How to remediate – Apple Filing Protocol Server Detection

1. Introduction

Apple Filing Protocol Server Detection indicates an Apple file sharing service is listening on a network port. This allows attackers to enumerate information about the Mac OS X server and potentially exploit known vulnerabilities in AFP. Systems running older versions of macOS, or those with intentionally enabled legacy services, are most affected. A successful attack could compromise confidentiality, integrity, and availability of files shared via AFP.

2. Technical Explanation

The vulnerability occurs because the Apple Filing Protocol (AFP) service is active on a network port, responding to requests for server information. An attacker can send a ‘FPGetSrvrInfo’ request to gather details about the system. While not directly exploitable itself, this discovery enables further reconnaissance and potential exploitation of known AFP vulnerabilities. There is no CVE associated with simply detecting the service; however, numerous vulnerabilities have been found in AFP over time (e.g., CVE-2017-11864). An attacker could use this information to target specific systems with known exploits.

• Root cause: The Apple Filing Protocol service is enabled and listening on a network port, allowing remote enumeration of server details.
• Exploit mechanism: An attacker sends an FPGetSrvrInfo request to the AFP service to gather information about the system. This information can then be used to identify potential vulnerabilities for exploitation.
• Scope: macOS systems running versions that support AFP are affected, including older OS X releases and potentially newer versions with legacy services enabled.

3. Detection and Assessment

You can confirm if a system is vulnerable by checking for the listening service or scanning network ports.

• Quick checks: Use the following command to check for open ports associated with AFP (548): netstat -an | grep .548
• Scanning: Nessus vulnerability ID 2017425 can detect this issue. Other scanners may have similar signatures.
• Logs and evidence: System logs may show connections to port 548, indicating AFP activity. Check system logs for related events.

netstat -an | grep .548

4. Solution / Remediation Steps

Disable the Apple Filing Protocol service if it is not required.

4.1 Preparation

• Dependencies: Ensure no critical applications rely on AFP functionality. Change windows may be required for production systems and should be approved by IT management.

4.2 Implementation

1. Step 1: Open System Preferences, then Sharing.
2. Step 2: Uncheck the “File Sharing” box if it is enabled.
3. Step 3: If File Sharing is enabled, click the Options button and uncheck “Share files and folders using AFP”.

4.3 Config or Code Example

Before

File Sharing: Enabled, Share files and folders using AFP: Checked

After

File Sharing: Disabled or Share files and folders using AFP: Unchecked

4.4 Security Practices Relevant to This Vulnerability

Several security practices can help prevent this issue.

• Practice 1: Least privilege – only enable services that are absolutely necessary, reducing the attack surface.
• Practice 2: Safe defaults – disable unnecessary services by default during system configuration.

4.5 Automation (Optional)

No automation is provided for this vulnerability due to the GUI-based nature of the fix.

5. Verification / Validation

• Post-fix check: Run netstat -an | grep .548. The command should return no results if the service is disabled.
• Re-test: Re-run the initial detection method (netstat -an | grep .548) to verify that port 548 is no longer listening.
• Smoke test: Verify that any applications dependent on file sharing are still functioning as expected.
• Monitoring: Monitor system logs for unexpected connections to port 548, which could indicate the service has been re-enabled.

netstat -an | grep .548

6. Preventive Measures and Monitoring

Update security baselines and policies to reflect the disabling of unnecessary services.

• Baselines: Update your system security baseline or policy to include a requirement for disabling AFP if it is not needed.
• Pipelines: Implement checks in CI/CD pipelines to ensure that unnecessary services are disabled during deployment.
• Asset and patch process: Review asset inventory regularly to identify systems with potentially vulnerable configurations, such as enabled legacy services.

7. Risks, Side Effects, and Roll Back

Disabling AFP may impact applications or users relying on file sharing functionality.

• Risk or side effect 1: Disabling AFP could break compatibility with older systems that rely on the protocol.
• Risk or side effect 2: Users may experience issues accessing shared files if they are accustomed to using AFP.
• Roll back: Re-enable File Sharing in System Preferences and check “Share files and folders using AFP” if needed.

8. References and Resources

Links related to the Apple Filing Protocol vulnerability.

• Vendor advisory or bulletin: https://support.apple.com/en-gb/HT201369
• NVD or CVE entry: https://nvd.nist.gov/vuln/detail/CVE-2017-11864
• Product or platform documentation relevant to the fix: https://en.wikipedia.org/wiki/Apple_Filing_Protocol