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CVE-2026-44897

Mistune Heading ID Attribute Injection XSS

Published: May 26, 2026Updated: May 26, 2026 Sources: CVE List NVD
NVD MITRE
6.1CVSS
MEDIUM

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.

EPSS Score
N/A
CISA KEV
Not in KEV
Exploits
No Known Exploits
Remediation
No Fix Available

CVSS Vector Breakdown

AV:NAC:LPR:NUI:RS:CC:LI:LA:N
Exploitability
AV:NAttack Vector
Network
AC:LAttack Complexity
Low
PR:NPrivileges Required
None
UI:RUser Interaction
Required
Scope
S:CScope
Changed
Impact
C:LConfidentiality
Low
I:LIntegrity
Low
A:NAvailability
None

Weaknesses

CWE-79

Affected Products

mistune
lepture

Attack Graph

Products CVE Techniques Tactics

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Exploitability

No known exploits, KEV entries, or remediation guidance available for this vulnerability yet.

MITRE ATT&CK

2 techniques
Execution
Initial Access
View detailed technique mapping

References

https://github.com/lepture/mistune/security/advisories/GHSA-v87v-83h2-53w7
github.com
https://github.com/lepture/mistune/releases/tag/v3.2.1
github.com

Timeline

Published
May 26, 2026
Last Updated
May 26, 2026

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