CVE-2026-105830 thephpleague CVE debrief

Who should care

Developers and administrators responsible for maintaining systems that use the league/commonmark library should assess their exposure and prioritize patching or mitigating this vulnerability to prevent potential DoS attacks.

Why it matters

CVE-2026-105830 is a high-severity vulnerability in the league/commonmark library that can lead to denial of service attacks. Defenders should prioritize patching or mitigating this vulnerability to prevent potential DoS attacks.

• Potential exhaustion of PHP worker CPU, leading to denial of service
• Increased risk of system crashes or performance degradation
• Potential impact on system availability and responsiveness

Technical summary

The league/commonmark library, affecting versions from 2.0.0 before 2.10.2, contains a quadratic-time denial of service vulnerability in the GitHub Flavored Markdown Table extension's TableStartParser::tryStart() block-start scan. An unauthenticated attacker can submit a large paragraph of pipe-free lines not starting with letters, forcing repeated full-buffer strpos scans that exhaust PHP worker CPU.

Defensive priority

Defenders should prioritize patching or mitigating this vulnerability to prevent potential DoS attacks. This requires immediate attention from developers and administrators responsible for maintaining systems that use the league/commonmark library.

Recommended defensive actions

• Patch or upgrade to version 2.10.2 or later
• Implement input validation and sanitization to prevent large paragraphs of pipe-free lines
• Monitor system performance and CPU usage for potential DoS attacks
• Consider using a Web Application Firewall (WAF) to detect and prevent suspicious traffic
• Review compensating controls for exposed systems while remediation is scheduled and verified
• Check relevant monitoring, detection, and logs for exposed assets that need extra review
• Track exceptions, retest remediated assets, and close the item only after evidence is documented.

Evidence notes

The vulnerability is confirmed by the CVE Program and NVD. The source item provides detailed information about the vulnerability, including its impact and affected versions. Additional information is available from the vendor's security advisory and a third-party advisory.

Sources and references

Methodology and review provenance

AI-assisted synthesis based on stored public vulnerability evidence. System validation, approval state, and publication status do not by themselves establish human review of this revision. PatchSiren helps prioritize defensive review and does not prove exposure or remediation on any system.