Vulnerability · Published Oct 22, 2026 · Assigned by VulnCheck
CVE-2026-115349Mistune 3.0.0 before 3.3.0 Denial of Service via Nested Bracket Parsing
High 7.5
In plain English
A high-severity regular-expression denial of service 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 0.3% (higher than 28% of all known vulnerabilities).
Severity (CVSS 3.1)7.5High
Exploit odds (30 days)0.3%top 72.0% of all CVEs
Exploited in the wildNo reportsCISA SSVC: none
Attack toolingNoneno public tooling known
Official description
Mistune from 3.0.0 before 3.3.0 contains an algorithmic complexity denial of service vulnerability in the parse_link_text function in src/mistune/helpers.py. Attackers can submit markdown with deeply nested square brackets triggering quadratic parsing time, exhausting server CPU with small crafted requests.
Affected packages & fixed versions
| Ecosystem | Package | Fixed in | Advisory |
|---|---|---|---|
| Debian:12 | mistune | no fix listed | DEBIAN-CVE-2026-115349 |
| Debian:13 | mistune | no fix listed | DEBIAN-CVE-2026-115349 |
| Debian:14 | mistune | no fix listed | DEBIAN-CVE-2026-115349 |
| Ubuntu:22.04:LTS | mistune | no fix listed | UBUNTU-CVE-2026-115349 |
| Ubuntu:24.04:LTS | mistune | no fix listed | UBUNTU-CVE-2026-115349 |
| Ubuntu:26.04:LTS | mistune | no fix listed | UBUNTU-CVE-2026-115349 |
| Ubuntu:26.10 | mistune | no fix listed | UBUNTU-CVE-2026-115349 |
Affected products (as reported)
Weakness: CWE-1333 · 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-3q64-rw38-243v) vendor-advisory
- VulnCheck Advisory: Mistune 3.0.0 before 3.3.0 Denial of Service via Nested Bracket Parsing third-party-advisory