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CVE-2026-86429: commonmark

Severity

8.7 (HIGH)

Vendor

THEPHPLEAGUE

Affected versions

1.5.0 through before 2.9.1

Fixed version

2.9.1

Patch status

Patched

Published

2026-09-07T13:20:42.180

Modified

2026-09-07T13:20:42.180

Why it matters

This matters because the affected product may be exploitable without valid credentials. Internet-facing deployments should be reviewed first.

Recommended admin actions

• Review and patch based on exposure, asset criticality, and business impact.
• Treat internet-facing systems as higher priority.

Technical summary

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.

View the official NVD record for CVE-2026-86429

CVE data is sourced from NVD/CNA records and optional enrichment. Validate against the vendor advisory before taking production action.