Security readout for executives and security teams
Plain-English summary
CVE-2026-21874 affects NiceGUI applications that use Redis-backed storage. An unauthenticated person can repeatedly open and close browser tabs, causing Redis connections to leak until Redis reaches its connection limit. The application may remain running, but storage-dependent features can degrade or break. The issue is patched in NiceGUI 3.5.0.
Executive priority
Treat as a moderate availability risk. It is unlikely to expose data based on current sources, but it can disrupt application functionality for affected deployments. Upgrade exposed NiceGUI applications using Redis-backed storage during the next planned remediation window, sooner for customer-facing services.
Technical view
NiceGUI versions 2.10.0 through 3.4.1 do not release Redis connections tied to tab storage. The weakness is CWE-772: missing release of resources after effective lifetime. The CVSS 3.1 score is 5.3, network exploitable, low complexity, no privileges or user interaction, with low availability impact and no confidentiality or integrity impact reported.
Likely exposure
Exposure is likely for internet- or network-accessible NiceGUI applications running versions >=2.10.0 and <3.5.0 with Redis-backed storage enabled. NiceGUI deployments not using Redis-backed storage are not identified as affected in the provided sources.
Exploitation context
The source bundle does not indicate known active exploitation, and KEV is false. Exploitation does not require authentication and can be performed through normal browser behavior repeated at scale, causing Redis connection exhaustion and degraded storage functionality.
Researcher notes
The public sources describe the vulnerable condition and patch but do not provide evidence of exploitation in the wild. Analysis should focus on Redis-backed storage lifecycle behavior before and after commit 6c52eb2c90c4b67387c025b29646b4bc1578eb83, without assuming impact beyond service degradation and broken storage functionality.
Mitigation direction
- Upgrade NiceGUI to version 3.5.0 or later.
- Prioritize applications using Redis-backed storage and exposed to untrusted users.
- Review the GitHub advisory and release notes for vendor-specific guidance.
- Monitor Redis connection usage until all affected deployments are upgraded.
Validation and detection
- Inventory NiceGUI application versions across production and staging.
- Identify which NiceGUI applications use Redis-backed storage.
- Confirm affected deployments are below version 3.5.0.
- Check Redis logs and metrics for connection-limit errors.
- After upgrading, verify Redis connections are released during tab close activity.
Public sources used
Generated from the cited source records. This long-tail analysis has not been individually reviewed by a named human.
Conservative CVE-to-ATT&CK context
These mappings and lookup hints may be relevant to the vulnerability behavior, CWE, affected product, or exposure path. Glexia-inferred context is not an official MITRE, ATT&CK, CWE, or CVE Program mapping.
ATT&CK lookup starting points
Use these exact CWE pages and searches to review the Glexia ATT&CK library from this CVE's weakness and description context.
CWE-772: Exact CWE lookup
Use the exact CWE identifier as the starting point before reviewing related ATT&CK behavior. Open the exact CWE lookup page first, then review the ATT&CK searches from that MITRE weakness context. This is a Glexia lookup hint, not an official ATT&CK mapping.
Open ATT&CK lookupCVE-2026-21874 mapping review
Open the CVE-to-ATT&CK bridge for reviewed, inferred, or future official mappings tied to this CVE.
Open ATT&CK lookup- Severity
- Medium
- CVSS
- 5.3 (3.1)
- Known Exploited
- No
- Published
Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L
CNA and ADP enrichment extracted from CVE v5
These fields come from the CVE record and ADP containers, not from Glexia's Take. They preserve time-varying source decisions such as CISA SSVC, KEV status, CVSS metrics, and provider references.
CVSS vector scores
1 official scoreWe collect every scored CVSS vector available in the official CNA and ADP containers. When more than one version is present, the table keeps the source vectors side by side instead of collapsing them into the highest score.
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L3.91.4Primary CVE scoreVulnerability scoring details
Base CVSS 3.1 score
5.3MediumVector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L
Source materials
- CVE List V5 sourceCVE List V5
- https://github.com/zauberzeug/nicegui/security/advisories/GHSA-mp55-g7pj-rvm2CVE reference · x_refsource_CONFIRM
- https://github.com/zauberzeug/nicegui/commit/6c52eb2c90c4b67387c025b29646b4bc1578eb83CVE reference · x_refsource_MISC
- https://github.com/zauberzeug/nicegui/releases/tag/v3.5.0CVE reference · x_refsource_MISC
Products and packages named in the record
CWE details
CWE links open Glexia weakness intelligence pages with official CWE context, developer remediation guidance, and related CVE mappings.
Missing Release of Resource after Effective Lifetime
Missing Release of Resource after Effective Lifetime represents a recurring weakness pattern that can create exploitable paths when design, validation, or implementation controls are missing.