CVE-2026-44898 Mistune TOC Anchor Injection XSS
An attacker can inject arbitrary HTML and scripts into the rendered table of contents by crafting malicious heading text, affecting applications using the Mistune library.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- A user has to click or open something
- Fix
- Available
What is CVE-2026-44898?
CVE-2026-44898 is a medium-severity cross-site scripting vulnerability in lepture mistune, published on 26 May 2026. An attacker can exploit it over the internet without logging in, and only if a user opens a file or follows a link.
Official description
Mistune is a Python Markdown parser with renderers and plugins. Prior to 3.2.1, render_toc_ul() builds a <ul> table-of-contents tree from a list of (level, id, text) tuples. Both the id value (used as href="#<id>") and the text value (used as the visible link label) are inserted into <a> tags via a plain Python format string — with no HTML escaping applied to either value. When heading IDs are derived from user-supplied heading text (the standard use-case for readable slug anchors), an attacker can craft a heading whose text breaks out of the href="#..." attribute context, injecting arbitrary HTML tags including <script> blocks directly into the rendered TOC. This vulnerability is fixed in 3.2.1.
Weakness: CWE-79
Which versions are affected by CVE-2026-44898?
3 open source packages ship an affected version, including mistune. It affects 1 product.
| Package | Affected | Fixed in |
|---|---|---|
mistune PyPI | All versions | 3.2.1 |
mistune PyPI | From 3.2.0 | 3.2.1 |
mistune PyPI | From 3.2.0 | 3.2.1 |
Linux distribution packages (1)
python-mistune SUSE:Linux Enterprise Module for Python 3 15 SP7 | All versions | 2.0.5-150400.11.8.1 |
Products include Mistune Project Mistune.
How do I fix CVE-2026-44898?
Upgrade mistune to 3.2.1 or later.
Escape output for the context it lands in and set a strict Content Security Policy. Upgrading the affected component is the real fix. More about Cross-site scripting.
Is CVE-2026-44898 being exploited?
It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-44898 exists.
Other vulnerabilities in lepture mistune
- CVE-2026-59922 Mistune plugins/formatting: quadratic-time parsing on long runs of `~~x~~`, `==x==`, and `^^x^^` markers (strikethrough / mark / insert)
- CVE-2026-59925 inline_parser: quadratic-time parsing on long runs of `**x**` and `***x***` emphasis pairs
- CVE-2026-59928 Mistune block_parser: quadratic-time parsing on long lists of repeated reference-link definitions
- CVE-2026-59923 Mistune: XSS via percent-encoded javascript URI bypass in safe_url()
- CVE-2026-59929 Mistune renderers/html.safe_url: HARMFUL_PROTOCOLS list misses legacy and chained schemes that historically chain to `javascript:` execution
Sources
Also known as AZL-88403, CLEANSTART-2026-PO47077, CLEANSTART-2026-QY40587, DEBIAN-CVE-2026-44898, GHSA-6269-cqxg-mhhv, PYSEC-2026-2208 and 2 more.