Vulnerability · Published Oct 22, 2026 · Assigned by VulnCheck
CVE-2026-115352Mistune before 3.3.0 Quadratic-Time DoS via Unmatched Brackets in Inline Parser
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 38% of all known vulnerabilities).
Severity (CVSS 3.1)7.5High
Exploit odds (30 days)0.4%top 61.7% of all CVEs
Exploited in the wildNo reportsCISA SSVC: none
Attack toolingNoneno public tooling known
Official 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 packages & fixed versions
| Ecosystem | Package | Fixed in | Advisory |
|---|---|---|---|
| Debian:12 | mistune | no fix listed | DEBIAN-CVE-2026-115352 |
| Debian:13 | mistune | no fix listed | DEBIAN-CVE-2026-115352 |
| Debian:14 | mistune | no fix listed | DEBIAN-CVE-2026-115352 |
| Ubuntu:22.04:LTS | mistune | no fix listed | UBUNTU-CVE-2026-115352 |
| Ubuntu:24.04:LTS | mistune | no fix listed | UBUNTU-CVE-2026-115352 |
| Ubuntu:26.04:LTS | mistune | no fix listed | UBUNTU-CVE-2026-115352 |
| Ubuntu:26.10 | mistune | no fix listed | UBUNTU-CVE-2026-115352 |
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-xrpv-r66x-8p7j) vendor-advisory
- VulnCheck Advisory: Mistune before 3.3.0 Quadratic-Time DoS via Unmatched Brackets in Inline Parser third-party-advisory