CVE-2026-115352 lepture CVE debrief

Who should care

Defenders responsible for maintaining and securing systems that use Mistune should assess exposure to potential DoS attacks and prioritize verification of Mistune versions in use. This includes operators, platform administrators, vulnerability management teams, and security teams who need to ensure that Mistune is updated to version 3.3.0 or later to prevent potential system performance and availability impacts.

Why it matters

CVE-2026-115352 is a high-severity vulnerability in Mistune before 3.3.0 that allows unauthenticated attackers to exhaust CPU by submitting long runs of unmatched '[' characters, potentially impacting system performance and availability.

• Potential for CPU exhaustion due to long runs of unmatched '[' characters
• Possible impact on system performance and availability
• Need for verification of Mistune versions in use
• Priority for updating Mistune to version 3.3.0 or later

Technical summary

The inline link parser in Mistune before 3.3.0 contains an algorithmic complexity vulnerability that allows unauthenticated attackers to exhaust CPU by submitting long runs of unmatched '[' characters. This vulnerability can be triggered by small markdown payloads that trigger O(N^2) parse_link_text and parse_link_label probing, occupying rendering workers for 30+ seconds per 16 KB input. Defenders should prioritize verification of Mistune versions in use and assess exposure to potential DoS attacks. No additional technical details are available.

Defensive priority

Defenders should prioritize verification of Mistune versions in use and assess exposure to potential DoS attacks.

Recommended defensive actions

• Verify Mistune versions in use and assess exposure to potential DoS attacks
• Update Mistune to version 3.3.0 or later
• Monitor for potential DoS attacks using long runs of unmatched '[' characters
• 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
• Confirm whether affected product deployments exist in managed environments and assign an owner for follow-up

Evidence notes

The CVE record and source item provide details on the vulnerability in Mistune before 3.3.0, which allows unauthenticated attackers to exhaust CPU by submitting long runs of unmatched '[' characters. Evidence is limited to CVE Program and NVD records. Defenders should verify Mistune versions and assess exposure to potential DoS attacks. No additional evidence or exploit details are available.

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.