DNS Spoofing / Cache Poisoning

What is DNS Spoofing / Cache Poisoning?

DNS spoofing, also known as DNS cache poisoning, is a cyber attack in which false Domain Name System (DNS) information is introduced into a DNS resolver's cache. This causes the resolver to return an incorrect IP address, diverting traffic to malicious websites instead of the legitimate ones users intend to visit.

The attack exploits vulnerabilities in the DNS protocol to corrupt the cache of DNS resolvers, making them serve fraudulent DNS responses to unsuspecting users.

How DNS Spoofing Works

The attack typically follows these steps:

1. Target Identification: Attacker identifies a vulnerable DNS resolver
2. Query Interception: Attacker intercepts or predicts DNS queries
3. False Response: Attacker sends a forged DNS response before the legitimate one arrives
4. Cache Poisoning: The resolver caches the false DNS information
5. Traffic Redirection: Users are redirected to malicious websites
6. Exploitation: Attacker exploits the redirected traffic (phishing, malware distribution, etc.)

Types of DNS Spoofing Attacks

1. Traditional Cache Poisoning

• Exploits race conditions in DNS resolvers
• Attacker floods resolver with fake responses
• First response to arrive gets cached

2. Kaminsky Attack (2008)

• Discovered by security researcher Dan Kaminsky
• Exploits predictable transaction IDs in DNS queries
• Allows attackers to poison entire domains
• Led to widespread adoption of DNS security measures

3. Man-in-the-Middle (MITM) DNS Spoofing

• Attacker intercepts communication between user and DNS resolver
• Modifies DNS responses in real-time
• Doesn't require cache poisoning

4. DNS Hijacking

• Attacker gains control of DNS settings
• Can be done through malware, router compromise, or registrar hijacking
• Redirects all traffic for a domain

Real-World Examples

1. Brazilian Bank Attack (2016): Attackers used DNS spoofing to redirect customers to phishing sites, stealing login credentials
2. Netflix Phishing (2017): Users were redirected to fake Netflix login pages
3. Google Malaysia (2015): Users in Malaysia were redirected to a hacker's page
4. NY Times Attack (2013): Syrian Electronic Army redirected NYTimes.com to their own server

Impact of DNS Spoofing

• Phishing: Users enter credentials on fake websites
• Malware Distribution: Users download malicious software
• Data Theft: Sensitive information is captured
• Session Hijacking: Attackers take over user sessions
• Reputation Damage: Legitimate businesses lose trust
• Financial Loss: Fraudulent transactions and stolen funds
• Service Disruption: Legitimate services become inaccessible

Detection Methods

• Unexpected redirects: Being sent to different websites than intended
• SSL certificate warnings: Browser warnings about invalid certificates
• Inconsistent DNS responses: Different IP addresses for the same domain
• Network monitoring: Unusual DNS query patterns
• DNSSEC validation failures: Failed cryptographic verification
• Log analysis: Unexpected changes in DNS resolution patterns

Prevention and Mitigation

For DNS Administrators:

• Implement DNSSEC: Digitally sign DNS records to ensure authenticity
• Use random transaction IDs: Make it harder to predict query IDs
• Source port randomization: Randomize source ports for DNS queries
• Limit recursive queries: Restrict recursion to authorized clients
• Regular updates: Keep DNS software updated
• Monitor DNS traffic: Detect unusual patterns
• Disable zone transfers: Restrict AXFR to authorized servers

For End Users:

• Use secure DNS resolvers: Such as Google DNS (8.8.8.8) or Cloudflare (1.1.1.1)
• Verify SSL certificates: Check for valid certificates on websites
• Use VPNs: Encrypt traffic to prevent interception
• Keep software updated: Patch vulnerabilities in operating systems and browsers
• Use security software: Install antivirus and anti-malware solutions
• Be cautious with links: Verify URLs before clicking
• Check for HTTPS: Ensure websites use secure connections

For Website Owners:

• Implement HSTS: Force browsers to use HTTPS only
• Use CAA records: Specify which CAs can issue certificates
• Monitor DNS changes: Set up alerts for unauthorized modifications
• Implement multi-factor authentication: For DNS management interfaces
• Regular audits: Review DNS configurations periodically

DNSSEC: The Ultimate Protection

DNS Security Extensions (DNSSEC) provides cryptographic authentication for DNS data:

• Digital signatures: DNS records are signed with private keys
• Chain of trust: Verification starts from the root zone
• Data integrity: Ensures responses haven't been tampered with
• Authenticated denial: Proves when a domain doesn't exist

DNSSEC prevents cache poisoning by ensuring that DNS responses come from legitimate sources.

Best Practices for Organizations

1. Deploy DNSSEC for all domains
2. Use reputable DNS providers with strong security measures
3. Implement DNS monitoring to detect anomalies
4. Educate employees about DNS security risks
5. Regular security audits of DNS infrastructure
6. Implement rate limiting to prevent query flooding
7. Use Anycast DNS for improved resilience
8. Maintain redundancy with multiple DNS providers
9. Secure DNS management interfaces with strong authentication
10. Keep software updated to patch vulnerabilities

Interesting Facts

• The first major DNS cache poisoning attack was documented in 1997
• DNS spoofing is often used in conjunction with phishing attacks
• Some governments have used DNS spoofing for censorship
• The Kaminsky attack demonstrated how vulnerable DNS was before DNSSEC
• DNS spoofing can be used for "drive-by pharming" attacks
• Some malware families specialize in DNS hijacking
• DNS spoofing can affect not just websites but also email and other services
• The average cost of a DNS attack is over $1 million for enterprises