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GHSA-v8qj-hxv7-mgvv
No affected components available
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.
<img width="331" height="258" alt="image" src="https://github.com/user-attachments/assets/bce2b754-56d1-4da1-90a9-22bcb93269f2" />
3- Clicking on the file, and clicking click me should pop an alert
<img width="1103" height="485" alt="image" src="https://github.com/user-attachments/assets/18754486-799b-434e-a2fc-dd7c09956a29" />
Remediation
Since mermaid has DOMPurify as a built-in, it is recommended to use the strict mode instead of loose.
The vulnerability can be exploited over the network without needing physical access. It is easy for an attacker to exploit this vulnerability. An attacker needs basic access or low-level privileges. The attacker needs the user to perform some action, like clicking a link. The vulnerability can affect other systems as well, not just the initial system. There is a high impact on the confidentiality of the information. There is a high impact on the integrity of the data.
Exploitation activity has been observed. Apply available patches or mitigations urgently.
Probability that this vulnerability will be exploited in the wild within the next 30 days.
We did not find any exploit available. Neither in GitHub repositories nor in the Exploit-Database.
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