CVE-2026-86434
HIGHDescription
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 v3 vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Affected routers (0)
No routers currently mapped to this CVE in our database.