TI-2026-59137 Aliases CVE-2026-86429 GHSA-7x8h-jg2x-pjm5

commonmark before 2.9.1 Denial of Service via SmartPunct and Attributes

MEDIUM 44CWE-407Published 2026-09-07 · Updated 2026-10-08

Key facts

Attack vector: Network
Privileges required: None
User interaction: None
Attack complexity: Low
Attack requirements: None
Impact type: Denial of service
Confidentiality · integrity · availability: None · None · High
Fix status: Fixed

Attack profile from CVSS 4.0 · CNA. Fix status from CNA. Impact type from CWE-407.

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.

Why it matters now

Exploitation None reported CISA SSVC · not in CISA KEV

EPSS 0.00515 44th percentileScored 2026-11-07

Fix Fixed commonmark (thephpleague): 2.9.1

SSVC decision points

CISA ADP · SSVC 2.0.3

Exploitation: None
Automatable: Yes
Technical impact: Partial

The decision (Track, Attend, Act) also depends on your mission and well-being impact; see CISA's SSVC guide.

Affected products

Vendor	Product	Affected versions	Fixed in	Status	Source
thephpleague	commonmark	1.5.0 to before 2.9.1	2.9.1	Patch available	CNA

commonmark Vendorthephpleague Affected 1.5.0 to before 2.9.1 Fixed in 2.9.1 Patch available CNA

CPE configurations NVD · 1

CPE	Versions	Role	Vendor
cpe:2.3:a:thephpleague:commonmark::::::::	1.5.0 to before 2.9.1	Vulnerable	thephpleague

cpe:2.3:a:thephpleague:commonmark:*:*:*:*:*:*:*:* Versions 1.5.0 to before 2.9.1 Vulnerable ·thephpleague

Remediation

Fix · CNA commonmark (thephpleague) Fixed in 2.9.1

Fixed in the same release

Records fixed by the same vendor advisory or release, as the CNA lists them.

Release · 2026-09-07
thephpleague commonmark 2.9.1
3 records Highest priority Priority MEDIUM 2 MEDIUM, 1 LOW
Other records, highest priority first
- TI-2026-59138 league/commonmark before 2.9.1 Denial of Service via parsingPriority MEDIUM 44
- TI-2026-59139 commonmark before 2.9.1 XSS via AttributesExtension form feed bypassPriority LOW 37
Show all 3 records →

Timeline

2026-10-02 Threatist record created from CVE-2026-86429
2026-10-03 Alias added: GHSA-7x8h-jg2x-pjm5

References

Advisory 1

GitHub Security Advisory (GHSA-jjv6-8j6v-6j52)

TI-2026-59138 league/commonmark before 2.9.1 Denial of Service via parsing CVSS 4.0HIGH 8.7
TI-2026-59136 commonmark 1.5.0 before 2.10.0 Denial of Service via Attributes CVSS 4.0HIGH 8.7
TI-2026-59139 commonmark before 2.9.1 XSS via AttributesExtension form feed bypass CVSS 4.0MEDIUM 6.9
TI-2026-25753 league/commonmark has an embed extension allowed_domains bypass CVSS 4.0MEDIUM 6.3
TI-2018-14605 Cross-site scripting (XSS) vulnerability in the PHP League CommonMark library versions… CVSS 3.0MEDIUM 6.1
TI-2019-07346 Cross-site scripting (XSS) vulnerability in the PHP League CommonMark library before… CVSS 3.0MEDIUM 6.1

See all 7 →

Sources

This product uses the NVD API but is not endorsed or certified by the NVD. Sources and licences