Intel

AIKIDO-2026-176089

league/commonmark is vulnerable to Denial of Service (DoS)

Denial of Service (DoS)GHSA-mj63-m3rc-8ppr Published Aug 5, 2026

53

Medium Risk

This Affects:

PHPleague/commonmark
2.0.0 - 2.8.3
Fixed in 2.9.0
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TL;DR

The XML renderer pretty-prints output by emitting indentation whitespace proportional to each element's nesting depth for every opening and closing tag. For a deeply nested document tree the indentation alone sums to a quadratic number of bytes of output and memory. Converting untrusted Markdown to XML, such as a single line of deeply nested blockquotes, can amplify a small request into a very large response and exhaust memory. The fix caps indentation depth with a configurable maximum so output size grows in proportion to input.

Who does this affect?

You are affected if you are using a version that falls within the vulnerable range and you convert untrusted Markdown to XML output.

Background info

league/commonmark is vulnerable to Denial of Service (DoS) in versions 2.0.0 - 2.8.3.

How to fix this

Upgrade the league/commonmark library to the patch version.

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