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Permission increase on re-sharing via OCS API (NC-SA-2017-001)

5th February 2017

Risk level: Medium

CVSS v3 Base Score: 5.4 (AV:N/AC:L/PR:L/UI:R/S:C/C:L/I:L/A:N)

CWE: Permission Issues (CWE-275)

HackerOne report: 169680

Description

A permission related issue within the OCS sharing API allowed an authenticated adversary to reshare shared files with an increasing permission set. This may allow an attacker to edit files in a share despite having only a 'read' permission set.

Note that this only affects folders and files that the adversary has at least read-only permissions for.

Affected Software

  • Nextcloud Server < 10.0.2 (CVE-2017-0883)
  • Nextcloud Server < 9.0.55 (CVE-2017-0883)

Action Taken

The permissions are now properly checked on the OCS endpoint.

Acknowledgements

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.