PT-2026-50483 · Pypi · Open-Webui

Published

2026-06-17

·

Updated

2026-06-17

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CVE-2026-54011

CVSS v3.1

8.7

High

VectorAV:N/AC:L/PR:L/UI:R/S:C/C:H/I:H/A:N

Summary

Open WebUI renders Mermaid blocks from Markdown files in the file preview panel and inserts the generated SVG into the DOM using innerHTML.
Because Mermaid is configured with securityLevel: 'loose', attacker-controlled Mermaid content can be rendered unsafely in this flow. A working payload was validated through the Markdown preview path, resulting in JavaScript execution in the victim’s browser under the application origin.
This is a confirmed stored XSS vulnerability reachable through normal product functionality.

Affected Version

  • main
  • Reproduced on v0.8.12

Affected Code

Mermaid is initialized in permissive mode:
https://github.com/open-webui/open-webui/blob/9bd84258d09eefe7bf975878fb0e31a5dadfe0f8/src/lib/utils/index.ts#L1698 The file preview path renders Mermaid output and injects the returned SVG into the DOM:
https://github.com/open-webui/open-webui/blob/9bd84258d09eefe7bf975878fb0e31a5dadfe0f8/src/lib/components/chat/FileNav/FilePreview.svelte#L133

Impact

A successful exploit allows JavaScript execution in the victim’s browser under the Open WebUI origin when a malicious Markdown file is opened in the preview panel.

PoC

A malicious .md file containing the follwowing contents can be used to trigger the bug:
```mermaid
flowchart LR
 A[click me]
 click A href "javascript:alert(document.domain)" "x"
```
Steps to reproduce: 1- Create a new chat 2- Enable Code Interpreter and browse and upload the file with .md extension. image 3- Clicking on the file, and clicking click me should pop an alert image

Remediation

Since mermaid has DOMPurify as a built-in, it is recommended to use the strict mode instead of loose.

Fix

XSS

Found an issue in the description? Have something to add? Feel free to write us 👾
dbugs@ptsecurity.com

Weakness Enumeration

CWE-79

Related Identifiers

CVE-2026-54011
GHSA-V8QJ-HXV7-MGVV

Affected Products

Open-Webui