What is CVE-2021-39889?

CVE-2021-39889 is a medium-severity vulnerability in GitLab, classified under Authorization Bypass Through User-Controlled Key. CVSS score: 4.3/10. Published 2021-10-05.

How severe is CVE-2021-39889?

Medium severity. CVSS v3 base score is 4.3 out of 10.

Auth bypass in GitLab

CVE-2021-39889

In all versions of GitLab EE since version 14.1, due to an insecure direct object reference vulnerability, an endpoint may reveal the protected branch name to a malicious user who makes a crafted API call with the ID of the protected branch.

Vulnerability class: IDOR (Insecure Direct Object Reference)

Published 2021-10-05 · last modified 2026-06-17.

CVSS v3 metric

CVSS v3 base score 4.3 (Medium). Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:N/A:N.

EPSS exploit prediction

EPSS: 0.008 (56.0th percentile), scored 2026-09-29.

Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 56th percentile — 56.0% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.

EPSS over last 30 days · oldest: 0.008 · newest: 0.008 · change: 0.000

Affected products

GitLab — versions >=14.1, <14.1.7, >=14.2, <14.2.5, >=14.3, <14.3.1

Weakness classification (CWE)

CWE-639 — Authorization Bypass Through User-Controlled Key

References

gitlab.com/gitlab-org/gitlab/-/issues/338062 (Broken Link)
hackerone.com/reports/1294017 (Permissions Required, Third Party Advisory)
gitlab.com/gitlab-org/cves/-/blob/master/2021/CVE-2021-39889.json (Vendor Advisory)

Frequently asked questions

What is CVE-2021-39889?: CVE-2021-39889 is a medium-severity vulnerability in GitLab, classified under Authorization Bypass Through User-Controlled Key. CVSS score: 4.3/10. Published 2021-10-05.
How severe is CVE-2021-39889?: Medium severity. CVSS v3 base score is 4.3 out of 10.