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[GHSA] GHSA-mh25-x5hq-wrqp (high) — league/commonmark: Denial of service via colliding heading slugs

medgithub_advisoriesPublished 2026-08-06

GHSA-mh25-x5hq-wrqp Severity: high CVE: None

league/commonmark: Denial of service via colliding heading slugs

### Impact

`UniqueSlugNormalizer::normalize()` makes each slug document-unique by searching for an unused numeric suffix, but **restarts that search from `1` on every collision**. The k-th heading that collapses to the same base slug performs k−1 array lookups, so K colliding slugs cost

Original source: https://github.com/advisories/GHSA-mh25-x5hq-wrqp