CVE-2025-12653: Authentication Bypass by Spoofing in GitLab

Severity: medium (CVSS 6.5 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.3% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2025-11-26 · updated 2026-10-18
Weakness: CWE-290

Description

GitLab has remediated an issue in GitLab CE/EE affecting all versions from 18.3 before 18.4.5, 18.5 before 18.5.3, and 18.6 before 18.6.1 that under specific conditions could have allowed an unauthenticated user to join arbitrary organizations by changing headers on some requests.

Affected products

GitLab: from 18.3.0 before 18.4.5; from 18.5.0 before 18.5.3; 18.6.0 — fixed in 18.4.5, 18.5.3

How to fix

Upgrade to a fixed version: GitLab 18.4.5, 18.5.3. Check the vendor advisory for mitigations.

References

https://about.gitlab.com/releases/2025/11/26/patch-release-gitlab-18-6-1-released/
https://gitlab.com/gitlab-org/gitlab/-/issues/579372
https://hackerone.com/reports/3370245

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