CVE-2026-44897: medium-severity vulnerability in lepture mistune
Mistune Heading ID Attribute Injection XSS
Published · Updated
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13Vexday Risk Score
No sign of exploitation. No public exploitation artifact known so far.
ssvc Trackcvss 6.1epss 0.2%
Mistune is a Python Markdown parser with renderers and plugins. Prior to 3.2.1, HTMLRenderer.heading() builds the opening <hN> tag by string-concatenating the id attribute value directly into the HTML — with no call to escape(), safe_entity(), or any other sanitisation function. A double-quote character " in the id value terminates the attribute, allowing an attacker to inject arbitrary additional attributes (event handlers, src=, href=, etc.) into the heading element. This vulnerability is fixed in 3.2.1.
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N
Affected products
lepture · mistuneRelated CVEs — lepture mistune
In the same product, most dangerous first.
CVE-2026-59928HIGHMistune block_parser: quadratic-time parsing on long lists of repeated reference-link definitionsEPSS 0.7%CVE-2026-59925HIGHinline_parser: quadratic-time parsing on long runs of `**x**` and `***x***` emphasis pairsEPSS 0.6%CVE-2026-59922HIGHMistune plugins/formatting: quadratic-time parsing on long runs of `~~x~~`, `==x==`, and `^^x^^` markers (strikethrough / mark / insert)EPSS 0.6%CVE-2026-121437HIGHMistune 3.3.0 before 3.3.4 Quadratic-Time DoS via _process_emphasis_delimitersEPSS 0.6%CVE-2026-33079HIGHMistune ReDoS in LINK_TITLE_RE allows denial of service with crafted Markdown titlesEPSS 0.6%CVE-2026-59927MEDIUMMistune directives/include: mutual `.. include::` recursion crashes the renderer with `RecursionError`, denial of service via two attacker-controlled markdown filesEPSS 0.5%