Description
league/commonmark is a PHP library for parsing and rendering CommonMark Markdown. From 0.6.0 until 2.9.0, specially crafted Markdown lines can cause the parser to have quadratic time complexity when converting, because several parsing paths repeatedly rescan growing portions of a line to translate between character positions and byte positions, and the Autolink extension can also copy and validate the remaining line at every URL-like prefix, allowing an attacker who can submit Markdown for conversion to consume disproportionate CPU time with a comparatively small request. This issue is fixed in 2.9.0.
References5
- github.com/thephpleague/commonmark/commit/a6ef6cdc308dfa39a3423…
- github.com/thephpleague/commonmark/commit/a70979ea0d7d3377bd712…
- github.com/thephpleague/commonmark/commit/c97b02e5e652b992033b9…
- github.com/thephpleague/commonmark/releases/tag/2.9.0
- github.com/thephpleague/commonmark/security/advisories/GHSA-2q4…
Metrics
- CVSS 3.1
-
7.5
HIGH
Score source: CNA
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H - EPSS — exploit probability
- 1% percentile: 51 · as of 12 November 2026
- CWE
- CWE-407CWE-1050
Could this be exploited in your environment?
A patch closes the known hole. A penetration test shows what an attacker can still reach — with proof.