Attack Chain

1. Initial Access via SSRF Vulnerability: An attacker identifies and exploits a Server-Side Request Forgery (SSRF) vulnerability within a public-facing web application, which could be running on Nginx, Apache, IIS, or Traefik.
2. Internal Request Injection: The attacker crafts a malicious HTTP request, embedding an internal cloud instance metadata service (IMDS) endpoint (e.g., http://169.254.169.254/latest/meta-data/) within a user-controlled URL or query parameter.
3. Web Server Initiates Internal Connection: The vulnerable web application processes the malicious request and, due to the SSRF flaw, makes an outbound HTTP connection to the specified internal IMDS endpoint as if it were a legitimate internal service request.
4. Metadata Service Response: The cloud instance metadata service responds to the web server's request, providing sensitive information such as temporary IAM role credentials (e.g., meta-data/iam/security-credentials), API tokens (e.g., latest/api/token), or instance configuration details.
5. Credential Exfiltration: The web application receives the sensitive metadata or credentials and, depending on the SSRF exploit, leaks this information back to the attacker as part of the HTTP response or through other channels.
6. Cloud Resource Compromise: The attacker uses the stolen temporary credentials to authenticate to the cloud provider's APIs (e.g., AWS CLI, GCP SDK), gaining unauthorized access to cloud resources, potentially leading to data exfiltration, privilege escalation, or further attacks.

Impact

A successful SSRF attack against cloud instance metadata services can lead to significant compromise of cloud environments. Attackers can steal temporary credentials associated with the compromised workload, gaining unauthorized access to critical cloud resources, sensitive data, and the ability to manipulate cloud configurations. This can result in data breaches, resource hijacking, disruption of services, and the establishment of persistent access within the victim's cloud infrastructure. The breadth of potential impact depends on the permissions granted to the compromised instance's role or service account, which often include access to databases, object storage, and other core services.

Recommendation

• Deploy the Sigma rule "Web Server Cloud Metadata SSRF Request" to your SIEM to detect inbound HTTP requests containing cloud metadata endpoints.
• Block the C2 domains and IP addresses listed in the IOC table at the network perimeter (firewall/WAF) to prevent outbound connections to known metadata services from unauthorized sources.
• Implement strict outbound access controls and allowlisting at the network and application layer to restrict web applications from initiating connections to link-local addresses (e.g., 169.254.169.254) and other internal network ranges.
• Enforce the use of IMDSv2 (Instance Metadata Service Version 2) on AWS EC2 instances, and similar authenticated access mechanisms for other cloud providers, to require session tokens for metadata access.
• Regularly review and audit the permissions of cloud instance roles and managed identities, adhering to the principle of least privilege to minimize the impact of credential compromise.