Check your EC2 security groups for inbound rules that allow unrestricted access (i.e. 0.0.0.0/0 or ::/0) to TCP port 445 and restrict access to only those IP addresses that require it in order to implement the principle of least privilege and reduce the possibility of a breach. Common Internet File System (CIFS) port 445 is used by client/server applications to provide shared access to files, printers and communications between network nodes directly over TCP (without NetBIOS) in Microsoft Windows Server 2003 and later. CIFS is based on the enhanced version of Server Message Block (SMB) protocol for internet/intranet file sharing, developed by Microsoft: https://goo.gl/VJyR8O.
This rule can help you with the following compliance standards:
- PCI
- APRA
- MAS
- NIST4
For further details on compliance standards supported by Conformity, see here.
This rule can help you work with the AWS Well-Architected Framework.
This rule resolution is part of the Conformity Security & Compliance tool for AWS.
Allowing unrestricted CIFS access can increase opportunities for malicious activity such as man-in-the-middle attacks (MITM), Denial of Service (DoS) attacks or the Windows Null Session Exploit.
Audit
To determine if your EC2 security groups allow unrestricted CIFS access, perform the following:
Remediation / Resolution
To update your security groups inbound/ingress configuration in order to restrict Common Internet File System (CIFS) access to specific entities (IP addresses, IP ranges and security groups), perform the following:
References
- AWS Documentation
- Amazon EC2 Security Groups for Linux Instances
- Security Groups for Your VPC
- Authorizing Inbound Traffic for Your Linux Instances
- AWS Command Line Interface (CLI) Documentation
- ec2
- describe-security-groups
- revoke-security-group-ingress
- authorize-security-group-ingress
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You are auditing:
Unrestricted CIFS Access
Risk level: Medium