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GitLabApplication

CVE-2021-39906

MEDIUM · 6.1 CVSS v3.1 Published 2021-11-05
Fix available
A fix is available. Upgrade to 14.2.6 / 14.3.4 or later.
See remediation →
68/100
Remediation priority · Elevated
High EPSS Remotely reachable No privileges

Official description Straight from the sourceThe vendor's or NVD's own wording, published unedited. Authoritative, but often terse — it says what broke, rarely what to do.

NVD · unedited
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.

Technical summary Written by usOur analysis, written from the advisory, the CVSS vector and the affected-version data. It adds context the advisory leaves out, and never invents facts that are not in the source.

dbcve analysis · moderate confidence

GitLab CE/EE versions 13.5 and above fail to properly validate Jupyter notebook (.ipynb) file uploads, allowing malicious JavaScript code to be embedded within the JSON structure of the notebook file. When victims view or interact with these crafted files in GitLab's web interface, the embedded JavaScript executes in their browser context, leading to stored XSS.

MitigationUpgrade GitLab to the patched version (consult GitLab's security release notes for the fix version). Alternatively, restrict or disable ipynb file uploads in project settings until patching is feasible.

Verify against the referenced sources before acting — the references below are authoritative for this CVE, this summary is not.

Affected products & versions What the vendor confirmedThe version ranges the vendor confirmed as vulnerable. If your version sits inside a range here, treat yourself as exposed until you have upgraded.

NVD · CPE data
GitLabApplication
Affected:>= 13.5.0, < 14.2.6>= 14.3.0, < 14.3.4>= 14.4.0, < 14.4.1

CVSS breakdown How the score is builtThe industry scoring standard. It rates how the flaw is reached, what it takes to exploit, and what an attacker gains — the score is derived from those, not the other way round.

From the vector
Attack vector
Network
Complexity
Low
Privileges
None
User interaction
Required
Scope
Changed
Confidentiality
Low
Integrity
Low
Availability
None

CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N

Am I affected? How to checkSteps we derive from the advisory and the affected-version data, so you can decide whether this CVE reaches your setup. They are a guide, not a scan — your own configuration is the authority.

dbcve checks

Work through these to decide whether this CVE applies to you.

  1. Check installed GitLab version
    Run 'gitlab-rake gitlab:env:info' or view /opt/gitlab/version.txt to see the exact version running
    Affected if Version is 13.5.0 through 14.2.5, 14.3.0 through 14.3.3, or 14.4.0
  2. Identify repositories with .ipynb files
    Search repositories using GitLab API or UI for files with .ipynb extension: go to project -> repository -> search for '*.ipynb' or use API endpoint /projects/:id/repository/tree?recursive=true&per_page=100
    Affected if Any .ipynb files exist in repositories and GitLab version is vulnerable
  3. Verify Jupyter notebook preview is accessible
    Attempt to view a .ipynb file in the GitLab web interface by navigating to the file in a browser - the XSS triggers when the file is rendered in the web UI
    Affected if Web interface is accessible and renders .ipynb files directly in browser
  4. Check if file uploads are permitted
    Review GitLab project settings at Project -> Settings -> General -> Visibility, project features, permissions to confirm repository and file upload capabilities are enabled
    Affected if Users can upload files to repositories in the affected version

Environment is affected if running a vulnerable GitLab version (13.5.0-14.2.5, 14.3.0-14.3.3, or 14.4.0) AND users can upload/view .ipynb files in the web interface, as the XSS executes when the notebook JSON is rendered in the browser.

Generated from the published advisory. Verify against your own configuration.

Check your environment

Paste your version and any relevant configuration and it will be compared against the affected criteria above. Do not include secrets or credentials.

AI-assisted, checked against the advisory. Informational, not a guarantee.

Remediation Closing itWhat it takes to close this. Where a vendor fix exists we point at it; where none exists we say so plainly, and can build one. Effort estimates are scoped from the advisory, not from your codebase.

dbcve · scoped
Upgrade available Upgrade to 14.2.6 / 14.3.4 / 14.4.1 or later
Fixed in 14.2.614.3.414.4.1
Interim mitigation

Upgrade GitLab to the patched version (consult GitLab's security release notes for the fix version). Alternatively, restrict or disable ipynb file uploads in project settings until patching is feasible.

Recommended fix High confidence

14.4.1 or later ( alternatively: 14.2.6+, 14.3.4+)

  1. Back up your GitLab instance data and configuration
  2. Update your GitLab package repository to fetch the latest packages
  3. Stop GitLab services (gitlab-ctl stop)
  4. Install the updated GitLab package (e.g., apt-get install gitlab-ee or gitlab-ce depending on your edition)
  5. Reconfigure GitLab (gitlab-ctl reconfigure)
  6. Restart GitLab services (gitlab-ctl start)
  7. Verify the upgrade was successful by checking the GitLab version

Generated from the published advisory — verify against the referenced sources before acting.

Fix this in GitLab Scoped from the published advisory
  • Consultation3.0 h
  • Implementation6.0 h
  • Testing4.0 h
  • Review / QA2.0 h
15.0 hours of engineering $2,640
Get the upgrade done

An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $4,224.

Scan for this in your stack

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References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.

Primary sources

Practitioner notes

Contributed

Peer-ranked notes from engineers who’ve handled CVE-2021-39906 in production — separate from our analysis above.

No notes yet

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What this is

A place for practitioners to share what actually worked: a mitigation you’ve tested, a configuration change, a version- or environment-specific caveat, or a link to a verified patch. The most useful notes rise to the top as peers upvote them, so the signal stays high.

What belongs here
  • Verified mitigations, workarounds, and config changes
  • Version or environment caveats, and links to real fixes
  • No weaponised exploit code, or anything meant to cause harm
  • No spam, self-promotion, credentials, or personal data