CVE-2026-86435
HighCVSS 7.5Summary
Denial of service vulnerability in the Footnote extension of commonmark versions from 1.5.0 before 2.8.4. Lack of deduplication of footnote definitions allows attackers to craft documents with duplicates, leading to quadratic output expansion and excessive memory and CPU consumption.
Risk Assessment
An attacker can exhaust server resources, causing service unavailability for other users.
Recommendation
Update the commonmark library to version 2.8.4 or later, which includes the fix.
Other vulnerabilities in commonmark
See all- CVE-2026-86433High
Denial of service vulnerability in the Attributes extension of commonmark versions from 1.5.0 before 2.8.4. AttributesListener::findTargetAndDirection() performs quadratic-time sibling list scanning. Unauthenticated attackers can submit approximately 32 KB of repeated attribute blocks to cause parsing to take over 5 seconds, exhausting server resources.
- CVE-2026-86432Medium
commonmark versions from 2.0.0 before 2.8.4 contain a denial of service vulnerability in XmlRenderer that emits depth-proportional indentation for every XML tag. Attackers can provide deeply nested Markdown or AST structures to cause quadratic memory consumption and output amplification, exhausting server resources.
- CVE-2026-86428High
Denial of service vulnerability in commonmark versions from 1.5.0 before 2.10.0 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.
Original NVD description (English source)
commonmark versions from 1.5.0 before 2.8.4 contain a denial of service vulnerability in the Footnote extension that fails to deduplicate footnote definitions. Attackers can craft documents with duplicate footnote definitions and references to create quadratic output expansion, consuming excessive memory and CPU to exhaust server resources.