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Vulnerability · Published Jul 8, 2026 · Assigned by GitHub_M

CVE-2026-59929Mistune renderers/html.safe_url: HARMFUL_PROTOCOLS list misses legacy and chained schemes that historically chain to `javascript:` execution

Medium 6.1

In plain English

A medium-severity cross-site scripting in mistune from lepture. There are no confirmed reports of exploitation so far. The chance it is exploited in the next 30 days is estimated at 0.3% (higher than 28% 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 72.2% of all CVEs
Exploited in the wildNo reportsCISA SSVC: none
Attack toolingNoneno public tooling known

Official description

Mistune is a Python Markdown parser with renderers and plugins. Prior to 3.3.0, the safe_url filter in src/mistune/renderers/html.py blocks only javascript:, vbscript:, file:, and data: schemes, allowing legacy or chained schemes such as feed:, view-source:, jar:, livescript:, mocha:, ms-its:, mk:, and res: to reach rendered href and src attributes and potentially execute script in affected user agents. This issue is fixed in version 3.3.0.

Affected packages & fixed versions

EcosystemPackageFixed inAdvisory
Debian:12mistuneno fix listedDEBIAN-CVE-2026-59929
Debian:13mistuneno fix listedDEBIAN-CVE-2026-59929
Debian:14mistuneno fix listedDEBIAN-CVE-2026-59929
PyPImistune3.3.0GHSA-qfrw-5rxm-mhh2
PyPImistune3.3.0PYSEC-2026-2217
Ubuntu:22.04:LTSmistuneno fix listedUBUNTU-CVE-2026-59929
Ubuntu:24.04:LTSmistuneno fix listedUBUNTU-CVE-2026-59929
Ubuntu:25.10mistuneno fix listedUBUNTU-CVE-2026-59929
Ubuntu:26.04:LTSmistuneno fix listedUBUNTU-CVE-2026-59929
Ubuntu:26.10mistuneno fix listedUBUNTU-CVE-2026-59929

Affected products (as reported)

VendorProductVersions
lepture mistune < 3.3.0

Weakness: CWE-79, CWE-184 · Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N

References