Vulnerability · Published Oct 22, 2026 · Assigned by VulnCheck
CVE-2026-115347Mistune before 3.3.0 Quadratic Denial of Service via parse_link_text
High 7.5
In plain English
A high-severity security flaw in mistune from lepture. There are no confirmed reports of exploitation so far. The chance it is exploited in the next 30 days is estimated at 0.4% (higher than 35% of all known vulnerabilities).
Severity (CVSS 3.1)7.5High
Exploit odds (30 days)0.4%top 64.5% of all CVEs
Exploited in the wildNo reportsCISA SSVC: none
Attack toolingNoneno public tooling known
Official 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 packages & fixed versions
| Ecosystem | Package | Fixed in | Advisory |
|---|---|---|---|
| Debian:12 | mistune | no fix listed | DEBIAN-CVE-2026-115347 |
| Debian:13 | mistune | no fix listed | DEBIAN-CVE-2026-115347 |
| Debian:14 | mistune | no fix listed | DEBIAN-CVE-2026-115347 |
| Ubuntu:22.04:LTS | mistune | no fix listed | UBUNTU-CVE-2026-115347 |
| Ubuntu:24.04:LTS | mistune | no fix listed | UBUNTU-CVE-2026-115347 |
| Ubuntu:26.04:LTS | mistune | no fix listed | UBUNTU-CVE-2026-115347 |
| Ubuntu:26.10 | mistune | no fix listed | UBUNTU-CVE-2026-115347 |
Affected products (as reported)
Weakness: CWE-407 · Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
References
- GitHub Security Advisory (GHSA-f32h-38gf-rg5r) vendor-advisory
- VulnCheck Advisory: Mistune before 3.3.0 Quadratic Denial of Service via parse_link_text third-party-advisory