VU#943094: ONLYOFFICE ownCloud integration plugin contains a Server-Side Request Forgery (SSRF) vulnerability

A Server-Side Request Forgery (SSRF) vulnerability exists in Ascensio System SIA's ONLYOFFICE ownCloud integration plugin (version 9.12). The plugin’s backend endpoint does not adequately validate the user‑supplied document server URL before initiating outbound connections. An authenticated administrator can exploit this flaw to coerce the ownCloud server into issuing arbitrary network requests to attacker‑controlled destinations.

The ownCloud ecosystem delivers a platform for enterprise file collaboration, providing capabilities for storing, syncing, and sharing data across devices. Ascensio System SIA's ONLYOFFICE provides a connector that integrates with ownCloud, enabling users to open and edit files directly within the cloud storage environment.

When configuring the ONLYOFFICE document server within ownCloud, the plugin accepts a document server parameter and attempts to verify the supplied URL by initiating a connection directly from the ownCloud server. As detailed in CVE-2026-84282, the application does not restrict or sanitize this parameter, allowing an authenticated administrator to provide arbitrary URLs, including internal network hosts or localhost addresses. By submitting crafted configuration requests to the /apps/onlyoffice/ajax/settings/address endpoint, an attacker can instruct the server to make outbound requests to internal systems that are otherwise inaccessible externally. Differences in returned error messages (such as connection failures versus SSL/TLS negotiation errors) enable the attacker to distinguish between open and closed TCP ports, facilitating internal network reconnaissance and port enumeration. The outbound requests originate from the ownCloud server, demonstrating server‑side request execution consistent with an SSRF vulnerability. This vulnerability could allow an attacker to abuse the ownCloud server infrastructure as a proxy to send malicious content to targeted systems.