---
id: CVE-2025-53354
aliases:
  - GHSA-8c95-hpq2-w46f
  - PYSEC-2026-1699
title: NiceGUI has a Reflected XSS
summary: NiceGUI has a Reflected XSS
severity: medium
cvss: 6.1
cvssVector: 'CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N'
vendor: nicegui
product: nicegui
ecosystem: pip
affected:
  - nicegui < 3.0.0
patched:
  - nicegui 3.0.0
published: '2025-10-03'
updated: '2026-07-07'
source: OSV
sourceUrl: 'https://osv.dev/vulnerability/GHSA-8c95-hpq2-w46f'
references:
  - url: >-
      https://github.com/zauberzeug/nicegui/security/advisories/GHSA-8c95-hpq2-w46f
  - url: 'https://nvd.nist.gov/vuln/detail/CVE-2025-53354'
  - url: >-
      https://github.com/zauberzeug/nicegui/commit/4673dc35c94a0c7339e2164378b0977332e60775
  - url: 'https://github.com/zauberzeug/nicegui'
tags:
  - osv
  - pip
epss: 0.00204
epssPercentile: 0.09176
ingestedAt: '2026-07-08T18:25:47.432Z'
---

## Overview

### Summary

A Cross-Site Scripting (XSS) risk exists in NiceGUI when developers render unescaped user input into the DOM using `ui.html()`. Before version 3.0, NiceGUI does not enforce HTML or JavaScript sanitization, so applications that directly combine components like `ui.input()` with `ui.html()` without escaping may allow attackers to execute arbitrary JavaScript in the user’s browser. Same holds for `ui.chat_message` with HTML content.

Applications that directly reflect user input via `ui.html()` (or `ui.chat_message` in HTML mode) are affected. This may lead to client-side code execution (e.g., session hijacking or phishing). Applications that do not pass untrusted input into ui.html() are not affected.

### Details

NiceGUI allows developers to bind user input directly into the DOM using `ui.html()` or `ui.chat_message()`. However, the library does not enforce any HTML or JavaScript sanitization, which potentially creates a dangerous attack surface for developers unaware of this behavior.

The vulnerable code path appears when combining these:

```python
ui.input("XSS Input:", on_change=inject)
def inject(e):
    ui.html(f'{e.value}')
```

In this setup, any input provided by the user is rendered **verbatim** into the page’s DOM via innerHTML, enabling injection of script-based payloads.

### PoC (Proof of Concept)

1. Create a simple app:

   ```python
   from nicegui import ui

   @ui.page('/')
   def main():
       def inject(e):
           ui.html(f'{e.value}')  # vulnerable use

       ui.input("XSS Input:", on_change=inject)

   ui.run()
   ```

2. Run the app:

   ```bash
   python app.py
   ```

3. In the browser, input the following payload:

   ```html
   <img src=x onerror=alert('XSS')>
   ```

4. Observe the JavaScript alert popup:

   ```
   XSS
   ```

### Impact

* **Vulnerability type:** Reflected Cross-Site Scripting (XSS)
* **Attack vector:** User input rendered as raw HTML
* **Affected users:** Any NiceGUI-based application using `ui.html()` or `ui.chat_message()` with HTML content from user input

## Affected packages

- `nicegui < 3.0.0`

## Remediation

Upgrade to a patched release:

- `nicegui 3.0.0`