Vulnerability · Published Sep 7, 2026 · Assigned by VulnCheck

CVE-2026-86428commonmark 1.5.0 before 2.10.0 Denial of Service via Attributes

High 7.5

In plain English

A high-severity security flaw in commonmark from thephpleague. There are no confirmed reports of exploitation so far. The chance it is exploited in the next 30 days is estimated at 0.5% (higher than 43% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.

Severity (CVSS 3.1)7.5High

Exploit odds (30 days)0.5%top 57.4% of all CVEs

Exploited in the wildNo reportsCISA SSVC: none

Attack toolingNoneno public tooling known

Official description

commonmark versions from 1.5.0 before 2.10.0 contain a denial of service vulnerability in the AttributesExtension when processing distinctly-named attributes. Attackers can submit Markdown with numerous distinct attribute names to cause quadratic-time attribute merging and filtering, consuming disproportionate CPU resources and preventing legitimate requests from completing.

Affected packages & fixed versions

Ecosystem	Package	Fixed in	Advisory
Debian:12	php-league-commonmark	no fix listed	DEBIAN-CVE-2026-86428
Debian:13	php-league-commonmark	no fix listed	DEBIAN-CVE-2026-86428
Debian:14	php-league-commonmark	2.10.0-1	DEBIAN-CVE-2026-86428
Packagist	league/commonmark	2.10.0	GHSA-8rr7-cvq3-gmfh
Ubuntu:26.04:LTS	php-league-commonmark	no fix listed	UBUNTU-CVE-2026-86428

Affected products (as reported)

Vendor	Product	Versions
thephpleague	commonmark	1.5.0 – before 2.10.0

Weakness: CWE-407 · Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

References

GitHub Security Advisory (GHSA-8rr7-cvq3-gmfh) vendor-advisory
VulnCheck Advisory: commonmark 1.5.0 before 2.10.0 Denial of Service via Attributes third-party-advisory