Vulnerability · Published Jul 8, 2026 · Assigned by GitHub_M
CVE-2026-59923Mistune: XSS via percent-encoded javascript URI bypass in safe_url()
Medium 6.1
In plain English
A medium-severity cross-site scripting in mistune from lepture. Proof-of-concept exploit code is public. The chance it is exploited in the next 30 days is estimated at 0.3% (higher than 29% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.
Severity (CVSS 3.1)6.1Medium
Exploit odds (30 days)0.3%top 71.4% of all CVEs
Exploited in the wildNo reportsCISA SSVC: poc
Attack toolingNoneno public tooling known
Official description
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.
Affected packages & fixed versions
| Ecosystem | Package | Fixed in | Advisory |
|---|---|---|---|
| Debian:12 | mistune | no fix listed | DEBIAN-CVE-2026-59923 |
| Debian:13 | mistune | no fix listed | DEBIAN-CVE-2026-59923 |
| Debian:14 | mistune | no fix listed | DEBIAN-CVE-2026-59923 |
| PyPI | mistune | 3.3.0 | GHSA-8c25-4j27-2rv3 |
| PyPI | mistune | 3.3.0 | PYSEC-2026-2211 |
| Ubuntu:22.04:LTS | mistune | no fix listed | UBUNTU-CVE-2026-59923 |
| Ubuntu:24.04:LTS | mistune | no fix listed | UBUNTU-CVE-2026-59923 |
| Ubuntu:25.10 | mistune | no fix listed | UBUNTU-CVE-2026-59923 |
| Ubuntu:26.04:LTS | mistune | no fix listed | UBUNTU-CVE-2026-59923 |
| Ubuntu:26.10 | mistune | no fix listed | UBUNTU-CVE-2026-59923 |
Affected products (as reported)
Weakness: CWE-79 · Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N
References
- https://github.com/lepture/mistune/security/advisories/GHSA-8c25-4j27-2rv3 x_refsource_CONFIRM
- https://github.com/lepture/mistune/commit/c7101fcbb6e8790e8e39157c5ca2238fc6dd6cbc x_refsource_MISC
- https://github.com/lepture/mistune/releases/tag/v3.3.0 x_refsource_MISC