commonmark before 2.9.1 Denial of Service via SmartPunct and Attributes
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.
CVE-2026-86429
Primary source · Revision 1
Imported from structured advisory data. Source references identify upstream records or fields; verify affected versions and your deployed configuration.
Security context
Source reference: cve:CVE-2026-86429
commonmark
Source reference: /containers/cna/affected/0/product
- Affected versions
- Not stated in this record
- Fixed versions
- Not stated in this record
- Prerequisites
- Not stated in this record
Structured affected-version data
Original package identities and version rules from this source.
[
{
"vendor": "thephpleague",
"product": "commonmark",
"versions": [
{
"status": "affected",
"version": "1.5.0",
"lessThan": "2.9.1",
"versionType": "semver"
},
{
"status": "unaffected",
"version": "2.9.1",
"versionType": "semver"
}
],
"packageURL": "pkg:composer/league/commonmark",
"defaultStatus": "unaffected"
}
]- Related CVEs
- CVE-2026-86429
Source reference:
/cveMetadata/cveId
Publisher severity
high
Source reference: /containers/cna/metrics
- Event
- #12946 · Revision 1
- Added to Heist Feed
- Publisher date