CVE-2026-86435: Inefficient Algorithmic Complexity in thephpleague commonmark
Description
CVE-2026-86435 is a denial of service vulnerability in thephpleague commonmark's Footnote extension. Versions from 1.5.0 up to but not including 2.8.4 fail to deduplicate footnote definitions, allowing attackers to craft documents with duplicate footnotes that cause quadratic output expansion. This results in excessive memory and CPU consumption, potentially exhausting server resources.
CVSS v4.0
Score 8.7high
Affected software
thephpleague
commonmark
pkg:composer/thephpleague/commonmarkRun on your own infrastructure? Check whether these packages are installed with threat-finder — our free open-source scanner.
AI-Powered Analysis
Machine-generated threat intelligence
Technical Analysis
Thephpleague commonmark versions >=1.5.0 and <2.8.4 contain a denial of service vulnerability in the Footnote extension. The vulnerability arises because the extension does not deduplicate footnote definitions, enabling attackers to create documents with duplicate footnotes and references. This leads to quadratic output expansion, which can consume excessive CPU and memory resources, causing a denial of service condition.
Potential Impact
Successful exploitation can cause the server running the vulnerable commonmark library to consume excessive CPU and memory resources, leading to denial of service by exhausting server capacity. There is no indication of privilege escalation, data leakage, or other impacts.
Mitigation Recommendations
Patch status is not yet confirmed — check the vendor advisory for current remediation guidance. Until a patch is available, avoid processing untrusted documents that may contain crafted duplicate footnote definitions to mitigate risk.
Technical Details
- Data Version
- 5.2
- Assigner Short Name
- VulnCheck
- Date Reserved
- 2026-09-07T12:34:31.457Z
- Cvss Version
- 4.0
- State
- PUBLISHED
Threat ID: 6a9eb72eacd9273b49a9cff0
Added to database: 09/07/2026, 13:07:58 UTC
Last enriched: 10/09/2026, 21:25:38 UTC
Last updated: 10/22/2026, 13:15:24 UTC
Views: 79
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