Medium severity · published Jul 8, 2026
CVE-2026-59930
Mistune toc / TableOfContents directive: heading IDs use predictable `toc_N` numbering with no slugification, allowing collision with attacker-controlled `id="toc_N"` content
4.3
CVSS
0.2%
EPSS
No
On KEV
Description
Mistune is a Python Markdown parser with renderers and plugins. Prior to 3.3.0, the toc plugin and TableOfContents directive generate heading IDs as predictable toc_N values without slugifying the heading text, allowing attacker-controlled id="toc_N" content to collide with generated anchors and redirect same-page navigation, CSS selectors, or JavaScript handlers. This issue is fixed in version 3.3.0.
CVSS vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:L/A:N
Attack vector
Network
Complexity
Low
Privileges
None
User interaction
Required
Confidentiality
None
Integrity
Low
Availability
None
Scope
Unchanged
Exploitation
Is it being used?
Exploit prediction (EPSS)0.2% · higher than 9% 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-2026-59930
CVE.org
https://www.cve.org/CVERecord?id=CVE-2026-59930
Patch
https://github.com/lepture/mistune/commit/c4093c4742ed0d10d9332fb8edb455869b7b581b
Release Notes
https://github.com/lepture/mistune/releases/tag/v3.3.0
Exploit
https://github.com/lepture/mistune/security/advisories/GHSA-2hm2-hc3v-44h9
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