CVE-2026-86429: high-severity vulnerability in thephpleague commonmark
commonmark before 2.9.1 Denial of Service via SmartPunct and Attributes
Published · Updated
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21Vexday Risk Score
No sign of exploitation. No public exploitation artifact known so far.
ssvc Trackcvss 8.7epss 0.5%
The league/commonmark (thephpleague/commonmark) library in versions >= 1.5.0 and < 2.9.1 contains quadratic parsing complexity in its SmartPunctExtension and AttributesExtension. When either extension is explicitly registered on the Environment (they are not enabled by default and are excluded from the standard CommonMark and GitHub-Flavored Markdown converters), an unauthenticated attacker can submit small, specially crafted Markdown documents — such as text alternating with unpaired quotes, contiguous runs of block-level attribute blocks, or repeated class attributes — to trigger disproportionate CPU consumption and cause a denial of service. Fixed in 2.9.1.
CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N
Affected products
thephpleague · commonmarkRelated CVEs — thephpleague commonmark
In the same product, most dangerous first.
CVE-2026-71488HIGHleague/commonmark: Quadratic-time denial of service when parsing crafted MarkdownEPSS 0.6%CVE-2026-86434HIGHcommonmark 2.0.0 through 2.8.3 Denial of Service via Slug CollisionEPSS 0.5%CVE-2026-86433HIGHcommonmark 1.5.0 before 2.8.4 Denial of Service via AttributesEPSS 0.5%CVE-2026-86430HIGHleague/commonmark before 2.9.1 Denial of Service via parsingEPSS 0.5%CVE-2026-86428HIGHcommonmark 1.5.0 before 2.10.0 Denial of Service via AttributesEPSS 0.5%CVE-2024-58382HIGHleague/commonmark before 2.6.0 Denial of Service via Quadratic ComplexityEPSS 0.5%