CVE-2026-115352: Mistune before 3.3.0 Quadratic-Time DoS via Unmatched Brackets in Inline Parser

Severity: high (CVSS 7.5 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.4% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2026-10-22 · updated 2026-10-23
Weakness: CWE-407

Description

Mistune before 3.3.0 contains an algorithmic complexity vulnerability in the inline link parser that allows unauthenticated attackers to exhaust CPU by submitting long runs of unmatched '[' characters. Attackers can send 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.

Affected products

lepture mistune: before 3.3.0 — fixed in 3.3.0

How to fix

Upgrade to a fixed version: lepture mistune 3.3.0. Check the vendor advisory for mitigations.

References

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