---
id: CVE-2026-115347
title: Mistune before 3.3.0 Quadratic Denial of Service via parse_link_text
summary: >-
  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 lon…
severity: high
cvss: 7.5
cvssVector: 'CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H'
cvssSource: cna
cwe:
  - CWE-407
  - CWE-606
vendor: lepture
product: mistune
affected:
  - mistune < 3.3.0
ssvc:
  exploitation: none
  automatable: 'yes'
  technicalImpact: partial
  timestamp: '2026-10-26T19:26:48.811448Z'
published: '2026-10-22'
updated: '2026-10-26'
sourceUpdated: '2026-10-26T19:38:30.510Z'
source: CVEORG
sourceUrl: 'https://www.cve.org/CVERecord?id=CVE-2026-115347'
references:
  - url: 'https://github.com/lepture/mistune/security/advisories/GHSA-f32h-38gf-rg5r'
    label: GitHub Security Advisory (GHSA-f32h-38gf-rg5r)
  - url: >-
      https://www.vulncheck.com/advisories/mistune-before-3.3.0-quadratic-denial-of-service-via-parse-link-text
    label: >-
      VulnCheck Advisory: Mistune before 3.3.0 Quadratic Denial of Service via
      parse_link_text
  - url: >-
      https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-115347.json
  - url: 'https://access.redhat.com/security/cve/CVE-2026-115347'
  - url: 'https://bugzilla.redhat.com/show_bug.cgi?id=2559327'
  - url: 'https://www.cve.org/CVERecord?id=CVE-2026-115347'
  - url: 'https://nvd.nist.gov/vuln/detail/CVE-2026-115347'
tags:
  - cve.org
  - csaf
  - vex
  - red-hat
epss: 0.0041
epssPercentile: 0.3506
ingestedAt: '2026-10-22T22:00:50.395Z'
---

## Overview

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

- `mistune < 3.3.0`

## Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.

## Vendor advisories

- **Red Hat VEX** · Important · affected: Red Hat OpenShift AI (RHOAI), Red Hat OpenShift Container Platform 4 · no fix planned: Red Hat OpenShift AI (RHOAI), Red Hat OpenShift Container Platform 4 · updated 2026-10-23 · [vex](https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-115347.json)