Vulnerability · Published Sep 18, 2026 · Assigned by hackerone
CVE-2026-77164
Medium 6.2
In plain English
A medium-severity server-side request forgery in Server from Nextcloud. There are no confirmed reports of exploitation so far. The chance it is exploited in the next 30 days is estimated at 0.2% (higher than 9% of all known vulnerabilities).
Official description
Circles' remote-instance signature verification fetches the attacker-supplied keyId URL before trust in the remote instance is established, and explicitly allows local/private addresses for this request, bypassing Nextcloud's core SSRF protections. The public, unauthenticated endpoints POST /apps/circles/event/ and POST /apps/circles/incoming/ reach this code path, allowing any unauthenticated user to force the server to issue a GET request to an internal address. The response body of the internal request is never returned to the requester, so this is blind SSRF: an attacker can determine whether an internal service is reachable, but cannot read its response contents through this endpoint alone.
Affected products (as reported)
Weakness: CWE-918 · Vector: CVSS:3.0/AV:L/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N