CVE-2026-77164
MEDIUMDescription
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.
How to fix
No published remediation has been found for this vulnerability's affected products yet.
Mitigation guidance may be in the linked vendor advisories in the References section below.
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CVSS v3 Vector
Exploitability
Impact
CVSS:3.0/AV:L/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N
Exploit Intelligence
EPSS data unavailable for this CVE.
References
Related Vulnerabilities
Other CWE-918 (Server-Side Request Forgery (SSRF)) vulnerabilities, ordered by exploit likelihood. View all
| CVE | Severity | CVSS | EPSS | Exploited | Fix |
|---|---|---|---|---|---|
| CVE-2024-21893 | High | 8.2 | 100% | KEV + Ransom | - |
| CVE-2021-40438 | Critical | 9.0 | 100% | KEV + Ransom | Fix |
| CVE-2021-34473 | Critical | 9.1 | 100% | KEV + Ransom | Fix |
| CVE-2021-21985 | Critical | 9.8 | 100% | KEV + Ransom | Fix |
| CVE-2021-26855 | Critical | 9.1 | 100% | KEV + Ransom | Fix |
| CVE-2022-41040 | High | 8.8 | 100% | KEV + Ransom | Fix |
Common questions
How do I fix CVE-2026-77164?
No published fix for CVE-2026-77164 has been found yet. Check the linked vendor advisories for guidance as it becomes available.
How severe is CVE-2026-77164?
CVE-2026-77164 has a CVSS v3 base score of 6.2, rated medium. CVSS rates the technical impact if the vulnerability is exploited, not how likely that is, so weigh it alongside the exploit-prediction score when you decide what to patch first.
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Markdown
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This product uses NVD data but is not endorsed or certified by the NVD. EPSS scores courtesy of FIRST.org (https://www.first.org/epss). Source: CISA KEV Catalog. Data as of 2026-09-18.