CVE-2026-77164: CWE-918 Server-Side Request Forgery (SSRF) in Nextcloud Server
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.
AI Analysis
Technical Summary
The Circles app in Nextcloud Server versions >=31.0.0 <=32.0.0 performs remote-instance signature verification by fetching a keyId URL supplied by an attacker before establishing trust in the remote instance. This fetch explicitly allows requests to local or private IP addresses, bypassing Nextcloud's core SSRF protections. The vulnerable endpoints POST /apps/circles/event/ and POST /apps/circles/incoming/ are public and unauthenticated, enabling any unauthenticated user to trigger the SSRF. The server issues a GET request to the specified internal address, but the response body is not returned to the requester, making this a blind SSRF vulnerability.
Potential Impact
An unauthenticated attacker can use this SSRF vulnerability to probe internal network services by forcing the Nextcloud server to send GET requests to internal or private IP addresses. While the attacker cannot read the response content, they can determine the reachability of internal services. This could potentially aid in network reconnaissance and facilitate further attacks.
Mitigation Recommendations
Patch status is not yet confirmed — check the vendor advisory for current remediation guidance. Until an official fix is available, restrict access to the vulnerable endpoints and consider network-level controls to prevent unauthorized internal requests from the Nextcloud server.
CVE-2026-77164: CWE-918 Server-Side Request Forgery (SSRF) in Nextcloud Server
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.
CVSS v3.0
Score 6.2medium
Affected software
Nextcloud
Server
pkg:composer/nextcloud/serverRun on your own infrastructure? Check whether these packages are installed with threat-finder — our free open-source scanner.
Weaknesses
AI-Powered Analysis
Machine-generated threat intelligence
Technical Analysis
The Circles app in Nextcloud Server versions >=31.0.0 <=32.0.0 performs remote-instance signature verification by fetching a keyId URL supplied by an attacker before establishing trust in the remote instance. This fetch explicitly allows requests to local or private IP addresses, bypassing Nextcloud's core SSRF protections. The vulnerable endpoints POST /apps/circles/event/ and POST /apps/circles/incoming/ are public and unauthenticated, enabling any unauthenticated user to trigger the SSRF. The server issues a GET request to the specified internal address, but the response body is not returned to the requester, making this a blind SSRF vulnerability.
Potential Impact
An unauthenticated attacker can use this SSRF vulnerability to probe internal network services by forcing the Nextcloud server to send GET requests to internal or private IP addresses. While the attacker cannot read the response content, they can determine the reachability of internal services. This could potentially aid in network reconnaissance and facilitate further attacks.
Mitigation Recommendations
Patch status is not yet confirmed — check the vendor advisory for current remediation guidance. Until an official fix is available, restrict access to the vulnerable endpoints and consider network-level controls to prevent unauthorized internal requests from the Nextcloud server.
Technical Details
- Data Version
- 5.2
- Assigner Short Name
- hackerone
- Date Reserved
- 2026-08-20T15:00:00.606Z
- Cvss Version
- 3.0
- State
- PUBLISHED
Threat ID: 6aad953b55bf5e2cf577b8a5
Added to database: 09/18/2026, 19:47:07 UTC
Last enriched: 09/18/2026, 20:02:29 UTC
Last updated: 09/19/2026, 01:59:02 UTC
Views: 6
Community Reviews
0 reviewsCrowdsource mitigation strategies, share intel context, and vote on the most helpful responses. Sign in to add your voice and help keep defenders ahead.
Want to contribute mitigation steps or threat intel context? Sign in or create an account to join the community discussion.
Actions
Updates to AI analysis require Pro Console access. Upgrade inside Console → Billing.
External Links
Need more coverage?
Upgrade to Pro Console for AI refresh and higher limits.
For incident response and remediation, OffSeq services can help resolve threats faster.
Latest Threats
Check if your credentials are on the dark web
Instant breach scanning across billions of leaked records. Free tier available.