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CVE-2026-21871

MEDIUMCVSS 6.1/10EPSS 0.24%

Last modified

CVE-2026-21871 is a medium-severity vulnerability rated 6.1/10 on the CVSS scale. 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(). EPSS estimates a 0.24% chance of exploitation in the next 30 days.

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.

Metrics

CVSS 3.1
6.1/10

CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N

EPSS Probability
0.24%

15.3th percentile

Probability of exploitation in the next 30 days. Learn more

Weakness Enumeration

Affected Software

VendorProductVersions
ZauberzeugNicegui>= 2.13.0, < 3.5.0

References

Timeline

Published
Last Modified
Status
Analyzed

Frequently Asked Questions

What is CVE-2026-21871?
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.
How severe is CVE-2026-21871?
CVE-2026-21871 has a CVSS score of 6.1/10 (MEDIUM severity). The EPSS model estimates a 0.24% probability of exploitation in the next 30 days.
How do I fix CVE-2026-21871?
Check the vendor references and advisories linked above for patched versions and mitigation guidance. You can also run a Strix scan to test if your systems are affected.

Are you affected by CVE-2026-21871?

Run a free Strix scan to check your systems for this vulnerability.

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Source: NVD / NIST