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.
Published: 2026-09-18
Score: 6.2 Medium
EPSS: n/a
KEV: No
Impact: n/a
Action: n/a
AI Analysis

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Remediation

No vendor fix or workaround currently provided.

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Tracking

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Advisories

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References
Link Providers
https://hackerone.com/reports/3303283 cve-icon cve-icon
History

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'}

Subscriptions

No data.

cve-icon MITRE

Status: PUBLISHED

Assigner: hackerone

Published:

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

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

Link: CVE-2026-77164

cve-icon Vulnrichment

No data.

cve-icon NVD

Status : Received

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

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

Link: CVE-2026-77164

cve-icon Redhat

No data.

cve-icon OpenCVE Enrichment

No data.

Weaknesses
  • CWE-918

    Server-Side Request Forgery (SSRF)