XSS in Lepture Mistune
CVE-2026-44897
Mistune is a Python Markdown parser with renderers and plugins. Prior to 3.2.1, HTMLRenderer.heading() builds the opening <hN> tag by string-concatenating the id attribute value directly into the HTML — with no call to escape(), safe_entity(), or any other sanitisation function. A double-quote character " in the id value terminates the attribute, allowing an attacker to inject arbitrary additional attributes (event handlers, src=, href=, etc.) into the heading element. This vulnerability is fixed in 3.2.1.
Vulnerability class: XSS (Cross-Site Scripting)
Published · last modified .
CVSS v3 metric
CVSS v3 base score 6.1 (Medium). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N.
EPSS exploit prediction
EPSS: 0.003 (18.2th percentile), scored .
Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 18th percentile — 18.2% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.
EPSS over last 30 days · oldest: 0.002 · newest: 0.003 · change: +0.000
Affected products
- Lepture Mistune — versions < 3.2.1
- Mistune Project
Weakness classification (CWE)
References
- github.com/lepture/mistune/releases/tag/v3.2.1 (Product, Release Notes)
- github.com/lepture/mistune/security/advisories/GHSA-v87v-83h2-53w7 (Exploit, Vendor Advisory)
Frequently asked questions
- What is CVE-2026-44897?
- CVE-2026-44897 is a medium-severity vulnerability in Lepture Mistune, classified under Cross-site Scripting. CVSS score: 6.1/10. Published 2026-05-26.
- How severe is CVE-2026-44897?
- Medium severity. CVSS v3 base score is 6.1 out of 10.