CVE-2025-66469Public exploitNetwork attack vector

Reflected XSS via unescaped closing tags

Published Dec 8, 2025 · Updated Dec 9, 2025

Reflected XSS in NiceGUI 3.3.1 and earlier allows remote attackers to execute JavaScript via crafted style input. The ui.add_css function places content directly inside a style tag, while ui.add_scss and ui.add_sass embed content in script blocks without escaping less-than characters, so closing tags terminate the intended context. Exploitation requires an application to pass attacker-controlled input to one of these functions and a user to load the crafted page, exposing data and actions available to that browser session.

CVSS severity6.1
Medium
EPSS probability0.27%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Reflected XSS in NiceGUI 3.3.1 and earlier allows remote attackers to execute JavaScript via crafted style input. The ui.add_css function places content directly inside a style tag, while ui.add_scss and ui.add_sass embed content in script blocks without escaping less-than characters, so closing tags terminate the intended context. Exploitation requires an application to pass attacker-controlled input to one of these functions and a user to load the crafted page, exposing data and actions available to that browser session.

The record

CVE
CVE-2025-66469
Published
Dec 8, 2025
Updated
Dec 9, 2025
Vendor
Zauberzeug
Product
NiceGUI
Classifications
CWE-79, T1203
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Dec 8, 2025CVE publishedPublication date reported by the CVE source.
  2. Dec 9, 2025Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=< 3.4.0

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Zauberzeug · NiceGUIversion=< 3.4.0

Published CVSS scores

6.1GitHubCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

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No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitPublished

Weakness, pattern, technique

CWE-79Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')
T1203Exploitation for Client Execution

Public exploit references

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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