league/commonmark: Quadratic-time denial of service in the GitHub Flavored Markdown Table extension block-start scan
High · CVSS 7.5
## Summary `league/commonmark`'s GitHub Flavored Markdown Table extension registers `TableStartParser` as a block-start parser. While a paragraph is the active block, the core block parser calls `TableStartParser::tryStart()` on every non-blank line. Its first action fetches the entire growing paragraph buffer via `getParagraphContent()` and runs `strpos($paragraph, '|')` across all of it. For a paragraph of M pipe-free lines, line k rescans about k lines of buffer, so total work is 1+2+...+M, which is O(M^2).
Remediation
Upgrade league/commonmark to 2.10.2 or later.
Affected PHP branches
See the source advisory.
Source: GitHub Global Security Advisories (Composer ecosystem) · retrieved 2026-10-22T10:19:14-04:00 · https://github.com/advisories/GHSA-3q6v-r5mr-hxv8