CVE-2023-3909: Inefficient Regular Expression Complexity in GitLab

Severity: medium (CVSS 6.5 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.6% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2023-11-06 · updated 2026-06-17
Weakness: CWE-1333

Description

An issue has been discovered in GitLab CE/EE affecting all versions starting from 12.3 before 16.3.6, all versions starting from 16.4 before 16.4.2, all versions starting from 16.5 before 16.5.1. A Regular Expression Denial of Service was possible by adding a large string in timeout input in gitlab-ci.yml file.

Affected products

GitLab: from 12.3.0 before 16.3.6; from 16.4.0 before 16.4.2; 16.5.0 — fixed in 16.3.6, 16.4.2

How to fix

Upgrade to a fixed version: GitLab 16.3.6, 16.4.2. Check the vendor advisory for mitigations.

References

https://gitlab.com/gitlab-org/gitlab/-/issues/418763
https://hackerone.com/reports/2050269
https://gitlab.com/gitlab-org/gitlab/-/issues/418763
https://hackerone.com/reports/2050269

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