Medium 6.1Published May 26, 2026

CVE-2026-44897Mistune Heading ID Attribute Injection XSS

Updated under an hour ago (Oct 27, 2026, 8:40 PM ET)

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Every CVE for lepture mistune

Exploited in the last 30 days

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: 6.1 MEDIUM (v3.1, CNA)CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N
Weakness (CWE): CWE-79
Known exploited: Not in CISA's KEV catalog
EPSS (exploitation in the next 30 days): Not loaded for this CVE
Assigned by: GitHub_M
NVD analysis: Analyzed
Record last updated: Jun 1, 2026
First seen by InfoSec Signals: Oct 9, 2026

Affected products

Affected products

lepture mistune lepture:mistune (from the name)	before 3.2.1	CNA record
mistune_project mistune mistune_project:mistune	before 3.2.1	NVD

References

References

https://github.com/lepture/mistune/security/advisories/GHSA-v87v-83h2-53w7	x-refsource-confirm, exploit, vendor-advisory
https://github.com/lepture/mistune/releases/tag/v3.2.1	x-refsource-misc, product, release-notes

The CVE record on cve.org NVD's entry

The CVE record is authoritative. Products marked “from the name” were identified from the CNA's free-text names, not a CPE, and are matched less certainly. This product uses the NVD API but is not endorsed or certified by the NVD.