How to remediate – ICMP Timestamp Request Remote Date Disclosure

1. Introduction

The ICMP Timestamp Request vulnerability (CVE-1999-0524) allows an attacker to determine the exact time set on a remote host. This information can assist in defeating time-based authentication protocols, potentially compromising system security. Systems running any TCP/IP stack are usually affected, but Windows Vista / 7 / 2008 / 2008 R2 systems return deliberately incorrect timestamps. Impact is likely to be low on confidentiality and integrity, with a medium risk to availability if time-based services are disrupted.

2. Technical Explanation

The remote host responds to ICMP timestamp requests, revealing its system time. An attacker sends an ICMP timestamp request packet; the response contains the current date and time as set on the target machine. This allows attackers to potentially bypass authentication mechanisms that rely on accurate time synchronization. CVE-1999-0524 describes this vulnerability. A simple example is using the `ping` command with the `-t` option (on some systems) or dedicated network tools to send timestamp requests and analyse responses.

• Root cause: The host answers ICMP timestamp requests without proper validation or filtering, exposing system time information.
• Exploit mechanism: An attacker sends an ICMP timestamp request packet to the target machine and analyses the response for the current date and time.
• Scope: All systems running a TCP/IP stack are potentially affected. Windows Vista / 7 / 2008 / 2008 R2 return deliberately incorrect timestamps, but may still be useful in some scenarios.

3. Detection and Assessment

Confirming vulnerability involves checking if the system responds to ICMP timestamp requests. A quick check is using `ping` with the `-t` option (if supported). Thorough assessment requires network packet capture and analysis of responses.

• Quick checks: Use ping -t on Windows or a similar tool to send ICMP timestamp requests. If replies are received, the system is likely vulnerable.
• Scanning: Nessus plugin ID 10857 can detect this vulnerability. This is an example only.
• Logs and evidence: Network traffic captures will show responses to ICMP timestamp request packets (type 13).

ping -t 

4. Solution / Remediation Steps

The recommended solution is to filter out ICMP timestamp requests and replies at the firewall or network device level. This prevents attackers from querying the system time.

4.1 Preparation

• Ensure you have a rollback plan to re-enable ICMP if needed (though this is generally discouraged). A change window may be needed depending on network infrastructure policies.

4.2 Implementation

1. Step 1: Configure your firewall or router to block incoming ICMP timestamp requests (type 13).
2. Step 2: Configure your firewall or router to block outgoing ICMP timestamp replies (type 14).

4.3 Config or Code Example

Before

# No specific ICMP filtering rules configured

After

# Example using iptables (Linux)
iptables -A INPUT -p icmp --icmp-type timestamp-request -j DROP
iptables -A OUTPUT -p icmp --icmp-type timestamp-reply -j DROP
# Example using Windows Firewall with Advanced Security:
New-NetFirewallRule -DisplayName "Block ICMP Timestamp Requests" -Direction Inbound -Protocol ICMPv4 -ICMPType 13 -Action Block
New-NetFirewallRule -DisplayName "Block ICMP Timestamp Replies" -Direction Outbound -Protocol ICMPv4 -ICMPType 14 -Action Block

4.4 Security Practices Relevant to This Vulnerability

Network segmentation and least privilege can reduce the impact of this vulnerability. Input validation is also relevant, although directly applying it to ICMP packets is less common than at application layers. A robust patch cadence ensures systems are updated with security fixes.

• Practice 1: Network segmentation limits the reach of attackers if they compromise a system.
• Practice 2: Least privilege reduces the impact if an attacker gains access to time information.

4.5 Automation (Optional)

If using infrastructure-as-code, ICMP filtering rules can be automated. The following example uses Ansible:

---
- hosts: firewalls
  tasks:
    - name: Block ICMP Timestamp Requests and Replies
      iptables:
        chain: INPUT
        protocol: icmp
        icmp_type: timestamp-request
        jump: DROP
    - name: Block ICMP Timestamp Replies
      iptables:
        chain: OUTPUT
        protocol: icmp
        icmp_type: timestamp-reply
        jump: DROP

5. Verification / Validation

Confirm the fix by attempting to send an ICMP timestamp request and verifying no response is received. Re-test with `ping -t` or a similar tool. Ensure basic network connectivity remains functional.

• Post-fix check: Run ping -t . No replies should be received.
• Re-test: Repeat the initial detection method (e.g., `ping -t`) to confirm no responses are now returned.
• Smoke test: Verify basic network connectivity by pinging a known good host or accessing essential services.
• Monitoring: Monitor firewall logs for blocked ICMP timestamp requests and replies as an example of regression detection.

ping -t  # No response expected

6. Preventive Measures and Monitoring

Update security baselines to include ICMP filtering rules. Implement CI/CD pipelines with SAST or SCA tools to identify insecure configurations. Maintain a regular patch review cycle for all systems. For example, implement CIS control 10: Configure Audit Logging.

• Baselines: Update your network device configuration baseline to enforce ICMP filtering.
• Pipelines: Include checks in deployment pipelines to prevent the re-introduction of insecure configurations.
• Asset and patch process: Review system configurations regularly for compliance with security standards.

7. Risks, Side Effects, and Roll Back

• Risk or side effect 1: Blocking ICMP may affect network troubleshooting tools that rely on it.
• Risk or side effect 2: Some monitoring systems might use ICMP for basic reachability checks.
• Roll back:
  1. Step 1: Remove the firewall rules blocking incoming ICMP timestamp requests (type 13).
  2. Step 2: Remove the firewall rules blocking outgoing ICMP timestamp replies (type 14).

8. References and Resources

• Vendor advisory or bulletin: No specific vendor advisory available for this general vulnerability.
• NVD or CVE entry: CVE-1999-052