CVE-2026-86428: Inefficient Algorithmic Complexity in thephpleague commonmark
Description
Thephpleague commonmark versions from 1.5.0 up to but not including 2.10.0 contain a denial of service vulnerability due to inefficient algorithmic complexity in the AttributesExtension. This flaw allows attackers to submit Markdown with many distinct attribute names, causing quadratic-time processing that consumes excessive CPU resources and disrupts legitimate requests.
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
CVE-2026-86428 is a denial of service vulnerability in thephpleague commonmark's AttributesExtension affecting versions >=1.5.0 and <2.10.0. The vulnerability arises from quadratic-time attribute merging and filtering when processing Markdown containing numerous distinct attribute names. This inefficiency can be exploited by attackers to exhaust CPU resources, leading to service disruption.
Potential Impact
Exploitation of this vulnerability results in denial of service by consuming disproportionate CPU resources during Markdown processing. This prevents legitimate requests from completing, potentially causing service outages or degraded performance.
Mitigation Recommendations
Patch status is not yet confirmed — check the vendor advisory for current remediation guidance. Until an official fix is available, consider limiting the size and complexity of Markdown inputs or implementing resource usage controls to mitigate impact.
Technical Details
- Data Version
- 5.2
- Assigner Short Name
- VulnCheck
- Date Reserved
- 2026-09-07T12:33:13.368Z
- Cvss Version
- 4.0
- State
- PUBLISHED
Threat ID: 6a9eb72cacd9273b49a9cf70
Added to database: 09/07/2026, 13:07:56 UTC
Last enriched: 10/09/2026, 21:25:06 UTC
Last updated: 10/23/2026, 01:15:27 UTC
Views: 58
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