What is CVE-2026-59923?

CVE-2026-59923 is a medium-severity vulnerability in Lepture Mistune, classified under Cross-site Scripting. CVSS score: 6.1/10. Published 2026-07-08.

How severe is CVE-2026-59923?

Medium severity. CVSS v3 base score is 6.1 out of 10.

XSS in Lepture Mistune

CVE-2026-59923

Mistune is a Python Markdown parser with renderers and plugins. Prior to 3.3.0, HTMLRenderer.safe_url() does not block percent-encoded javascript URIs, allowing attacker-supplied Markdown links or images to bypass URL protections and execute script in rendered HTML. This issue is fixed in version 3.3.0.

Vulnerability class: XSS (Cross-Site Scripting)

Published 2026-07-08 · last modified 2026-07-09.

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 (26.3th percentile), scored 2026-10-09.

Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 26th percentile — 26.3% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.

EPSS over last 30 days · oldest: 0.003 · newest: 0.003 · change: 0.000

Affected products

Lepture Mistune — versions < 3.3.0
Mistune Project

Weakness classification (CWE)

CWE-79 — Cross-site Scripting

References

github.com/lepture/mistune/security/advisories/GHSA-8c25-4j27-2rv3 (Exploit, Vendor Advisory)
github.com/lepture/mistune/commit/c7101fcbb6e8790e8e39157c5ca2238fc6dd6cbc (Patch)
github.com/lepture/mistune/releases/tag/v3.3.0 (Release Notes)

Frequently asked questions

What is CVE-2026-59923?: CVE-2026-59923 is a medium-severity vulnerability in Lepture Mistune, classified under Cross-site Scripting. CVSS score: 6.1/10. Published 2026-07-08.
How severe is CVE-2026-59923?: Medium severity. CVSS v3 base score is 6.1 out of 10.