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XSS in desktop client via invalid server address on login form (NC-SA-2020-027)

10th July 2020

Risk level: Low

CVSS v3 Base Score: 4.7 (AV:P/AC:L/PR:L/UI:R/S:C/C:L/I:L/A:L)

CWE: Cross-site Scripting (XSS) - Generic (CWE-79)

HackerOne report: 685552


A cross-site scripting error in Nextcloud Desktop client 2.6.4 allowed to present any html (including local links) when responding with invalid data on the login attempt.

Affected Software

  • Nextcloud Desktop < 2.6.5 (CVE-2020-8189)

Action Taken

The error has been fixed.


It is recommended that the Nextcloud Desktop client is upgraded to 2.6.5.


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

  • Juan Pablo Lopez Yacubian - Vulnerability discovery and disclosure.

This advisory is licensed CC BY-SA 4.0.

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