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

Mistune ReDoS in LINK_TITLE_RE allows denial of service with crafted Markdown titles

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.

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CWE-1333

mistune 安全漏洞

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。

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