XSS via .py file containing script tag interpreted as HTML
Summary
A vulnerability exists in the file preview/browsing feature of the application, where files with a .py extension that contain JavaScript code wrapped in <script> tags may be interpreted and executed as HTML in certain modes. This leads to a stored XSS vulnerability.
Affected Versions
PoC
Create a .py file with arbitrary JavaScript content wrapped in <script> tags. For example:
<script>alert(document.cookie);</script>
When a victim views the file in browsing mode (e.g., a rendered preview), the JavaScript is executed in the browser context.
Attack vector
An attacker can place such a .py file in the system via remote channels, such as:
- Convincing a webmaster to download or upload the file;
- Tricking users into accessing a file link via public URLs.
Required permissions
- None, if public or visitor access is enabled.
- If the file is uploaded by a user with elevated permissions, potential privilege boundaries may be crossed.
User interaction
Yes. The user must manually click to switch to the browsing or preview mode to trigger the script. And seems only when using ISO-8859-1 encoding.
Scope
- Unchanged
(S:U) - The attack does not cross system or privilege boundaries in general.
- ⚠️ Controversial edge case: If sensitive preview files are accessible due to misconfiguration, scope could be considered Changed
(S:C).
Impact
- Confidentiality: User information including cookies, login state, and localStorage may be accessed. Some files that only can be viewed via this user will leak too.
- Integrity & Availability: Not directly impacted.
Recommendations
- Treat all previewed file types (including non-HTML like .py) as plain text unless explicitly sanitized.
- Disable rendering modes that can interpret user-uploaded content as HTML.
Timeline
| Date |
Event |
| 2025-06-17 |
Vulnerability reported |
| 2025-06-17 |
Comminuty Manager confirmed |
| 2025-06-17 |
Fixed |
Credits
References
XSS via
.pyfile containing script tag interpreted as HTMLSummary
A vulnerability exists in the file preview/browsing feature of the application, where files with a
.pyextension that contain JavaScript code wrapped in<script>tags may be interpreted and executed as HTML in certain modes. This leads to a stored XSS vulnerability.Affected Versions
PoC
Create a
.pyfile with arbitrary JavaScript content wrapped in<script>tags. For example:When a victim views the file in browsing mode (e.g., a rendered preview), the JavaScript is executed in the browser context.
Attack vector
An attacker can place such a
.pyfile in the system via remote channels, such as:Required permissions
User interaction
Yes. The user must manually click to switch to the browsing or preview mode to trigger the script. And seems only when using
ISO-8859-1encoding.Scope
(S:U)- The attack does not cross system or privilege boundaries in general.(S:C).Impact
Recommendations
Timeline
Credits
4.0.0-rc.4References