CVE-2026-86435

High

Description

commonmark versions from 1.5.0 before 2.8.4 contain a denial of service vulnerability in the Footnote extension that fails to deduplicate footnote definitions. Attackers can craft documents with duplicate footnote definitions and references to create quadratic output expansion, consuming excessive memory and CPU to exhaust server resources.

SeverityHigh

CVSS7.5

Exploit probability—

ProductThephpleague Commonmark

PublishedSep 7, 2026

First seenSep 7, 2026

Weakness typeCWE-407CWE-407

How to fix

Update

thephpleague commonmark2.8.4 or later

Vendor advisories

github.com/thephpleague/commonmark/security/advisories/GHSA-jfm3-95jq-q3rf

Affected products

Product	Affected versions	Fixed in
thephpleague commonmark	1.5.0 ≤ v < 2.8.4	2.8.4

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