NiceGUI has Redis connection leak via tab storage causes service degradation

Exploitation

No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.

CVSS

5.3 · CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L

EPSS

• CVE-2026-21874: 0.55% estimated exploitation activity in the next 30 days; percentile 46.30 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.

As published by the source; long descriptions are shortened.

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, tabid 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 tabid is None, so there's no way to find the RedisPersistentDict and call https://github.com/zauberzeug/nicegui/blob/main/nicegui/persistence/redispersistentdict.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…

Published by the source

8 Jan 2026, 20:27 UTC

Last modified by the source

7 Jul 2026, 17:56 UTC

Source last checked

26 Oct 2026, 13:36 UTC

1. Revision 2 · amended · 26 Oct 2026

   Amended from ghsa record GHSA-mp55-g7pj-rvm2

2. Revision 1 · created · 24 Oct 2026

   Published from osv record GHSA-mp55-g7pj-rvm2

Preview the exact text before you copy it. Commands are read-only suggestions; review them before running anything.

# Patch Next advisory brief: CVE-2026-21874

Advisory: NiceGUI has Redis connection leak via tab storage causes service degradation
IDs: CVE-2026-21874, GHSA-mp55-g7pj-rvm2
Record: https://patchnext.com/advisories/cve-2026-21874 (revision 2, source checked 26 Oct 2026, 13:36 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Medium (CVSS 5.3)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: nicegui 3.5.0. A vendor fix does not mean a deployment is fixed.

## Affected components
- PyPI nicegui: affected >= 2.10.0, <= 3.4.1; fixed in 3.5.0

## Suggested inspection (read-only)
- `python -m pip show nicegui`: prints the installed version. Run with the environment that serves production active.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on nicegui.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://osv.dev/vulnerability/GHSA-mp55-g7pj-rvm2 (OSV record GHSA-mp55-g7pj-rvm2 lists affected ranges: PyPI nicegui >=2.10.0 <3.5.0 (fixed))
- Verified: https://github.com/advisories/GHSA-mp55-g7pj-rvm2 (GitHub-reviewed advisory GHSA-mp55-g7pj-rvm2 lists affected ranges: PyPI nicegui >=2.10.0 <=3.4.1)

Commands are suggestions: review each one before running it.