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Workflow rules only check the file extension for the mimetype instead of the content (NC-SA-2020-002)

4th December 2019

Risk level: Low

CVSS v3 Base Score: 5.5 (AV:N/AC:L/PR:L/UI:R/S:U/C:L/I:L/A:L)

CWE: Reliance on File Name or Extension of Externally-Supplied File (CWE-646)

HackerOne report: 697959


A bug in Nextcloud Server 17.0.1 causes the workflow rules to depend their behaviour on the file extension when checking file mimetypes.

Affected Software

  • Nextcloud Server < 17.0.2 (CVE-2019-15613)
  • Nextcloud Server < 16.0.7 (CVE-2019-15613)
  • Nextcloud Server < 15.0.14 (CVE-2019-15613)

Action Taken

The error has been fixed.


It is recommended that the Nextcloud Server is upgraded to 17.0.2.


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

  • Ralf Thesing - Vulnerability discovery and disclosure.

This advisory is licensed CC BY-SA 4.0.

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