Vulnerability in Lepture Mistune
CVE-2026-115347
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.
Published · last modified .
CVSS v3 metric
CVSS v3 base score 7.5 (High). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H.
EPSS exploit prediction
No EPSS score from FIRST.org yet. New CVEs usually get one within a few days; no score means no signal yet, not low risk. How EPSS works.
Affected products
Weakness classification (CWE)
References
- github.com/lepture/mistune/security/advisories/GHSA-f32h-38gf-rg5r (vendor-advisory)
- www.vulncheck.com/advisories/mistune-before-3.3.0-quadratic-denial-of-service-v… (third-party-advisory)
Frequently asked questions
- What is CVE-2026-115347?
- CVE-2026-115347 is a high-severity vulnerability in Lepture Mistune, classified under Inefficient Algorithmic Complexity. CVSS score: 7.5/10. Published 2026-10-22.
- How severe is CVE-2026-115347?
- High severity. CVSS v3 base score is 7.5 out of 10.