SSRF in Nextcloud Server
CVE-2026-77164
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.
Vulnerability class: SSRF (Server-Side Request Forgery)
Published · last modified .
CVSS v3 metric
CVSS v3 base score 6.2 (Medium). Vector: CVSS:3.0/AV:L/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N.
EPSS exploit prediction
EPSS: 0.002 (8.5th percentile), scored .
Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 9th percentile — 8.5% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.
EPSS over last 30 days · oldest: 0.002 · newest: 0.002 · change: 0.000
Affected products
Weakness classification (CWE)
References
Frequently asked questions
- What is CVE-2026-77164?
- CVE-2026-77164 is a medium-severity vulnerability in Nextcloud Server, classified under Server-Side Request Forgery (SSRF). CVSS score: 6.2/10. Published 2026-09-18.
- How severe is CVE-2026-77164?
- Medium severity. CVSS v3 base score is 6.2 out of 10.