Medium severity · published Jul 8, 2026
CVE-2026-59923
Mistune: XSS via percent-encoded javascript URI bypass in safe_url()
6.1
CVSS
0.3%
EPSS
No
On KEV
Description
Mistune is a Python Markdown parser with renderers and plugins. Prior to 3.3.0, HTMLRenderer.safe_url() does not block percent-encoded javascript URIs, allowing attacker-supplied Markdown links or images to bypass URL protections and execute script in rendered HTML. This issue is fixed in version 3.3.0.
CVSS vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N
Attack vector
Network
Complexity
Low
Privileges
None
User interaction
Required
Confidentiality
Low
Integrity
Low
Availability
None
Scope
Changed
Exploitation
Is it being used?
Exploit prediction (EPSS)0.3% · higher than 28% of CVEs
Exploited in the wildNo evidence yet
CISA KEVNot listed
Ransomware campaign useNot known
Affected products
Which versions
MI
mistune · lepture
< 3.3.0 · source: vendor, NVD
References
NVD
https://nvd.nist.gov/vuln/detail/CVE-2026-59923
CVE.org
https://www.cve.org/CVERecord?id=CVE-2026-59923
Patch
https://github.com/lepture/mistune/commit/c7101fcbb6e8790e8e39157c5ca2238fc6dd6cbc
Release Notes
https://github.com/lepture/mistune/releases/tag/v3.3.0
Exploit
https://github.com/lepture/mistune/security/advisories/GHSA-8c25-4j27-2rv3
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