Security Advisory

Back to advisories

Log pollution can potentially lead to local HTML injection (NC-SA-2016-002)

19th July 2016

Risk level: Low

CVSS v3 Base Score: 4.3 (AV:N/AC:L/PR:N/UI:R/S:U/C:L/I:N/A:N)

CWE: Cross-Site Scripting Using MIME Type Mismatch (CWE-209)

HackerOne report: 146278


The "download log" functionality in the admin screen is delivering the log in JSON format to the end-user. The file was delivered with an attachment disposition forcing the browser to download the document. However, Firefox running on Microsoft Windows would offer the user to open the data in the browser as HTML document. Thus any injected data in the log would be executed.While the document would only be executed locally (thus on another scope) we have decided to fix this to protect our users.

Affected Software

Action Taken

The file is now delivered with a content-type of "application/octet-stream".


It is recommended that all instances are upgraded to Nextcloud 9.0.52.


The Nextcloud team thanks the following people for their research and responsible disclosure of the above advisory:

  • Alejo Popovici - Vulnerability discovery and disclosure.

This advisory is licensed CC BY-SA 4.0.

You have javascript disabled. We tried to make sure the basics of our website work but some functionality will be missing.

This website is using cookies. By visiting you agree with our privacy policy. That's Fine