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When decoded, it points to the at the link-local IP address 169.254.169.254 . Accessing this specific path allows an attacker to extract temporary IAM security credentials directly from an EC2 instance, potentially leading to a full cloud account takeover. Anatomy of the Attack
Once the attacker obtains these credentials, they can configure their local AWS CLI with the stolen keys and gain the exact same permissions as the compromised EC2 instance. Remediation and Defense Strategies
The attacker inputs the URL-encoded metadata path into the vulnerable parameter: callback-url=http%3A%2F%2F169.254.169.254%2Flatest%2Fmeta-data%2Fiam%2Fsecurity-credentials%2F .
The most effective defense against metadata exfiltration is upgrading from IMDSv1 to IMDSv2. When decoded, it points to the at the
This effectively thwarts simple SSRF attacks because most SSRF vulnerabilities allow an attacker to control the URL, but not the headers of the HTTP request.
These credentials are temporary and rotated automatically by AWS (usually every hour), ensuring that if a credential is intercepted, it has a short lifespan.
This string is a URL-encoded exploit payload used to test for Server-Side Request Forgery (SSRF) vulnerabilities, specifically targeting AWS Instance Metadata "good review" Remediation and Defense Strategies The attacker inputs the
: This updated version requires a session-oriented "token-based" approach. An attacker cannot simply perform a GET request; they must first perform a PUT request to get a token, which most SSRF vulnerabilities cannot do. You can find migration guides on the AWS Documentation page.
In a standard SSRF attack, an attacker provides this URL to a vulnerable application feature—such as a "URL uploader" or a "webhook callback" field. Because the request originates from inside the server’s trusted network, the Metadata Service assumes the request is legitimate and returns the instance's private credentials to the attacker. This effectively grants the attacker the same permissions as the server itself, potentially leading to full cloud environment compromise. The Evolution of Defense: IMDSv1 vs. IMDSv2
This threat actor exploited an SSRF flaw in Adminer (CVE-2021-21311) to steal credentials from IMDS, demonstrating that this attack vector has been weaponized by advanced persistent threat groups for years. These credentials are temporary and rotated automatically by
The most effective defense against SSRF-based credential theft is migrating to . IMDSv2 requires a PUT request to first obtain a session token, which then must be included as a header in subsequent GET requests. This stops most SSRF attacks, which typically only support simple GET requests. Enforce IMDSv2 by setting http_tokens = "required" in your instance metadata options and http_put_response_hop_limit = 1 to prevent forwarding.
Block requests resolving to private, loopback, or link-local IP addresses (such as 127.0.0.1 , 10.0.0.0/8 , and 169.254.169.254 ). 3. Deploy Web Application Firewalls (WAF)