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CVE-2026-25516— NiceGUI's XSS vulnerability in ui.markdown() allows arbitrary JavaScript execution through unsanitized HTML content

Quick assessment

Affected
zauberzeug nicegui
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.

NiceGUI是NiceGUI开源的一个易于使用、基于 Python 的 UI 框架。 NiceGUI 3.7.0之前版本存在跨站脚本漏洞，该漏洞源于ui.markdown组件默认允许原始HTML通过，可能导致跨站脚本攻击。

CVSS 6.1 · Medium EPSS 0.32% · P24
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I. Basic Information for CVE-2026-25516

Vulnerability Information
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Vulnerability Title
NiceGUI's XSS vulnerability in ui.markdown() allows arbitrary JavaScript execution through unsanitized HTML content
Source: CVE Program / CVE List V5
Vulnerability Description
NiceGUI is a Python-based UI framework. The ui.markdown() component uses the markdown2 library to convert markdown content to HTML, which is then rendered via innerHTML. By default, markdown2 allows raw HTML to pass through unchanged. This means that if an application renders user-controlled content through ui.markdown(), an attacker can inject malicious HTML containing JavaScript event handlers. Unlike other NiceGUI components that render HTML (ui.html(), ui.chat_message(), ui.interactive_image()), the ui.markdown() component does not provide or require a sanitize parameter, leaving applications vulnerable to XSS attacks. This vulnerability is fixed in 3.7.0.
Source: CVE Program / CVE List V5
CVSS Information
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/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
NiceGUI 跨站脚本漏洞
Source: CNNVD (China National Vulnerability Database)
Vulnerability Description
NiceGUI是NiceGUI开源的一个易于使用、基于 Python 的 UI 框架。 NiceGUI 3.7.0之前版本存在跨站脚本漏洞，该漏洞源于ui.markdown组件默认允许原始HTML通过，可能导致跨站脚本攻击。
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
zauberzeug nicegui < 3.7.0 -

II. Public POCs for CVE-2026-25516

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III. Intelligence Information for CVE-2026-25516

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IV. Related Vulnerabilities

Same product: nicegui
Same vendor: zauberzeug
Same weakness: CWE-79

V. Comments for CVE-2026-25516

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