# CVE-2026-86435

## Summary

- **CVE ID:** CVE-2026-86435
- **Severity:** HIGH
- **CVSS Score:** 8.7 (CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N)
- **CWE:** CWE-407
- **Published:** Sep 7, 2026
- **Last Modified:** Sep 9, 2026

## Description

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.

## Affected Products

- thephpleague — commonmark (1.5.0)
- thephpleague — commonmark (2.8.4)

## References

- [CNA](https://github.com/thephpleague/commonmark/security/advisories/GHSA-jfm3-95jq-q3rf)
- [CNA](https://www.vulncheck.com/advisories/commonmark-1.5.0-before-2.8.4-denial-of-service-via-footnote)

## Exploitation Prediction (EPSS)

- **EPSS Score:** 0.28%
- **EPSS Percentile:** 20.2

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_Exported from OnDuty AI Vulnerability Intelligence on 2026-09-10._