# 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.

- **Severity:** Medium 6.1 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N`)
- **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:** Yes
- **Published:** 24 Feb 2026
- **Updated:** 26 Feb 2026
- **Also known as:** GHSA-78qv-3mpx-9cqq, PYSEC-2026-2232

## 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 (Improper Neutralization of Input During Web Page Generation)

## Which versions are affected by CVE-2026-27156?

3 open source packages ship an affected version, including nicegui. It affects 1 product.


| Package | Ecosystem | 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: Zauberzeug Nicegui.

## How do I fix CVE-2026-27156?

Upgrade nicegui to 3.8.0 or later.

## 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](https://insights.sbomify.com/CVE-2026-25732/): NiceGUI's Path Traversal via Unsanitized FileUpload.name Enables Arbitrary File Write (high 7.5)
- [CVE-2025-66645](https://insights.sbomify.com/CVE-2025-66645/): NiceGUI Path Traversal Vulnerability in app.add_media_files() Allows Arbitrary File Reading (high 7.5)
- [CVE-2026-21873](https://insights.sbomify.com/CVE-2026-21873/): Zero-click XSS in all NiceGUI apps which uses `ui.sub_pages` (high 7.2)
- [CVE-2026-33332](https://insights.sbomify.com/CVE-2026-33332/): NiceGUI's unvalidated chunk size parameter in media routes can cause memory exhaustion (medium 6.9)
- [CVE-2026-25516](https://insights.sbomify.com/CVE-2026-25516/): NiceGUI's XSS vulnerability in ui.markdown() allows arbitrary JavaScript execution through unsanitized HTML content (medium 6.1)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-27156 and fix it if it is affected.

What it is: 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.
Exploitation: There is no known exploitation of CVE-2026-27156 in the wild and no public exploit code.

Affected packages and fixed versions:
- nicegui (PyPI): affected all versions; fixed in 3.8.0
- nicegui (PyPI): affected all versions; fixed in 3.8.0
- nicegui (PyPI): affected all versions; fixed in 3.8.0

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-27156/ (Markdown: https://insights.sbomify.com/CVE-2026-27156/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-27156
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-27156
- OSV: https://osv.dev/vulnerability/CVE-2026-27156

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-27156/
Summaries are generated and may contain mistakes; the official description above is the record.