UBUNTU-CVE-2026-59923
Mistune is a Python Markdown parser vulnerable prior to version 3.3.0 due to its HTMLRenderer.safe_url() method not blocking percent-encoded javascript URIs. This allows attacker-supplied Markdown links or images to bypass URL protections and execute scripts in rendered HTML. 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 HTMLRenderer.safe_url() function fails to block percent-encoded javascript URIs. This flaw permits crafted Markdown content containing malicious links or images to bypass URL filtering protections, potentially leading to script execution in the rendered HTML output. The vulnerability is resolved in Mistune version 3.3.0.
Potential Impact
Successful exploitation can lead to limited confidentiality and integrity impacts by enabling script execution in the context of rendered Markdown content. This could allow attackers to execute malicious scripts in users' browsers when viewing affected Markdown, potentially leading to information disclosure or manipulation of rendered content. There is no impact on availability.
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 other mitigation steps are indicated.
UBUNTU-CVE-2026-59923
Description
Mistune is a Python Markdown parser vulnerable prior to version 3.3.0 due to its HTMLRenderer.safe_url() method not blocking percent-encoded javascript URIs. This allows attacker-supplied Markdown links or images to bypass URL protections and execute scripts in rendered HTML. 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 HTMLRenderer.safe_url() function fails to block percent-encoded javascript URIs. This flaw permits crafted Markdown content containing malicious links or images to bypass URL filtering protections, potentially leading to script execution in the rendered HTML output. The vulnerability is resolved in Mistune version 3.3.0.
Potential Impact
Successful exploitation can lead to limited confidentiality and integrity impacts by enabling script execution in the context of rendered Markdown content. This could allow attackers to execute malicious scripts in users' browsers when viewing affected Markdown, potentially leading to information disclosure or manipulation of rendered content. There is no impact on availability.
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 other mitigation steps are indicated.
Technical Details
- Gcve Source
- db.gcve.eu
- Osv Id
- UBUNTU-CVE-2026-59923
- 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: 6a58b45468715ace43d6b98d
Added to database: 07/16/2026, 10:37:08 UTC
Last enriched: 07/16/2026, 11:30:58 UTC
Last updated: 07/31/2026, 19:24:48 UTC
Views: 5
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