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GitLabApplication

CVE-2021-39938

MEDIUM · 6.5 CVSS v3.1 Published 2021-12-13
Fix available
A fix is available. Upgrade to 14.3.6 / 14.4.4 or later.
See remediation →
71/100
Remediation priority · Elevated
Remotely reachable Zero-click

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
A vulnerable regular expression pattern in GitLab CE/EE since version 8.15 before 14.3.6, all versions starting from 14.4 before 14.4.4, all versions starting from 14.5 before 14.5.2, allows an attacker to cause uncontrolled resource consumption leading to Denial of Service via specially crafted deploy Slash commands

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 · high confidence

ReDoS (Regular Expression Denial of Service) vulnerability in GitLab's deploy Slash command processing. A specially crafted regex pattern in the slash command parser allows attacker-controlled input to cause catastrophic backtracking, consuming excessive CPU and memory leading to service unavailability.

MitigationUpgrade GitLab to version 14.3.6, 14.4.4, 14.5.2 or later. As a compensating control, implement input validation and length limits on slash command parameters until patching is completed.

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:>= 8.15.0, < 14.3.6>= 14.4.0, < 14.4.4>= 14.5.0, < 14.5.2

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
Low
User interaction
None
Scope
Unchanged
Confidentiality
None
Integrity
None
Availability
High

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

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
    Access the GitLab Admin Area via /admin/application_settings or run 'gitlab-rake gitlab:env:info' on the server to retrieve the exact version number
    Affected if The installed version falls within: >= 8.15.0 and < 14.3.6; OR >= 14.4.0 and < 14.4.4; OR >= 14.5.0 and < 14.5.2
  2. Confirm slash command processing is enabled
    Navigate to Admin Area > Settings > Repository > GitLab Flavored Markdown and verify that 'Slash commands' option is enabled (this is enabled by default in most installations)
    Affected if Slash commands are enabled and the GitLab version is in the affected ranges listed above

If the installed GitLab version matches any of the affected version ranges AND slash command processing is enabled, the environment is vulnerable to this ReDoS flaw.

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 14.3.6 / 14.4.4 / 14.5.2 or later
Fixed in 14.3.614.4.414.5.2
Interim mitigation

Upgrade GitLab to version 14.3.6, 14.4.4, 14.5.2 or later. As a compensating control, implement input validation and length limits on slash command parameters until patching is completed.

Recommended fix High confidence

14.3.6, 14.4.4, or 14.5.2 (minimum, depending on your current version branch; consider latest 14.x for additional fixes)

  1. 1. Identify your current GitLab version by checking the GitLab admin area or running `cat /opt/gitlab/version.rb`
  2. 2. Create a full backup of your GitLab instance using `gitlab-backup-create` or the omnibus backup command
  3. 3. If your current version is >= 8.15.0 and < 14.3.6, upgrade to version 14.3.6 or later
  4. 4. If your current version is >= 14.4.0 and < 14.4.4, upgrade to version 14.4.4 or later
  5. 5. If your current version is >= 14.5.0 and < 14.5.2, upgrade to version 14.5.2 or later
  6. 6. After upgrade, verify GitLab is running and check the admin dashboard for any errors
  7. 7. Test that deploy Slash commands work correctly with normal input
Caveat Review GitLab release notes for breaking changes between your current version and target version; major version jumps may require database migrations

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

Fix this in GitLab Scoped from the published advisory
  • Consultation2.0 h
  • Implementation3.0 h
  • Testing3.0 h
  • Review / QA2.0 h
10.0 hours of engineering $1,750
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An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $2,800.

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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-2021-39938 in production — separate from our analysis above.

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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