Improper Input Validation in GitLab Affects User Browser Security
CVE-2026-3254

3.5LOW

Key Information:

Vendor

Gitlab
Status
Gitlab
Vendor
CVE Published:
22 April 2026

What is CVE-2026-3254?

GitLab has addressed a flaw in the GitLab CE/EE product where improper input validation in the Mermaid sandbox could allow an authenticated user to inject unauthorized content into another user's web browser. This vulnerability affects all versions of GitLab from 18.11 prior to 18.11.1, presenting potential risks in user session integrity and overall security. Users are advised to update their installations promptly to mitigate possible exploitation.

Affected Version(s)

GitLab 18.11 < 18.11.1

References

https://hackerone.com/reports/3572752
technical-descriptionexploitpermissions-required
https://gitlab.com/gitlab-org/gitlab/-/work_items/591587

CVSS V3.1

Score:
3.5
Severity:
LOW
Confidentiality:
None
Integrity:
Low
Availability:
None
Attack Vector:
Network
Attack Complexity:
Low
Privileges Required:
Low
User Interaction:
Required
Scope:
Unchanged

Timeline

  • Vulnerability published

  • Vulnerability Reserved

Credit

Thanks [joaxcar](https://hackerone.com/joaxcar) for reporting this vulnerability through our HackerOne bug bounty program
.