How severe is CVE-2026-21873?

CVE-2026-21873 has a CVSS 3.x base score of 7.2, rated high severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is low, integrity low, and availability none.

Is CVE-2026-21873 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 0% (14th percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2026-21873?

CVE-2026-21873 affects Zauberzeug Nicegui. See the affected-products list for the exact vulnerable versions.

How do I fix CVE-2026-21873?

Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its high severity, prioritise patching exposed systems.

Does CVE-2026-21873 have an EU (EUVD) identifier?

Yes. CVE-2026-21873 is tracked in the ENISA EU Vulnerability Database (EUVD) as EUVD-2026-1475.

When was CVE-2026-21873 published?

CVE-2026-21873 was published on 2026-01-08 and last updated on 2026-06-17.

CVE-2026-21873

CVE-2026-21873 is a high-severity vulnerability in Zauberzeug Nicegui with a CVSS 3.x base score of 7.2. It is not currently listed as actively exploited by CISA, and its EPSS exploit-prediction score is low. The underlying weakness is classified as CWE-79.

Key facts

Severity: High (CVSS 3.x base score 7.2)
EPSS exploit prediction: 0% (14th percentile)
Actively exploited: Not listed in CISA KEV
EU (EUVD) id: EUVD-2026-1475
Weakness: CWE-79
Affected product: Zauberzeug Nicegui
Published: 2026-01-08
Last modified: 2026-06-17

Description

NiceGUI is a Python-based UI framework. From versions 2.22.0 to 3.4.1, an unsafe implementation in the pushstate event listener used by ui.sub_pages allows an attacker to manipulate the fragment identifier of the URL, which they can do despite being cross-site, using an iframe. This issue has been patched in version 3.5.0.

Frequently asked questions

What is CVE-2026-21873?: NiceGUI is a Python-based UI framework. From versions 2.22.0 to 3.4.1, an unsafe implementation in the pushstate event listener used by ui.sub_pages allows an attacker to manipulate the fragment identifier of the URL, which they can do despite being cross-site, using an iframe. This issue has been patched in version 3.5.0.
How severe is CVE-2026-21873?: CVE-2026-21873 has a CVSS 3.x base score of 7.2, rated high severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is low, integrity low, and availability none.
Is CVE-2026-21873 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 0% (14th percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2026-21873?: CVE-2026-21873 affects Zauberzeug Nicegui. See the affected-products list for the exact vulnerable versions.
How do I fix CVE-2026-21873?: Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its high severity, prioritise patching exposed systems.
Does CVE-2026-21873 have an EU (EUVD) identifier?: Yes. CVE-2026-21873 is tracked in the ENISA EU Vulnerability Database (EUVD) as EUVD-2026-1475.
When was CVE-2026-21873 published?: CVE-2026-21873 was published on 2026-01-08 and last updated on 2026-06-17.

References

Affected products (1)

cpe:2.3:a:zauberzeug:nicegui:*:*:*:*:*:*:*:*

More vulnerabilities in Zauberzeug Nicegui

CVE-2026-33332 — High (CVSS 7.5): NiceGUI is a Python-based UI framework. Prior to version 3.9.0, NiceGUI's app.add_media_file() and…
CVE-2026-25732 — High (CVSS 7.5): NiceGUI is a Python-based UI framework. Prior to 3.7.0, NiceGUI's FileUpload.name property exposes client-supplied…
CVE-2025-66645 — High (CVSS 7.5): NiceGUI is a Python-based UI framework. Versions 3.3.1 and below are vulnerable to directory traversal through the…
CVE-2026-27156 — Medium (CVSS 6.1): NiceGUI is a Python-based UI framework. Prior to version 3.8.0, several NiceGUI APIs that execute methods on…
CVE-2026-25516 — Medium (CVSS 6.1): NiceGUI is a Python-based UI framework. The ui.markdown() component uses the markdown2 library to convert markdown…
CVE-2026-21872 — Medium (CVSS 6.1): NiceGUI is a Python-based UI framework. From versions 2.22.0 to 3.4.1, an unsafe implementation in the click event…

All CVEs affecting Zauberzeug Nicegui →

Other CWE-79 (Cross-site Scripting (XSS)) vulnerabilities

CVE-2025-49410 — Critical (CVSS 10.0): Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting') vulnerability in Imran Emu TC…
CVE-2024-47875 — Critical (CVSS 10.0): DOMPurify is a DOM-only, super-fast, uber-tolerant XSS sanitizer for HTML, MathML and SVG. DOMpurify was vulnerable to…
CVE-2024-6886 — Critical (CVSS 10.0): Improper Neutralization of Input During Web Page Generation (XSS or 'Cross-site Scripting') vulnerability in Gitea…
CVE-2023-45144 — Critical (CVSS 10.0): com.xwiki.identity-oauth:identity-oauth-ui is a package to aid in building identity and service providers based on…
CVE-2023-45138 — Critical (CVSS 10.0): Change Request is an pplication allowing users to request changes on a wiki without publishing the changes directly.…
CVE-2022-4361 — Critical (CVSS 10.0): Keycloak, an open-source identity and access management solution, has a cross-site scripting (XSS) vulnerability in the…

Browse all CWE-79 (Cross-site Scripting (XSS)) vulnerabilities →