CVE-2026-27156 NiceGUI has XSS via Code Injection
Attackers can inject arbitrary JavaScript via user-controlled method names in NiceGUI APIs, leading to XSS in victim browsers.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- A user has to click or open something
- Fix
- Available
What is CVE-2026-27156?
CVE-2026-27156 is a medium-severity cross-site scripting vulnerability in zauberzeug nicegui, published on 24 Feb 2026. An attacker can exploit it over the internet without logging in, and only if a user opens a file or follows a link.
Official description
NiceGUI is a Python-based UI framework. Prior to version 3.8.0, several NiceGUI APIs that execute methods on client-side elements (`Element.run_method()`, `AgGrid.run_grid_method()`, `EChart.run_chart_method()`, and others) use an `eval()` fallback in the JavaScript-side `runMethod()` function. When user-controlled input is passed as the method name, an attacker can inject arbitrary JavaScript that executes in the victim's browser. Additionally, `Element.run_method()` and `Element.get_computed_prop()` used string interpolation instead of `json.dumps()` for the method/property name, allowing quote injection to break out of the intended string context. Version 3.8.0 contains a fix.
Weakness: CWE-79
Which versions are affected by CVE-2026-27156?
3 open source packages ship an affected version, including nicegui. It affects 1 product.
| Package | Affected | Fixed in |
|---|---|---|
nicegui PyPI | All versions | 3.8.0 |
nicegui PyPI | All versions | 3.8.0 |
nicegui PyPI | All versions | 3.8.0 |
Products include Zauberzeug Nicegui.
How do I fix CVE-2026-27156?
Upgrade nicegui to 3.8.0 or later.
Escape output for the context it lands in and set a strict Content Security Policy. Upgrading the affected component is the real fix. More about Cross-site scripting.
Is CVE-2026-27156 being exploited?
There is no known exploitation of CVE-2026-27156 in the wild and no public exploit code.
Other vulnerabilities in zauberzeug nicegui
- CVE-2026-25732 NiceGUI's Path Traversal via Unsanitized FileUpload.name Enables Arbitrary File Write
- CVE-2025-66645 NiceGUI Path Traversal Vulnerability in app.add_media_files() Allows Arbitrary File Reading
- CVE-2026-21873 Zero-click XSS in all NiceGUI apps which uses `ui.sub_pages`
- CVE-2026-33332 NiceGUI's unvalidated chunk size parameter in media routes can cause memory exhaustion
- CVE-2026-25516 NiceGUI's XSS vulnerability in ui.markdown() allows arbitrary JavaScript execution through unsanitized HTML content
Sources
Also known as GHSA-78qv-3mpx-9cqq, PYSEC-2026-2232.