CVE-2026-44899: CWE-79: Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting') in lepture mistune
CVE-2026-44899 is a cross-site scripting (XSS) vulnerability in the lepture mistune Python Markdown parser prior to version 3.2.1. The issue arises from improper validation of the :width: and :height: options in the Image directive plugin, where a regex only partially validates numeric input, allowing additional CSS to be injected into style attributes without escaping. This vulnerability allows an attacker to inject arbitrary CSS into rendered HTML. The vulnerability is fixed in version 3.2.1. The CVSS score is 4.7, indicating a medium severity level.
AI Analysis
Technical Summary
Mistune versions before 3.2.1 contain a CWE-79 cross-site scripting vulnerability in the Image directive plugin. The plugin uses a regex to validate :width: and :height: options, but the regex only ensures the input starts with digits and allows trailing CSS code to be included unescaped in style attributes. This improper neutralization of input during web page generation can lead to injection of malicious CSS. The issue is resolved in version 3.2.1.
Potential Impact
An attacker can inject arbitrary CSS into the style attributes of images rendered by mistune, potentially affecting the appearance or behavior of web pages using vulnerable versions. The CVSS vector indicates the attack can be performed remotely without privileges but requires user interaction. The impact is limited to confidentiality with no integrity or availability impact reported.
Mitigation Recommendations
Upgrade mistune to version 3.2.1 or later where this vulnerability is fixed. No other official remediation or temporary fixes are documented. Patch status is not explicitly stated in vendor advisory content but the description confirms the fix is in 3.2.1.
CVE-2026-44899: CWE-79: Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting') in lepture mistune
Description
CVE-2026-44899 is a cross-site scripting (XSS) vulnerability in the lepture mistune Python Markdown parser prior to version 3.2.1. The issue arises from improper validation of the :width: and :height: options in the Image directive plugin, where a regex only partially validates numeric input, allowing additional CSS to be injected into style attributes without escaping. This vulnerability allows an attacker to inject arbitrary CSS into rendered HTML. The vulnerability is fixed in version 3.2.1. The CVSS score is 4.7, indicating a medium severity level.
CVSS v3.1
Score 4.7medium
Affected software
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Weaknesses
AI-Powered Analysis
Machine-generated threat intelligence
Technical Analysis
Mistune versions before 3.2.1 contain a CWE-79 cross-site scripting vulnerability in the Image directive plugin. The plugin uses a regex to validate :width: and :height: options, but the regex only ensures the input starts with digits and allows trailing CSS code to be included unescaped in style attributes. This improper neutralization of input during web page generation can lead to injection of malicious CSS. The issue is resolved in version 3.2.1.
Potential Impact
An attacker can inject arbitrary CSS into the style attributes of images rendered by mistune, potentially affecting the appearance or behavior of web pages using vulnerable versions. The CVSS vector indicates the attack can be performed remotely without privileges but requires user interaction. The impact is limited to confidentiality with no integrity or availability impact reported.
Mitigation Recommendations
Upgrade mistune to version 3.2.1 or later where this vulnerability is fixed. No other official remediation or temporary fixes are documented. Patch status is not explicitly stated in vendor advisory content but the description confirms the fix is in 3.2.1.
Technical Details
- Data Version
- 5.2
- Assigner Short Name
- GitHub_M
- Date Reserved
- 2026-05-07T21:50:33.546Z
- Cvss Version
- 3.1
- State
- PUBLISHED
- Remediation Level
- null
Threat ID: 6a16f9eae29bf47b50c0f5c8
Added to database: 05/27/2026, 14:04:26 UTC
Last enriched: 06/03/2026, 21:13:29 UTC
Last updated: 07/31/2026, 19:22:59 UTC
Views: 74
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