Security readout for executives and security teams
Plain-English summary
NiceGUI applications may expose users to browser-based script execution if the app passes attacker-controlled URL strings into specific navigation history helpers. This is not a flaw in every NiceGUI app; it depends on how developers use ui.navigate.history.push() or replace(). The vendor patched the issue in NiceGUI 3.5.0.
Executive priority
Treat as a targeted remediation item for teams using NiceGUI. Prioritize internet-facing applications or workflows where URLs can be influenced by users. Upgrade to 3.5.0 and review affected helper usage, but avoid emergency escalation unless exposure is confirmed.
Technical view
CVE-2026-21871 is a CWE-79 XSS issue in NiceGUI versions 2.13.0 through 3.4.1. URL arguments passed to ui.navigate.history.push() or ui.navigate.history.replace() could be embedded into generated JavaScript without proper escaping, allowing crafted input to break string context and execute JavaScript in the victim browser.
Likely exposure
Exposure is limited to NiceGUI applications running affected versions and passing untrusted or attacker-influenced strings into ui.navigate.history.push() or ui.navigate.history.replace(). Applications that do not pass untrusted input to these helpers are stated as not affected.
Exploitation context
The CVSS vector indicates network reachability, low attack complexity, no privileges required, and required user interaction. The provided sources do not report active exploitation, and the CVE is not listed as KEV in the supplied bundle.
Researcher notes
The key exposure condition is developer-controlled data flow into the history helper URL argument. Sources describe the vulnerable range and fixed version, but do not provide exploit-in-the-wild evidence. Assessment should focus on framework version, helper usage, and whether external input reaches those calls.
Mitigation direction
- Upgrade NiceGUI to version 3.5.0 or later.
- Review use of ui.navigate.history.push() and replace() for untrusted input.
- Avoid passing attacker-controlled strings into these helpers.
- Check the GitHub advisory and release notes for vendor guidance.
Validation and detection
- Inventory NiceGUI versions in deployed applications.
- Identify applications using NiceGUI versions 2.13.0 through 3.4.1.
- Search code for ui.navigate.history.push() and ui.navigate.history.replace().
- Confirm whether arguments can be influenced by users or external input.
- Verify upgraded deployments are running NiceGUI 3.5.0 or later.
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-79: User-session and phishing behavior lookup
Client-side and session-facing weaknesses should be reviewed alongside initial-access and user-execution behaviors. 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-2026-21871 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
- 6.1 (3.1)
- Known Exploited
- No
- Published
Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N
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:R/S:C/C:L/I:L/A:N2.82.7Primary CVE scoreVulnerability scoring details
Base CVSS 3.1 score
6.1MediumVector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N
Source materials
- CVE List V5 sourceCVE List V5
- https://github.com/zauberzeug/nicegui/security/advisories/GHSA-7grm-h62g-5m97CVE reference · x_refsource_CONFIRM
- 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.