UBUNTU-CVE-2026-59929
Mistune, a Python Markdown parser, prior to version 3.3.0, contains a vulnerability in its safe_url filter that allows certain legacy or chained URL schemes to bypass filtering. This can lead to potentially unsafe URLs being rendered in href and src attributes, which may enable script execution in affected user agents. The issue is fixed in version 3.3.0.
AI Analysis
Technical Summary
The vulnerability in Mistune affects versions prior to 3.3.0 where the safe_url filter only blocks javascript:, vbscript:, file:, and data: schemes but fails to block other legacy or chained schemes such as feed:, view-source:, jar:, livescript:, mocha:, ms-its:, mk:, and res:. These schemes can reach rendered href and src attributes, potentially allowing script execution in user agents that process these URLs. The flaw is addressed by updating to Mistune version 3.3.0.
Potential Impact
This vulnerability can lead to the execution of scripts via crafted URLs using legacy or chained schemes in rendered Markdown content. This may result in limited confidentiality and integrity impacts due to script execution in affected user agents. There is no indication of availability impact. No known exploits in the wild have been reported.
Mitigation Recommendations
A fix is available in Mistune version 3.3.0. Users should upgrade to version 3.3.0 or later to remediate this vulnerability. No additional vendor advisory content is provided, so patch status beyond this is not confirmed. Check the vendor advisory for current remediation guidance.
UBUNTU-CVE-2026-59929
Description
Mistune, a Python Markdown parser, prior to version 3.3.0, contains a vulnerability in its safe_url filter that allows certain legacy or chained URL schemes to bypass filtering. This can lead to potentially unsafe URLs being rendered in href and src attributes, which may enable script execution in affected user agents. The issue is fixed in version 3.3.0.
CVSS v3.1
Score 6.1medium
Affected software
pkg:deb/ubuntu/[email protected]?arch=source&distro=bionicpkg:deb/ubuntu/[email protected]+really0.8.4-1?arch=source&distro=jammypkg:deb/ubuntu/[email protected]?arch=source&distro=questingpkg:deb/ubuntu/[email protected]?arch=source&distro=resoluteRun on your own infrastructure? Check whether these packages are installed with threat-finder — our free open-source scanner.
AI-Powered Analysis
Machine-generated threat intelligence
Technical Analysis
The vulnerability in Mistune affects versions prior to 3.3.0 where the safe_url filter only blocks javascript:, vbscript:, file:, and data: schemes but fails to block other legacy or chained schemes such as feed:, view-source:, jar:, livescript:, mocha:, ms-its:, mk:, and res:. These schemes can reach rendered href and src attributes, potentially allowing script execution in user agents that process these URLs. The flaw is addressed by updating to Mistune version 3.3.0.
Potential Impact
This vulnerability can lead to the execution of scripts via crafted URLs using legacy or chained schemes in rendered Markdown content. This may result in limited confidentiality and integrity impacts due to script execution in affected user agents. There is no indication of availability impact. No known exploits in the wild have been reported.
Mitigation Recommendations
A fix is available in Mistune version 3.3.0. Users should upgrade to version 3.3.0 or later to remediate this vulnerability. No additional vendor advisory content is provided, so patch status beyond this is not confirmed. Check the vendor advisory for current remediation guidance.
Technical Details
- Gcve Source
- db.gcve.eu
- Osv Id
- UBUNTU-CVE-2026-59929
- Osv Schema Version
- 1.7.0
- Aliases
- []
- Ecosystems
- ["Ubuntu:16.04:LTS","Ubuntu:18.04:LTS","Ubuntu:20.04:LTS","Ubuntu:22.04:LTS","Ubuntu:24.04:LTS","Ubuntu:25.10","Ubuntu:26.04:LTS"]
- Database Specific Severity
- null
- Cvss Version
- 3.1
Threat ID: 6a58b44f68715ace43d6b6e8
Added to database: 07/16/2026, 10:37:03 UTC
Last enriched: 07/16/2026, 11:29:55 UTC
Last updated: 07/31/2026, 19:24:49 UTC
Views: 5
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