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

Source: https://junglewise.ai/threats/cve-2026-25516-nicegui-s-xss-vulnerability-in-ui-markdown-allows-arbitrary  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-02-06  
License: CC BY 4.0 with a link back

CVE-2026-25516 · Severity: low · CVSS 3.1 · Published 2026-02-06

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.

Technologies: [nicegui (PyPI)](https://junglewise.ai/threats/technologies/nicegui). Vendors: [PyPI](https://junglewise.ai/threats/vendors/pypi).

## Quick answers

**Is CVE-2026-25516 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-25516 being exploited in the wild.

**How severe is CVE-2026-25516?** Low severity, with a CVSS score of 3.1, published 6 February 2026.

**Which products and versions are affected?** nicegui (PyPI) ECOSYSTEM:introduced=0,fixed=3.7.0.

**Is there a fix for CVE-2026-25516?** Yes. nicegui (PyPI): upgrade to 3.7.0 or later. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

**Am I affected by CVE-2026-25516?** Check whether you run nicegui (PyPI) at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

## How to fix

- nicegui (PyPI): upgrade to 3.7.0 or later

  ```sh
  pip install "nicegui>=3.7.0"
  ```


## Affected products

- nicegui (PyPI) ECOSYSTEM:introduced=0,fixed=3.7.0

## Identifiers

- CVE-2026-25516
- GHSA-v82v-c5x8-w282
- PYSEC-2026-2231

## Related threats

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- [PYSEC-2026-1702 - NiceGUI apps which use `ui.sub_pages` vulnerable to zero-click XSS](https://junglewise.ai/threats/cve-2026-21873-nicegui-apps-which-use-ui-sub-pages-vulnerable-to-zero-click-xss)
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