What is CVE-2021-39906?

CVE-2021-39906 is a high-severity vulnerability in GitLab, classified under Cross-site Scripting. CVSS score: 8.7/10. Published 2021-11-05.

How severe is CVE-2021-39906?

High severity. CVSS v3 base score is 8.7 out of 10.

Is CVE-2021-39906 known to be exploited?

1 public proof-of-concept repositories are indexed. Not currently listed in the CISA KEV catalog.

XSS in GitLab

CVE-2021-39906

Improper validation of ipynb files in GitLab CE/EE version 13.5 and above allows an attacker to execute arbitrary JavaScript code on the victim's behalf.

Vulnerability class: XSS (Cross-Site Scripting)

Published 2021-11-05 · last modified 2026-06-17.

CVSS v3 metric

CVSS v3 base score 8.7 (High). Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:H/I:H/A:N.

EPSS exploit prediction

EPSS: 0.607 (99.1th percentile), scored 2026-10-28.

High probability of exploitation in the next 30 days — patch promptly. 99th percentile — 99.1% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.

EPSS over last 30 days · oldest: 0.607 · newest: 0.607 · change: 0.000

Affected products

GitLab — versions >=13.5, <14.2.6, >=14.3, <14.3.4, >=14.4, <14.4.1

Weakness classification (CWE)

CWE-79 — Cross-site Scripting

Public proof-of-concept exploits

ARPSyndicate/cve-scores

References

gitlab.com/gitlab-org/gitlab/-/issues/341566 (Broken Link)
hackerone.com/reports/1347600 (Permissions Required, Third Party Advisory)
gitlab.com/gitlab-org/cves/-/blob/master/2021/CVE-2021-39906.json (Vendor Advisory)

Frequently asked questions

What is CVE-2021-39906?: CVE-2021-39906 is a high-severity vulnerability in GitLab, classified under Cross-site Scripting. CVSS score: 8.7/10. Published 2021-11-05.
How severe is CVE-2021-39906?: High severity. CVSS v3 base score is 8.7 out of 10.
Is CVE-2021-39906 known to be exploited?: 1 public proof-of-concept repositories are indexed. Not currently listed in the CISA KEV catalog.