CVE-2026-86433: Inefficient Algorithmic Complexity in thephpleague commonmark
Description
Thephpleague commonmark versions from 1.5.0 up to but not including 2.8.4 contain a denial of service vulnerability in the Attributes extension. This vulnerability arises because the AttributesListener::findTargetAndDirection() function performs quadratic-time scanning of sibling lists. An unauthenticated attacker can exploit this by submitting about 32 KB of repeated attribute blocks, causing the parser to take over 5 seconds and 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
CVE-2026-86433 is a denial of service vulnerability in thephpleague commonmark's Attributes extension affecting versions >=1.5.0 and <2.8.4. The vulnerability is due to inefficient algorithmic complexity in the AttributesListener::findTargetAndDirection() method, which performs quadratic-time scanning of sibling lists. This allows unauthenticated attackers to submit crafted input with repeated attribute blocks (~32 KB) that significantly degrade parsing performance, leading to resource exhaustion and denial of service.
Potential Impact
Successful exploitation results in denial of service by exhausting server resources due to excessive parsing time (over 5 seconds) caused by quadratic-time processing of crafted attribute blocks. The vulnerability requires no authentication and can be triggered remotely, making it a high-severity risk for affected versions.
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 size limits or rate limiting to mitigate potential denial of service attempts targeting the Attributes extension.
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: 09/15/2026, 01:14:22 UTC
Last updated: 10/08/2026, 06:48:20 UTC
Views: 79
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