVSS measures how bad a flaw is if exploited, not how likely exploitation is. Read it next to the exploitation data below.
Exploitation and urgency
- 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.
Timeline
- — CVE record published by Gitea
- — GitHub-reviewed advisory GHSA-m5ch-ppfx-xv3v published (critical)
- — CVE record last updated
Sources and references
Original sources first. Version and fix details should always be confirmed against the vendor or project advisory.
Vendor and project advisories, patches
- GitHub Pull Request #36462 github.com
- GitHub Pull Request #36477 github.com
- Gitea v1.25.5 Release github.com
- Gitea v1.25.5 Release Blog Post blog.gitea.com
Vulnerability records
- GitHub Advisory GHSA-m5ch-ppfx-xv3v github.com
- CVE.org record CVE-2026-26247 cve.org
- NVD entry CVE-2026-26247 nvd.nist.gov
Other references from the CVE record and advisory
- github.com github.com
- github.com github.com