Trusted servers exchange can be triggered by attacker

Vulnerability Description

Nextcloud Server is a Nextcloud package that handles data storage. A vulnerability in federated share exists in versions prior to 19.0.11, 20.0.10, and 21.0.2. An attacker can gain access to basic information about users of a server by accessing a public link that a legitimate server user added as a federated share. This happens because Nextcloud supports sharing registered users with other Nextcloud servers, which can be done automatically when selecting the "Add server automatically once a federated share was created successfully" setting. The vulnerability is patched in versions 19.0.11, 20.0.10, and 21.0.2 As a workaround, disable "Add server automatically once a federated share was created successfully" in the Nextcloud settings.

References

• https://github.com/nextcloud/security-advisories/security/advisories/GHSA-j875-vr2q-h6x6
• https://hackerone.com/reports/1167853
• https://security.gentoo.org/glsa/202208-17