CVE-2026-59923: CWE-79: Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting') in lepture mistune
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.
AI Analysis
Technical Summary
CVE-2026-59923 describes a cross-site scripting (CWE-79) vulnerability in the Mistune Python Markdown parser. Specifically, before version 3.3.0, the HTMLRenderer.safe_url() function failed to block percent-encoded javascript URIs, enabling attackers to inject malicious scripts via Markdown links or images. This bypass of URL protections could lead to script execution in the rendered HTML output. The vulnerability is resolved in Mistune version 3.3.0.
Potential Impact
An attacker can craft Markdown content with specially encoded javascript URIs in links or images that bypass URL filtering, resulting in script execution in the rendered HTML context. This can lead to partial compromise of confidentiality and integrity (CVSS impact: Confidentiality Low, Integrity Low, Availability None). There is no indication of known exploits in the wild.
Mitigation Recommendations
Upgrade to Mistune version 3.3.0 or later, where the vulnerability is fixed. Patch status is confirmed by the version fix note. No other mitigations are specified or required.
CVE-2026-59923: CWE-79: Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting') in lepture mistune
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.
CVSS v3.1
Score 6.1medium
Affected software
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Weaknesses
AI-Powered Analysis
Machine-generated threat intelligence
Technical Analysis
CVE-2026-59923 describes a cross-site scripting (CWE-79) vulnerability in the Mistune Python Markdown parser. Specifically, before version 3.3.0, the HTMLRenderer.safe_url() function failed to block percent-encoded javascript URIs, enabling attackers to inject malicious scripts via Markdown links or images. This bypass of URL protections could lead to script execution in the rendered HTML output. The vulnerability is resolved in Mistune version 3.3.0.
Potential Impact
An attacker can craft Markdown content with specially encoded javascript URIs in links or images that bypass URL filtering, resulting in script execution in the rendered HTML context. This can lead to partial compromise of confidentiality and integrity (CVSS impact: Confidentiality Low, Integrity Low, Availability None). There is no indication of known exploits in the wild.
Mitigation Recommendations
Upgrade to Mistune version 3.3.0 or later, where the vulnerability is fixed. Patch status is confirmed by the version fix note. No other mitigations are specified or required.
Technical Details
- Data Version
- 5.2
- Assigner Short Name
- GitHub_M
- Date Reserved
- 2026-07-07T18:20:06.125Z
- Cvss Version
- 3.1
- State
- PUBLISHED
- Remediation Level
- null
Threat ID: 6a4e7ad5c9d9e3dbe36a7dee
Added to database: 07/08/2026, 16:29:09 UTC
Last enriched: 07/08/2026, 16:43:52 UTC
Last updated: 08/22/2026, 10:52:10 UTC
Views: 81
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