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.
Metrics
Affected Vendors & Products
References
| Link | Providers |
|---|---|
| https://hackerone.com/reports/3303283 |
|
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
|
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
|
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
Updated: 2026-09-18T19:41:04.281Z
Status : Deferred
Published: 2026-09-18T02:17:07.510
Modified: 2026-09-18T20:17:22.273
Link: CVE-2026-77164
No data.