In cloud environments, attackers often exploit overlooked resource policies to gain unauthorized access. This blog delves into how attackers use backdoor resource policies to infiltrate cloud environments by manipulating trust policies, bucket permissions, snapshots, and other critical assets.
Understanding the Threat
In many cloud environments, attackers exploit gaps in resource policies such as IAM roles, S3 bucket policies, RDS snapshots, and other configurations, creating a stealthy path to access sensitive data and execute unauthorized actions. They leverage misconfigurations to add unknown accounts, their accounts, to the policy, allowing them to assume roles and gain privileges.
What is a Policy and How Does It Look Like?
A policy in cloud environments, and specifically in AWS, is a document that defines permissions and access controls for resources. It dictates who (user/account) has access, what actions they can perform, and on which resources. Policies are typically written in JSON format and contain elements like Effect (Allow/Deny), Action (e.g., s3:GetObject), Resource (e.g., specific S3 bucket), and Principal (the account or user granted permissions).
In AWS, policies can be modified to grant access to other AWS accounts via the Principal field. This field specifies who is allowed access, and it can include an AWS account ID, IAM user, role, or an entire organization. By modifying a policy to add another account’s ARN (Amazon Resource Name), you effectively grant that account permissions defined in the Action and Resource fields.
For example, adding "AWS": "arn:aws:iam::123456789012:root" to a policy allows full access for that external account. Attackers exploit this mechanism to gain unauthorized access by adding their account ID into roles or bucket policies, effectively backdooring the resource.
The Mechanics of the Attack
1. IAM Role Trust Policy Manipulation - Privilege escalation
Attackers target IAM roles by modifying trust policies, inserting their accounts, and gaining unauthorized access. By doing so, they can assume privileged roles, bypassing traditional access controls. A role trust policy defines which entities (users, groups, or accounts) can assume an AWS IAM role. It controls who is allowed to access and use the role's permissions by specifying a Principal in the policy. This policy is different from the permissions policy of the role, which defines what the action the role can perform, it defines who can assume it and use its permissions.
Example Attack Flow:
Gain initial access through phishing or compromised credentials.
Use IAM privileges to list roles and trust policies.
Modify the trust policy to include an attacker-controlled account.
Assume the modified role and gain access to resources.
2. S3 Bucket Policy Exploitation - Exfiltration
Attackers can add unauthorized accounts to bucket policies, enabling them to read, write, or even delete data. This method is particularly dangerous for sensitive logs or backups.
Example Attack Flow:
Discover misconfigured bucket policies allowing public access.
Modify bucket policy to grant access to an attacker's AWS account.
Retrieve, alter, or delete the data.
3. Snapshots and Backup Misuse
Snapshots of RDS, EBS, or other resources are often left unsecured. Attackers can copy or share these snapshots, exposing sensitive data or creating unauthorized clones.
Example Attack Flow:
List available snapshots using compromised credentials.
Modify the Snapshot Attributes, adding permissions to their account
Share or copy snapshots to an attacker's account.
Restore or analyze snapshots offline.
Conclusion
Backdoor resource policies represent a stealthy and dangerous attack vector in cloud environments. Understanding, investigating, and mitigating such threats are essential for maintaining a secure cloud infrastructure. By adopting robust monitoring, least privilege access, and proactive investigations, you can significantly reduce your exposure to these types of attacks.
Hands-On Attack Demonstration
Identifying Vulnerable Policies
Using AWS CLI or Boto3 (Python SDK), attackers can enumerate IAM roles, policies, and their trust relationships.
For example:
Assume the attacker can list the permissions policies of the role:
Full EC2 Access! - Targeting “aaa-test-role” and getting its policies:
Next, the attacker can modify the policy and update the assume role policy
We can see the policy was modified to trust the external Account ID. Every resource in this account can assume the role and have full EC2 Access to the target account.
Mitigation Strategies
To defend against potential abuse of backdoor resource policies in cloud environments, it's essential to implement the following mitigation strategies:
Audit Policies Regularly: Frequently review IAM roles, S3 bucket policies, and snapshot configurations to detect any unauthorized changes or additions. Use automation tools to streamline regular audits.
Enforce Least Privilege: Apply the principle of least privilege by restricting permissions to only what is necessary for users, roles, and services, reducing the risk of unauthorized access.
Enable Logging and Monitoring: Implement AWS CloudTrail and other monitoring tools to log and track changes to policies, trust relationships, and access configurations. This enables real-time alerts for suspicious activity.
Cyngular Security's CIRA platform
By applying these mitigation strategies and leveraging Cyngular Security's CIRA platform, organizations can effectively safeguard against backdoor resource policy exploitation, protecting sensitive roles, policies, and cloud resources from unauthorized access.
Cyngular Security's Cloud Investigation and Response Automation (CIRA) platform offers automated and efficient threat hunting, investigation, and response capabilities for cloud environments.
By integrating CIRA, your security team gains the ability to promptly address and neutralize potential threats, ensuring robust, proactive defense for your cloud assets. Embrace CIRA for a comprehensive security strategy that stays ahead of attackers.
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