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EUVD-2026-265149

fkie_cve-2026-21874

NiceGUI is a Python-based UI framework. From versions v2.10.0 to 3.4.1, an unauthenticated attacker can exhaust Redis connections by repeatedly opening and closing browser tabs on any NiceGUI application using Redis-backed storage. Connections are never released, leading to service degradation when Redis hits its connection limit. NiceGUI continues accepting new connections - errors are logged but the app stays up with broken storage functionality. This issue has been patched in version 3.5.0.

GHSA-mp55-g7pj-rvm2 — NiceGUI has Redis connection leak via tab storage causes service degradation

Affected: PyPI: nicegui

### Summary An unauthenticated attacker can exhaust Redis connections by repeatedly opening and closing browser tabs on any NiceGUI application using Redis-backed storage. Connections are never released, leading to service degradation when Redis hits its connection limit. **NiceGUI continues accepting new connections - errors are logged but the app stays up with broken storage functionality.**

### Details When a client disconnects, tab_id is cleared at https://github.com/zauberzeug/nicegui/blob/main/nicegui/client.py#L307 before delete() is called at https://github.com/zauberzeug/nicegui/blob/main/nicegui/client.py#L319. By then tab_id is None, so there's no way to find the RedisPersistentDict and call https://github.com/zauberzeug/nicegui/blob/main/nicegui/persistence/redis_persistent_dict.py#L92.

Each tab creates a RedisPersistentDict with a Redis client connection and a pubsub subscription. These are never closed, accumulating until Redis maxclients is reached.

### PoC #### Test server (test_connection_leak.py)

```python import os import logging from datetime import timedelta

import redis from nicegui import ui, app from nicegui.client import Client

logging.basicConfig(level=logging.WARNING, format="%(asctime)s %(levelname)s %(message)s") logging.getLogger("leak").setLevel(logging.INFO) log = logging.getLogger("leak")

_original_handle_disconnect = Client.handle_disconnect _original_delete = Client.delete

def _patched_handle_disconnect(self, socket_id: str) -> Non…

PYSEC-2026-1703 — NiceGUI has Redis connection leak via tab storage causes service degradation