CVE-2021-39917Public exploitNetwork attack vector

Authenticated service outage via quick-action regex backtracking

Published Dec 13, 2021 · Updated Aug 4, 2024

Regular expression denial of service in GitLab allows remote authenticated users to make the application unresponsive via crafted issue bodies. The INLINE_CODE_REGEX in lib/gitlab/quick_actions/extractor.rb performs cubic-complexity matching while excluding Markdown from quick-action parsing, so newline-heavy unmatched inline-code input consumes application resources. The affected ranges start at 12.9, 14.4, and 14.5 and end before 14.3.6, 14.4.4, and 14.5.2, respectively; an API token and permission to create issues in one project are required.

CVSS severity6.5
Medium
EPSS probability1.33%
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 allows remote authenticated users to make the application unresponsive via crafted issue bodies. The INLINE_CODE_REGEX in lib/gitlab/quick_actions/extractor.rb performs cubic-complexity matching while excluding Markdown from quick-action parsing, so newline-heavy unmatched inline-code input consumes application resources. The affected ranges start at 12.9, 14.4, and 14.5 and end before 14.3.6, 14.4.4, and 14.5.2, respectively; an API token and permission to create issues in one project are required.

The record

CVE
CVE-2021-39917
Published
Dec 13, 2021
Updated
Aug 4, 2024
Vendor
GitLab
Product
GitLab
Classifications
CWE-697, 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=>=12.9, <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=>=12.9, <14.3.6; version=>=14.4, <14.4.4; version=>=14.5, <14.5.2

Published CVSS scores

6.5NIST NVDCVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H

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.

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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-697Incorrect Comparison
T1499.004Application 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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