MEDIUM

CVE-2026-21871

CVSS v3

6.1

MEDIUM

EPSS Score

0.3 %

exploit probability, as of 2026-10-19

CISA KEV

known exploited

Exploitation

—

SSVC status

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Affected and fixed versions

Packages from OSV.dev and products from the vendors' CSAF advisories.

version not verifiedVersions not verified: read as OSV.dev and the vendors publish them, not checked against each vendor's release list.

Packages

niceguiPyPIfrom 2.13.0 · fixed in 3.5.0

Full record on NVD

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.

Technical details

Published: 2026-01-08

Frequently asked questions

What is CVE-2026-21871?

Is CVE-2026-21871 actively exploited?

Active exploitation of CVE-2026-21871 has not been confirmed. Its EPSS score was 0.3% on 2026-10-19, the estimated probability of exploitation in the next 30 days.

What is the CVSS score for CVE-2026-21871?

CVE-2026-21871 has a CVSS v3 base score of 6.1 (MEDIUM severity).

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