Ech0 Server-Side Request Forgery (SSRF) Vulnerability

Ech0, a service developed by lin-snow, is susceptible to a Server-Side Request Forgery (SSRF) vulnerability. The vulnerability lies in the fetchPeerConnectInfo function (internal/service/connect/connect.go) where httpUtil.SendRequest is used instead of SendSafeRequest. This oversight allows authenticated users to craft connections to internal or external services, leading to unauthorized information disclosure. Specifically, attackers can target internal services, cloud metadata endpoints like AWS IMDSv1 (169.254.169.254), GCE metadata, and the Kubernetes API (kubernetes.default.svc.cluster.local). The affected version is any version of ech0 prior to commit 1.4.8-0.20260503040602-091d26d2d942. This vulnerability was reported on May 7, 2026.

Attack Chain

1. The attacker authenticates to the Ech0 service.
2. The attacker crafts a malicious POST request to /api/connects to add a new connection.
3. In the POST request, the connect_url field is set to a URL pointing to an internal resource, such as http://169.254.169.254/latest/meta-data/instance-id (AWS metadata service) or http://kubernetes.default.svc.cluster.local:443/api (Kubernetes API).
4. The Ech0 server receives the POST request and stores the malicious connect_url.
5. The attacker triggers a health check on the newly created connection via a request to /api/connects/health.
6. The fetchPeerConnectInfo function is called with the attacker-controlled URL.
7. httpUtil.SendRequest makes an HTTP request to the specified internal resource without proper validation.
8. The response from the internal resource is returned to the attacker, potentially revealing sensitive information.

Impact

Successful exploitation of this SSRF vulnerability allows an attacker to access sensitive internal resources that are normally protected. This includes cloud metadata, such as AWS EC2 instance IDs, IAM roles, and other configuration details. Access to the Kubernetes API could allow for further lateral movement and privilege escalation within the Kubernetes cluster. The number of potential victims is dependent on the deployment scale and network architecture of Ech0 instances, but all authenticated users could potentially trigger the vulnerability.

Recommendation

• Apply the patch or upgrade to a version of Ech0 that includes the fix for this vulnerability (>= 1.4.8-0.20260503040602-091d26d2d942).
• Deploy the Sigma rule Detect Ech0 SSRF via Connection to Metadata Endpoint to identify attempts to exploit this vulnerability by detecting connections to common cloud metadata endpoints.
• Monitor network connections for outbound traffic originating from the Ech0 server to internal IP addresses or domains, specifically 169.254.169.254 and kubernetes.default.svc.cluster.local, as listed in the IOCs table.