The correct answer is A because GuardDuty can detect and alert on EC2 instance credential exfiltration events. These events indicate that the credentials obtained from the EC2 instance metadata service are being used from an IP address that is owned by a differentAWS account than the one that owns the instance1. GuardDuty can also provide details such as the source and destination IP addresses, the AWS account ID of the attacker, and the API calls made using the exfiltrated credentials2.

The other options are incorrect because they do not provide the information needed to determine if the credentials were used to access the company’s resources from an external account. Option B is incorrect because Audit Manager does not generate InstanceCredentialExfiltration events. Audit Manager is a service that helpsyou continuously audit your AWS usage to simplify how you assess risk and compliance with regulations and industry standards3. Option C is incorrect because CloudTrail logs do not show the account ID of the caller for GetSessionToken API calls to AWS STS. CloudTrail logs show the account ID of the identity whose credentials were used to call the API4. Option D is incorrect because CloudWatch logs do not show the GetSessionToken API calls to AWS STS by default. CloudWatch logs can show the API calls made by AWS Lambda functions, Amazon API Gateway, and other AWS services that integrate with CloudWatch5.