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.
References
History

Sat, 19 Sep 2026 22:00:00 +0000

Type Values Removed Values Added
Title Blind SSRF in Nextcloud Circles via Remote-Instance Verification

Sat, 19 Sep 2026 02:15:00 +0000

Type Values Removed Values Added
Title Blind SSRF in Nextcloud Circles via Remote-Instance Verification

Fri, 18 Sep 2026 21:30:00 +0000

Type Values Removed Values Added
Metrics ssvc

{'options': {'Automatable': 'no', 'Exploitation': 'none', 'Technical Impact': 'partial'}, 'version': '2.0.3'}


Fri, 18 Sep 2026 11:15:00 +0000

Type Values Removed Values Added
First Time appeared Nextcloud
Nextcloud server
Vendors & Products Nextcloud
Nextcloud server

Fri, 18 Sep 2026 01:45:00 +0000

Type Values Removed Values Added
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.
Weaknesses CWE-918
References
Metrics cvssV3_0

{'score': 6.2, 'vector': 'CVSS:3.0/AV:L/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N'}


cve-icon MITRE

Status: PUBLISHED

Assigner: hackerone

Published: 2026-09-18T01:26:04.650Z

Updated: 2026-09-18T19:41:07.400Z

Reserved: 2026-08-20T15:00:00.606Z

Link: CVE-2026-77164

cve-icon Vulnrichment

Updated: 2026-09-18T19:41:04.281Z

cve-icon NVD

Status : Deferred

Published: 2026-09-18T02:17:07.510

Modified: 2026-09-18T20:17:22.273

Link: CVE-2026-77164

cve-icon Redhat

No data.