IP Address Blocklist: Troubleshooting

TL;DR

A block of IP addresses is being blocked because they’re associated with malicious activity (spam, hacking attempts, etc.). This guide helps you identify the source of the blocklist and how to resolve it. Common causes include shared hosting issues, compromised accounts, or legitimate users flagged incorrectly.

1. Identify Where the Blocklist is Applied

1. Web Server (e.g., Apache, Nginx): Check your server configuration files (.htaccess for Apache, nginx.conf for Nginx) for rules blocking IP ranges.
2. Firewall (e.g., iptables, ufw, pfSense): Examine firewall rules to see if any blocks are in place. Use commands like sudo iptables -L or sudo ufw status verbose to list current rules.
3. Content Delivery Network (CDN) (e.g., Cloudflare, Akamai): CDNs often have their own blocklist features. Log into your CDN account and check the security settings.
4. Web Application Firewall (WAF) (e.g., ModSecurity): WAFs can automatically block IPs based on detected threats. Review your WAF logs and configuration.
5. Email Server: If email is affected, check your mail server’s spam filters or blacklists.

2. Determine the Source of the Blocklist

1. Check Logs: Examine logs from the system where the blocklist is applied (web server, firewall, WAF). Look for entries related to the blocked IP addresses and any associated error messages or reasons for blocking.
2. Reverse DNS Lookup: Use a reverse DNS lookup tool (e.g., MXToolbox) on the blocked IPs to see if they are associated with known malicious hosts.
3. IP Reputation Checkers: Utilize online IP reputation checkers (e.g., AbuseIPDB, Talos Intelligence) to see if the IPs are listed on public blocklists.
4. Shared Hosting: If you’re using shared hosting, another user on the same server might be causing problems and getting the entire IP range blocked. Contact your hosting provider for assistance.

3. Resolve the Blocklist Issue

1. If a Legitimate User is Blocked:
• Whitelist the IP Address: Add the user’s IP address to an allow list (whitelist) in your firewall, WAF, or CDN configuration. Be cautious when whitelisting; only whitelist IPs you trust.
• Review Blocking Rules: If possible, adjust blocking rules to be less aggressive and avoid false positives.
2. If the Blocklist is Due to Malicious Activity:
• Investigate Compromised Accounts: Check for any signs of compromised user accounts (unusual login activity, unauthorized changes). Change passwords immediately if necessary.
• Scan for Malware: Run a full system scan with an up-to-date antivirus/antimalware solution.
• Strengthen cyber security Measures: Implement stronger password policies, enable two-factor authentication, and keep your software updated.
• Contact Your Hosting Provider: If you suspect a server-level compromise, contact your hosting provider for assistance.
3. If the Blocklist is from Shared Hosting:
• Contact Your Hosting Provider: Report the issue to your hosting provider and request they investigate the source of the problem on their server. They may need to block the offending account or take other measures.
• Consider a Dedicated Server/VPS: If shared hosting is consistently causing issues, consider upgrading to a dedicated server or Virtual Private Server (VPS) for more control over your environment.

4. Prevent Future Blocklists

1. Regular Security Audits: Conduct regular security audits of your systems and applications to identify vulnerabilities.
2. Keep Software Updated: Keep all software (operating system, web server, applications) up-to-date with the latest security patches.
3. Monitor Logs Regularly: Monitor logs for suspicious activity and investigate any anomalies promptly.
4. Implement a WAF: Use a Web Application Firewall to protect against common web attacks.