CVE-2026-71488

league/commonmark: Quadratic-time denial of service when parsing crafted Markdown

Published Aug 6, 2026 CVSS 3.1 · 7.5 High EPSS < 1% KEV · Not listed
Description
league/commonmark is a PHP library for parsing and rendering CommonMark Markdown. From 0.6.0 until 2.9.0, specially crafted Markdown lines can cause the parser to have quadratic time complexity when converting, because several parsing paths repeatedly rescan growing portions of a line to translate between character positions and byte positions, and the Autolink extension can also copy and validate the remaining line at every URL-like prefix, allowing an attacker who can submit Markdown for conversion to consume disproportionate CPU time with a comparatively small request. This issue is fixed in 2.9.0.

Remediation

No solution or workaround provided in the CVE record

Tracking

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Advisories

Source ID Title
Github GHSA Github GHSA GHSA-2q4p-g7hv-5rgv league/commonmark: Quadratic-time denial of service when parsing crafted Markdown
History
Type Values Removed Values Added
Metrics ssvc

{'options': {'Automatable': 'yes', 'Exploitation': 'none', 'Technical Impact': 'partial'}, 'version': '2.0.3'}

Type Values Removed Values Added
First Time appeared Thephpleague
Thephpleague commonmark
Vendors & Products Thephpleague
Thephpleague commonmark
Type Values Removed Values Added
Description league/commonmark is a PHP library for parsing and rendering CommonMark Markdown. From 0.6.0 until 2.9.0, specially crafted Markdown lines can cause the parser to have quadratic time complexity when converting, because several parsing paths repeatedly rescan growing portions of a line to translate between character positions and byte positions, and the Autolink extension can also copy and validate the remaining line at every URL-like prefix, allowing an attacker who can submit Markdown for conversion to consume disproportionate CPU time with a comparatively small request. This issue is fixed in 2.9.0.
Title league/commonmark: Quadratic-time denial of service when parsing crafted Markdown
Weaknesses CWE-1050
CWE-407
References
Metrics cvssV3_1

{'score': 7.5, 'vector': 'CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H'}

Weaknesses

Sources

Status
PUBLISHED
Assigner
GitHub_M
Published
Updated
Aug 7, 2026, 5:17 PM
Reserved
Aug 6, 2026, 7:56 PM
Status
Awaiting Analysis
Published
Aug 6, 2026, 10:18 PM
Modified
Oct 24, 2026, 3:10 PM