CVE-2026-86433: Inefficient Algorithmic Complexity in thephpleague commonmark
Description
CVE-2026-86433 is a denial of service vulnerability in thephpleague commonmark's Attributes extension affecting versions from 1.5.0 up to but not including 2.8.4. The vulnerability arises from an inefficient quadratic-time algorithm in AttributesListener::findTargetAndDirection(), which can be exploited by unauthenticated attackers submitting repeated attribute blocks to exhaust server resources and cause parsing delays exceeding 5 seconds.
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 due to an inefficient algorithmic complexity in the Attributes extension. Specifically, the AttributesListener::findTargetAndDirection() method performs sibling list scanning in quadratic time. An unauthenticated attacker can exploit this by submitting approximately 32 KB of repeated attribute blocks, causing the parser to consume excessive CPU time and delay processing for over 5 seconds, leading to resource exhaustion.
Potential Impact
This vulnerability allows unauthenticated attackers to cause a denial of service by exhausting server resources through specially crafted input that triggers quadratic-time parsing behavior. This can degrade service availability and potentially disrupt operations relying on the commonmark parser.
Mitigation Recommendations
The vulnerability affects versions >=1.5.0 and <2.8.4. Users should upgrade to version 2.8.4 or later where this issue is fixed. Patch status is not explicitly confirmed in the provided data, so verify the vendor advisory for official remediation details. No cloud service is involved, so remediation depends on updating the affected software.
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: 6a9eb72eacd9273b49a9cfec
Added to database: 09/07/2026, 13:07:58 UTC
Last enriched: 10/09/2026, 21:25:31 UTC
Last updated: 10/21/2026, 13:20:24 UTC
Views: 91
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