Algorithmic Complexity Affecting php-league-commonmark package, versions <2.9.0-1


Severity

Recommended
0.0
high
0
10

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Threat Intelligence

EPSS
0.51% (41st percentile)

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  • Snyk IDSNYK-DEBIAN14-PHPLEAGUECOMMONMARK-19641662
  • published8 Sept 2026
  • disclosed7 Sept 2026

Introduced: 7 Sep 2026

CVE-2026-86434  (opens in a new tab)
CWE-407  (opens in a new tab)

How to fix?

Upgrade Debian:14 php-league-commonmark to version 2.9.0-1 or higher.

NVD Description

Note: Versions mentioned in the description apply only to the upstream php-league-commonmark package and not the php-league-commonmark package as distributed by Debian. See How to fix? for Debian:14 relevant fixed versions and status.

league/commonmark versions >= 2.0.0 and < 2.8.4 (patched in 2.9.0) contain a denial of service vulnerability in UniqueSlugNormalizer::normalize(), which restarts its numeric-suffix search from 1 on every slug collision, resulting in O(K^2) time complexity for K headings that collapse to the same base slug. The vulnerable path is reached when HeadingPermalinkExtension, FootnoteExtension, or TableOfContentsExtension is registered. An unauthenticated attacker can force many headings onto a single base slug (e.g., via empty ATX headings, identical heading text, or punctuation-only headings) in a small Markdown document, consuming excessive CPU and denying service.

CVSS Base Scores

version 3.1