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CVE-2026-21871

NiceGUI is vulnerable to XSS via Unescaped URL in ui.navigate.history.push() / replace()

MEDIUM
6.1
CVSS Score
Published: January 8, 2026 at 09:49 AM UTC
Updated: June 17, 2026 at 10:19 AM UTC
1 product affected across 1 vendorNicegui

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Severity
MEDIUM6.1
Exploit prediction
EPSS 0.3%
SSVC
PoC

Description

NiceGUI is a Python-based UI framework. From versions 2.13.0 to 3.4.1, there is a XSS risk in NiceGUI when developers pass attacker-controlled strings into ui.navigate.history.push() or ui.navigate.history.replace(). These helpers are documented as History API wrappers for updating the browser URL without page reload. However, if the URL argument is embedded into generated JavaScript without proper escaping, a crafted payload can break out of the intended string context and execute arbitrary JavaScript in the victim’s browser. Applications that do not pass untrusted input into ui.navigate.history.push/replace are not affected. This issue has been patched in version 3.5.0.

Affected

Our own answer: ranges merged, affected separated from platform-only, with confidence and review flags.

Nicegui· Zauberzeug
95%
v < 3.5.02.13.0 ≤ v < 3.5.0
Affected range stops below 3.5.0, so it looks safe — our inference, not a vendor statement

Remediation

No guide yet

No remediation guidance has been written for this CVE yet. What the record does show:

Patch and advisory references

References (2)

x_refsource_CONFIRMExploitVendor Advisory
Source: cverecord
https://github.com/zauberzeug/nicegui/security/advisories/GHSA-7grm-h62g-5m97
x_refsource_MISCRelease Notes
Source: cverecord
https://github.com/zauberzeug/nicegui/releases/tag/v3.5.0

SSVC — Action Prioritization

SSVCPoCNot automatablePartial impact

SSVC signals action urgency (what to patch first), separate from CVSS which measures severity.

CVSS

6.1MEDIUMGitHub_M
Attack Vector
NETWORK
Complexity
LOW
Privileges
NONE
User Interaction
REQUIRED
Scope
CHANGED
Confidentiality
LOW
Integrity
LOW
Availability
NONE
Vector?

Quick Info

StatusANALYZED
CWE
CWE-79

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