High 7.5Published Sep 7, 2026

CVE-2026-86429commonmark before 2.9.1 Denial of Service via SmartPunct and Attributes

Updated under an hour ago (2026-10-19 10:00 UTC)

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It affects thephpleague commonmark. Add what you run to find out whether that includes you.

No exploitation reported and no EPSS estimate yet.

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Every CVE for thephpleague commonmark

Exploited in the last 30 days

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: 7.5 HIGH (v3.1, CNA)CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Weakness (CWE): CWE-407
Known exploited: Not in CISA's KEV catalog
EPSS (exploitation in the next 30 days): Not loaded for this CVE
Assigned by: VulnCheck
NVD analysis: Analyzed
Record last updated: Oct 8, 2026
First seen by InfoSec Signals: Oct 9, 2026

Affected products

Affected products

thephpleague commonmark thephpleague:commonmark (from the name)	from 1.5.0 before 2.9.1; 2.9.1 not affected	CNA record
thephpleague commonmark thephpleague:commonmark	from 1.5.0 before 2.9.1	NVD

References

https://github.com/thephpleague/commonmark/security/advisories/GHSA-jjv6-8j6v-6j52vendor-advisory
https://www.vulncheck.com/advisories/commonmark-before-2.9.1-denial-of-service-via-smartpunct-and-attributesthird-party-advisory

The CVE record on cve.org NVD's entry

The CVE record is authoritative. Products marked “from the name” were identified from the CNA's free-text names, not a CPE, and are matched less certainly. This product uses the NVD API but is not endorsed or certified by the NVD.