CVE-2026-115347: Mistune before 3.3.0 Quadratic Denial of Service via parse_link_text

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 2026-10-26
Weakness: CWE-407

Description

Mistune before 3.3.0 contains an inefficient algorithmic complexity vulnerability in parse_link_text that allows remote attackers to cause denial of service through unbalanced square brackets. Attackers can submit markdown containing long runs of unmatched brackets to mistune.html(), triggering repeated forward scans that stall worker processes for minutes.

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

https://github.com/lepture/mistune/security/advisories/GHSA-f32h-38gf-rg5r
https://www.vulncheck.com/advisories/mistune-before-3.3.0-quadratic-denial-of-service-via-parse-link-text

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