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CVE-2026-44899— Mistune Image Directive CSS Injection Vulnerability

Quick assessment

Affected
lepture mistune
Exploitation
No confirmed in-the-wild exploitation; assess based on exposure
Recommended action
Check the vendor advisory and references for a fixed version. If immediate upgrade is impossible, restrict exposure and increase monitoring.

mistune是Hsiaoming Yang个人开发者的一个快速而强大的 Python Markdown 解析器。 mistune 3.2.1之前版本存在跨站脚本漏洞，该漏洞源于Image指令插件使用仅匹配前缀的正则表达式验证width和height选项，验证后的值直接插入style属性而未进行转义，允许注入任意CSS代码。

CVSS 4.7 · Medium EPSS 0.27% · P18

Possible ATT&CK Techniques 1 AI

T1190 · Exploit Public-Facing Application

Affected Version Matrix 1

VendorProduct Version RangeStatus
lepture mistune < 3.2.1 affected
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I. Basic Information for CVE-2026-44899

Vulnerability Information
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Vulnerability Title
Mistune Image Directive CSS Injection Vulnerability
Source: CVE Program / CVE List V5
Vulnerability Description
Mistune is a Python Markdown parser with renderers and plugins. Prior to 3.2.1, the Image directive plugin validates the :width: and :height: options with a regex compiled as _num_re = re.compile(r"^\d+(?:\.\d*)?"). When the validated value is not a plain integer, render_block_image() inserts it directly into a style="width:...;" or style="height:...;" attribute. Because the value was accepted by the prefix-only regex, any CSS after the leading digits reaches the style= attribute verbatim and without escaping. This vulnerability is fixed in 3.2.1.
Source: CVE Program / CVE List V5
CVSS Information
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:N/A:N
Source: CVE Program / CVE List V5
Vulnerability Type
在Web页面生成时对输入的转义处理不恰当(跨站脚本)
Source: CVE Program / CVE List V5
Vulnerability Title
mistune 跨站脚本漏洞
Source: CNNVD (China National Vulnerability Database)
Vulnerability Description
mistune是Hsiaoming Yang个人开发者的一个快速而强大的 Python Markdown 解析器。 mistune 3.2.1之前版本存在跨站脚本漏洞，该漏洞源于Image指令插件使用仅匹配前缀的正则表达式验证width和height选项，验证后的值直接插入style属性而未进行转义，允许注入任意CSS代码。
Source: CNNVD (China National Vulnerability Database)
CVSS Information
N/A
Source: CNNVD (China National Vulnerability Database)
Vulnerability Type
N/A
Source: CNNVD (China National Vulnerability Database)

Affected Products

Vendor Product Affected Versions CPE Subscribe
lepture mistune < 3.2.1 -

II. Public POCs for CVE-2026-44899

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III. Intelligence Information for CVE-2026-44899

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Vendor Advisories for CVE-2026-44899 (1)

Vendor Pages for CVE-2026-44899 (1)

Same Patch Batch · lepture · 2026-05-26 · 5 CVEs total

CVE-2026-44898 6.1 MEDIUM Mistune TOC Anchor Injection XSS
CVE-2026-44897 6.1 MEDIUM Mistune Heading ID Attribute Injection XSS
CVE-2026-44708 6.1 MEDIUM Mistune Math Plugin XSS Escape Bypass
CVE-2026-44896 Mistune: XSS via unescaped figclass/figwidth in Figure directive

IV. Related Vulnerabilities

Same product: mistune
Same vendor: lepture
Same weakness: CWE-79

V. Comments for CVE-2026-44899

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