CVE-2026-86435: Inefficient Algorithmic Complexity in thephpleague commonmark
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.
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 an attacker to create documents with duplicate footnotes and references. This triggers quadratic output expansion, which consumes excessive server memory and CPU, potentially leading to resource exhaustion and denial of service.
Potential Impact
Exploitation of this vulnerability can cause denial of service by exhausting server resources such as memory and CPU due to quadratic output expansion when processing crafted documents with duplicate footnotes. This can disrupt availability of services relying on thephpleague commonmark library.
Mitigation Recommendations
Patch status is not yet confirmed — check the vendor advisory for current remediation guidance. Until an official fix is available, consider implementing input validation or limiting document complexity to mitigate potential denial of service.
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: 09/15/2026, 00:36:19 UTC
Last updated: 10/07/2026, 18:48:24 UTC
Views: 68
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