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<h1>Security Advisory</h1>
<a href="/security/advisories/">Back to advisories</a>
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<h2>Permission increase on re-sharing via OCS API (NC-SA-2017-001)</h2>
<p>5th February 2017</p>
<p>Risk level: <strong>Medium</strong></p>
<p>CVSS v3 Base Score: 5.4 (<a href="https://www.first.org/cvss/calculator/3.0#CVSS:3.0/AV:N/AC:L/PR:L/UI:R/S:C/C:L/I:L/A:N">AV:N/AC:L/PR:L/UI:R/S:C/C:L/I:L/A:N</a>)</p>
<p>CWE: <a href="https://cwe.mitre.org/data/definitions/275.html">Permission Issues (CWE-275)</a></p>
<p>HackerOne report: <a href="https://hackerone.com/reports/169680">169680</a></p>
<h3>Description</h3>
<p>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.</p>
<h3>Affected Software</h3>
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<li>Nextcloud Server < <strong>10.0.2</strong> (CVE-2017-0883)</li>
<li>Nextcloud Server < <strong>9.0.55</strong> (CVE-2017-0883)</li>
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<h3>Action Taken</h3>
<p>The permissions are now properly checked on the OCS endpoint.</p>
<h3>Resolution</h3>
<p>It is recommended that all instances are upgraded to Nextcloud 9.0.55 or 10.0.2.</p>
<h3>Acknowledgements</h3>
<p>The Nextcloud team thanks the following people for their research and responsible disclosure of the above advisory:</p>
<ul>
<li><a href="https://secator.com/" target="_blank" rel="noreferrer">secator - Vulnerability discovery and disclosure.</a></li>
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<small style="color:grey">This advisory is licensed <a href="https://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA 4.0</a>.</small>
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