How to remediate – Identd Service Detection

1. Introduction

The Identd Service Detection vulnerability means a remote host is running an identification service, also known as ‘auth’. This service provides sensitive information to potential attackers about which accounts are running which services, helping them target valuable systems. A successful exploit could lead to reconnaissance and potentially compromise of the system. Confidentiality, integrity, and availability may be impacted if attackers gain access to sensitive information or control of affected systems.

2. Technical Explanation

The Identd service allows remote hosts to query which user account owns a particular process on the server. Attackers can use this information to map out the system and identify potential targets, such as root-owned services. The ‘ident’ protocol is unauthenticated and inherently insecure. If an attacker knows the username associated with a specific port, they may be able to gain further access or exploit vulnerabilities in those services.

• Root cause: The ident daemon is running and responding to queries without authentication.
• Exploit mechanism: An attacker connects to the server’s ident port (typically 113) and requests information about a specific username or service. This reveals sensitive account details. For example, an attacker could query for the user associated with SSH on port 22.
• Scope: Systems running any operating system that supports the ‘ident’ daemon, including Linux, Unix, and older versions of Windows.

3. Detection and Assessment

You can confirm if a system is vulnerable by checking if the identd service is running. A quick check involves using netstat or ss to see if port 113 is open. A thorough method includes examining process lists for the ‘identd’ daemon.

• Quick checks: Use the following command to check if port 113 is listening: netstat -tulnp | grep :113
• Scanning: Nessus vulnerability ID 24867 can detect running identd services. This is an example only.
• Logs and evidence: Check system logs for messages related to the ‘ident’ service or daemon startup. Log files may vary depending on the operating system.

netstat -tulnp | grep :113

4. Solution / Remediation Steps

To fix this issue, disable the identd service if it is not required. Only include steps that apply to this vulnerability.

4.1 Preparation

• Change window: Coordinate with system administrators for a planned maintenance window.

4.2 Implementation

1. Step 1: Stop the identd service using your operating system’s service management tool (e.g., systemctl stop identd on Linux).
2. Step 2: Disable the identd service from starting automatically at boot (e.g., systemctl disable identd on Linux).
3. Step 3: Verify that the service is stopped and disabled using systemctl status identd.

4.3 Config or Code Example

Before

# /etc/xinetd.d/ident (example)
service ident {
  disable = no
  ...
}

After

# /etc/xinetd.d/ident (example)
service ident {
  disable = yes
  ...
}

4.4 Security Practices Relevant to This Vulnerability

Several security practices can help prevent this issue. Least privilege reduces the impact if exploited, and safe defaults minimize unnecessary services running on a system.

• Practice 1: Least privilege – Run services with the minimum necessary privileges to limit potential damage from compromise.
• Practice 2: Safe defaults – Disable unnecessary services by default to reduce the attack surface.

4.5 Automation (Optional)

#!/bin/bash
# Check if identd is running
if systemctl is-active --quiet identd; then
  # Stop and disable the service
  systemctl stop identd
  systemctl disable identd
  echo "Identd service stopped and disabled."
else
  echo "Identd service not running."
fi

5. Verification / Validation

Confirm the fix by checking that port 113 is no longer listening and that the ‘identd’ service does not start automatically. Perform a simple smoke test to ensure other services are still functioning correctly.

• Post-fix check: Run netstat -tulnp | grep :113. The output should be empty, indicating port 113 is no longer listening.
• Re-test: Re-run the quick check from Section 3 to confirm that the service remains stopped and disabled.
• Monitoring: Monitor system logs for any errors related to the ‘ident’ service, which could indicate a regression.

netstat -tulnp | grep :113

6. Preventive Measures and Monitoring

Update security baselines to include disabling unnecessary services like identd. Implement checks in CI/CD pipelines to prevent the service from being inadvertently re-enabled. Maintain a sensible patch or configuration review cycle that fits the risk profile of your systems.

• Baselines: Update security baselines (e.g., CIS benchmarks) to include disabling identd.
• Pipelines: Add checks in CI/CD pipelines to ensure unnecessary services are not enabled during deployment.
• Asset and patch process: Review system configurations regularly for compliance with security standards.

7. Risks, Side Effects, and Roll Back

Disabling the identd service may impact applications that rely on it (though this is rare). If issues arise, re-enable the service to restore functionality.

• Risk or side effect 2: Disabling the service may cause unexpected behavior in certain network configurations.
• Roll back:
  1. Step 1: Enable the identd service using your operating system’s service management tool (e.g., systemctl enable identd on Linux).
  2. Step 2: Start the identd service using systemctl start identd.

8. References and Resources

• Vendor advisory or bulletin: No specific vendor advisory available for general identd service.
• NVD or CVE entry: CVE-2001-0876
• Product or platform documentation relevant to the fix: Consult your operating system’s documentation for instructions on disabling services.