---
id: CVE-2026-33079
title: >-
  In versions 3.0.0a1 through 3.2.0 of Mistune, there is a ReDoS (Regular
  Expression Denial of Service) vulnerability in `LINK_TITLE_RE` that allows an
  attacker who can supply Markdown for parsing to cause denial of service
summary: >-
  In versions 3.0.0a1 through 3.2.0 of Mistune, there is a ReDoS (Regular
  Expression Denial of Service) vulnerability in `LINK_TITLE_RE` that allows an
  attacker who can supply Markdown for parsing to cause denial of service. The
  regular ex…
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'
cwe:
  - CWE-1333
published: '2026-05-06'
updated: '2026-07-01'
source: NVD
sourceUrl: 'https://nvd.nist.gov/vuln/detail/CVE-2026-33079'
references:
  - url: >-
      https://github.com/lepture/mistune/blob/df23edd60b43b639d2e6760ef9dd3d618aa11c21/src/mistune/helpers.py#L20-L25
    label: security-advisories@github.com
  - url: 'https://github.com/lepture/mistune/security/advisories/GHSA-8mp2-v27r-99xp'
    label: security-advisories@github.com
  - url: 'https://access.redhat.com/security/cve/CVE-2026-33079'
    label: 0b0ca135-0b70-47e7-9f44-1890c2a1c46c
  - url: 'https://bugzilla.redhat.com/show_bug.cgi?id=2467298'
    label: 0b0ca135-0b70-47e7-9f44-1890c2a1c46c
  - url: 'https://github.com/lepture/mistune/security/advisories/GHSA-8mp2-v27r-99xp'
    label: 134c704f-9b21-4f2e-91b3-4a467353bcc0
  - url: >-
      https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-33079.json
    label: 0b0ca135-0b70-47e7-9f44-1890c2a1c46c
  - url: 'https://nvd.nist.gov/vuln/detail/CVE-2026-33079'
  - url: 'https://github.com/lepture/mistune'
tags:
  - nvd
  - osv
  - pip
epss: 0.00528
epssPercentile: 0.43702
ingestedAt: '2026-07-01T15:50:58.812Z'
aliases:
  - GHSA-8mp2-v27r-99xp
  - PYSEC-2026-2651
ecosystem: pip
vendor: mistune
product: mistune
affected:
  - 'mistune >= 3.0.0a1, < 3.2.1'
patched:
  - mistune 3.2.1
---

## Overview

In versions 3.0.0a1 through 3.2.0 of Mistune, there is a ReDoS (Regular Expression Denial of Service) vulnerability in `LINK_TITLE_RE` that allows an attacker who can supply Markdown for parsing to cause denial of service. The regular expression used for parsing link titles contains overlapping alternatives that can trigger catastrophic backtracking. In both the double-quoted and single-quoted branches, a backslash followed by punctuation can be matched either as an escaped punctuation sequence or as two ordinary characters, creating an ambiguous pattern inside a repeated group. If an attacker supplies Markdown containing repeated ! sequences with no closing quote, the regex engine explores an exponential number of backtracking paths. This is reachable through normal Markdown parsing of inline links and block link reference definitions. A small crafted input can therefore cause significant CPU consumption and make applications using Mistune unresponsive.

## Remediation

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

## Package advisory (CVE-2026-33079)

Affected packages:

- `mistune >= 3.0.0a1, < 3.2.1`

Patched in:

- `mistune 3.2.1`

Source: https://osv.dev/vulnerability/GHSA-8mp2-v27r-99xp