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Stored XSS in markdown file with Nextcloud Talk using Internet Explorer (NC-SA-2021-002)

18th November 2020

Risk level: Low

CVSS v3 Base Score: 3 (AV:N/AC:H/PR:L/UI:R/S:C/C:N/I:L/A:N)

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

HackerOne report: 1023787


A missing link validation in Nextcloud Server 20.0.1 allowed to execute a stored XSS attack on Internet Explorer users by saving a javascript url in a Markdown.

Affected Software

  • Nextcloud Server < 20.0.2 (CVE-2020-8294)
  • Nextcloud Server < 19.0.5 (CVE-2020-8294)
  • Nextcloud Server < 18.0.11 (CVE-2020-8294)

Action Taken

The error has been fixed.


It is recommended that the Nextcloud Server is upgraded to 20.0.2.


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

This advisory is licensed CC BY-SA 4.0.

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