CVE-2026-76098 Mistune has Denial of Service — RecursionError via Excessive Emphasis Markers in Markdown
Crafted Markdown with excessive emphasis markers causes a RecursionError, crashing the parsing process in the Mistune library.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-76098?
CVE-2026-76098 is a high-severity denial of service vulnerability in lepture mistune, published on 24 Aug 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Official description
Mistune is a Python Markdown parser with renderers and plugins. Versions 3.3.0 through 3.3.2 are vulnerable to DoS through deeply nested tokens. HTML rendering creates deeply nested emphasis tokens from consecutive asterisk characters, and recursive rendering in HTMLRenderer.render_token() can exceed Python's recursion limit and raise RecursionError, allowing crafted Markdown to crash a parsing process. This issue is fixed in version 3.3.3
Weakness: CWE-674
Which versions are affected by CVE-2026-76098?
3 open source packages ship an affected version, including mistune.
| Package | Affected | Fixed in |
|---|---|---|
mistune PyPI | From 3.3.0 | 3.3.3 |
mistune PyPI | From 3.3.0 | 3.3.3 |
mistune PyPI | From 3.3.0 | 3.3.3 |
How do I fix CVE-2026-76098?
Upgrade mistune to 3.3.3 or later.
Upgrade, then put limits on request size, rate and nesting depth so one client cannot exhaust the service. More about Denial of service.
Is CVE-2026-76098 being exploited?
It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-76098 exists.
Sources
Also known as AZL-97956, DEBIAN-CVE-2026-76098, ECHO-47d2-ddd1-74a0, GHSA-6m44-fpc8-c3rq, MINI-x355-jpjp-p4hj, PYSEC-2026-3863 and 1 more.