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CVE-2026-33079— Mistune ReDoS in LINK_TITLE_RE allows denial of service with crafted Markdown titles

Quick assessment

Affected
lepture mistune
Exploitation
No confirmed in-the-wild exploitation; assess based on exposure
Recommended action
Check the vendor advisory and references for a fixed version. If immediate upgrade is impossible, restrict exposure and increase monitoring.

mistune是Hsiaoming Yang个人开发者的一个快速而强大的 Python Markdown 解析器。 mistune 3.0.0a1版本至3.2.0版本存在安全漏洞，该漏洞源于LINK_TITLE_RE中正则表达式拒绝服务，可能导致攻击者提供Markdown解析时触发灾难性回溯，造成CPU过度消耗。

AI Predicted 7.5 Difficulty: Easy EPSS 0.52% · P42

Possible ATT&CK Techniques 1 AI

T1499 · Endpoint Denial of Service

Affected Version Matrix 1

VendorProduct Version RangeStatus
lepture mistune >=3.0.0a1, <= 3.2.0 affected
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I. Basic Information for CVE-2026-33079

Vulnerability Information
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Vulnerability Title
Mistune ReDoS in LINK_TITLE_RE allows denial of service with crafted Markdown titles
Source: CVE Program / CVE List V5
Vulnerability Description
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.
Source: CVE Program / CVE List V5
CVSS Information
CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N
Source: CVE Program / CVE List V5
Vulnerability Type
CWE-1333
Source: CVE Program / CVE List V5
Vulnerability Title
mistune 安全漏洞
Source: CNNVD (China National Vulnerability Database)
Vulnerability Description
mistune是Hsiaoming Yang个人开发者的一个快速而强大的 Python Markdown 解析器。 mistune 3.0.0a1版本至3.2.0版本存在安全漏洞，该漏洞源于LINK_TITLE_RE中正则表达式拒绝服务，可能导致攻击者提供Markdown解析时触发灾难性回溯，造成CPU过度消耗。
Source: CNNVD (China National Vulnerability Database)
CVSS Information
N/A
Source: CNNVD (China National Vulnerability Database)
Vulnerability Type
N/A
Source: CNNVD (China National Vulnerability Database)

Affected Products

Vendor Product Affected Versions CPE Subscribe
lepture mistune >=3.0.0a1, <= 3.2.0 -

II. Public POCs for CVE-2026-33079

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III. Intelligence Information for CVE-2026-33079

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Patches & Fixes for CVE-2026-33079 (1)

Vendor Advisories for CVE-2026-33079 (1)

IV. Related Vulnerabilities

Same product: mistune
Same vendor: lepture
Same weakness: CWE-1333

V. Comments for CVE-2026-33079

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