Vulnerability · Published Sep 7, 2026 · Assigned by VulnCheck

CVE-2026-86432commonmark 2.0.0 before 2.8.4 Denial of Service via XML

Medium 5.3

In plain English

A medium-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 0.4% (higher than 36% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.

Severity (CVSS 3.1)5.3Medium

Exploit odds (30 days)0.4%top 63.7% of all CVEs

Exploited in the wildNo reportsCISA SSVC: none

Attack toolingNoneno public tooling known

Official description

commonmark versions from 2.0.0 before 2.8.4 contain a denial of service vulnerability in XmlRenderer that emits depth-proportional indentation for every XML tag. Attackers can provide deeply nested Markdown or AST structures to cause quadratic memory consumption and output amplification, exhausting server resources.

Affected packages & fixed versions

Ecosystem	Package	Fixed in	Advisory
Debian:12	php-league-commonmark	no fix listed	DEBIAN-CVE-2026-86432
Debian:13	php-league-commonmark	no fix listed	DEBIAN-CVE-2026-86432
Debian:14	php-league-commonmark	2.9.0-1	DEBIAN-CVE-2026-86432
Ubuntu:26.04:LTS	php-league-commonmark	no fix listed	UBUNTU-CVE-2026-86432

Affected products (as reported)

Vendor	Product	Versions
thephpleague	commonmark	2.0.0 – before 2.8.4

Weakness: CWE-405 · Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L

References

GitHub Security Advisory (GHSA-mj63-m3rc-8ppr) vendor-advisory
VulnCheck Advisory: commonmark 2.0.0 before 2.8.4 Denial of Service via XML third-party-advisory