CVE-2021-39933Public exploitNetwork attack vector

Application-wide service hang via regex backtracking

Published Dec 13, 2021 · Updated Aug 4, 2024

Regular expression denial of service in GitLab CE/EE allows remote authenticated users to make an instance unresponsive with crafted content. The PATTERN expression in lib/gitlab/front_matter.rb applies adjacent whitespace quantifiers while parsing front matter from notes, issues, and comments, causing cubic backtracking on a long unterminated block. Project access and an authenticated session or API token are required; repeated submissions can consume backend CPU and hang the application for other users.

CVSS severity4.2
Medium
EPSS probability1.42%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Regular expression denial of service in GitLab CE/EE allows remote authenticated users to make an instance unresponsive with crafted content. The PATTERN expression in lib/gitlab/front_matter.rb applies adjacent whitespace quantifiers while parsing front matter from notes, issues, and comments, causing cubic backtracking on a long unterminated block. Project access and an authenticated session or API token are required; repeated submissions can consume backend CPU and hang the application for other users.

The record

CVE
CVE-2021-39933
Published
Dec 13, 2021
Updated
Aug 4, 2024
Vendor
GitLab
Product
GitLab
Classifications
CWE-1333, CAPEC-492, T1499.004
Attack vector
network
Privileges
authenticated

Timeline

How it unfolded

  1. Dec 13, 2021CVE publishedPublication date reported by the CVE source.
  2. Aug 4, 2024Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=>=12.10, <14.3.6
  2. Affected versionversion=>=14.4, <14.4.4
  3. Affected versionversion=>=14.5, <14.5.2

What conditions does exploitation require?

Attack vectornetwork
Required privilegesauthenticated

What is affected?

GitLab · GitLabversion=>=12.10, <14.3.6; version=>=14.4, <14.4.4; version=>=14.5, <14.5.2

Published CVSS scores

6.5NIST National Vulnerability DatabaseCVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
4.2GitLab Inc.CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:L

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesauthenticated
Known exploitationUnconfirmed
Public exploitPublished

Weakness, pattern, technique

CWE-1333Inefficient Regular Expression Complexity
CAPEC-492Regular Expression Exponential Blowup
T1499.004Endpoint Denial of Service: Application or System Exploitation

Public exploit references

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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