| Name | CVE-2026-86434 |
| Description | 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. |
| Source | CVE (at NVD; CERT, ENISA, LWN, oss-sec, fulldisc, Debian ELTS, Red Hat, Ubuntu, Gentoo, SUSE bugzilla/CVE, GitHub advisories/code/issues, web search, more) |
The table below lists information on source packages.
| Source Package | Release | Version | Status |
|---|---|---|---|
| php-league-commonmark (PTS) | bookworm | 2.3.9-1+deb12u1 | vulnerable |
| trixie | 2.7.0-1+deb13u1 | vulnerable | |
| forky, sid | 2.10.0-1 | fixed |
The information below is based on the following data on fixed versions.
| Package | Type | Release | Fixed Version | Urgency | Origin | Debian Bugs |
|---|---|---|---|---|---|---|
| php-league-commonmark | source | (unstable) | 2.9.0-1 |
https://github.com/thephpleague/commonmark/security/advisories/GHSA-mh25-x5hq-wrqp
Fixed by: https://github.com/thephpleague/commonmark/commit/6cfa16c7f37e2748114c56d9375a09af656b995c (2.9.0)