CVE-2026-86428

commonmark versions from 1.5.0 before 2.10.0 contain a denial of service vulnerability in the AttributesExtension when processing distinctly-named attributes. Attackers can submit Markdown with numerous distinct attribute names to cause quadratic-time attribute merging and filtering, consuming disproportionate CPU resources and preventing legitimate requests from completing.

  • Published Sep 7, 2026
  • CVSS 8.7 high
  • 0.5% chance of exploitation in the next 30 days (EPSS)
  • A fix is available

Affected software

CVE-2026-86428 at the National Vulnerability Database