Sniffing Technique: DNS Poisoning

Sniffing Technique: DNS Poisoning

What is DNS Poisoning?

DNS poisoning (also known as DNS cache poisoning or DNS spoofing) is a type of cyber attack where an attacker corrupts a DNS server's cache by injecting false DNS records. This causes the DNS server to return an incorrect IP address, diverting traffic to malicious websites.

Why is DNS Poisoning Important to Understand?

DNS poisoning is a critical concept in cybersecurity because:
- It allows attackers to redirect users to malicious websites
- It can bypass many security controls since the user believes they're visiting a legitimate site
- It can affect thousands of users if a public DNS server is compromised
- It enables large-scale phishing, malware distribution, and credential theft

How DNS Poisoning Works

1. Normal DNS Resolution: When you type a URL, your computer asks a DNS server to translate the domain name into an IP address.

2. The Attack Process:
- Attackers exploit vulnerabilities in DNS software
- They send forged DNS response packets before the legitimate response arrives
- The DNS server caches this false information
- Subsequent requests for that domain are directed to the attacker's IP address

3. Types of DNS Poisoning Attacks:
- Birthday Attack: Exploits probability to guess transaction IDs
- Kaminsky Attack: Exploits recursive DNS queries to poison entire domains
- Man-in-the-Middle: Intercepts DNS queries to provide malicious responses

Detection and Prevention

1. Detection Methods:
- DNS monitoring tools
- Unusual DNS traffic patterns
- Unexpected DNS record changes

2. Prevention Techniques:
- DNSSEC (DNS Security Extensions)
- DNS query randomization
- Regular DNS security audits
- Keep DNS software updated
- DNS traffic encryption

Exam Tips: Answering Questions on DNS Poisoning

1. Key Terminology:
- Be clear on the distinction between DNS poisoning, DNS hijacking, and pharming
- Understand transaction IDs and their role in DNS security
- Know what DNSSEC is and how it helps prevent poisoning

2. Common Question Types:
- Technical questions about the attack methodology
- Scenario-based questions where you need to identify DNS poisoning
- Questions about appropriate countermeasures
- Questions comparing DNS poisoning to other attack types

3. Response Strategy:
- For technical questions, focus on the manipulation of DNS records and caching
- For scenario questions, look for clues like users being redirected despite typing correct URLs
- When asked about countermeasures, prioritize DNSSEC, query randomization, and DNS monitoring
- Remember DNS poisoning is a passive sniffing technique as it redirects traffic rather than merely capturing it

4. Common Pitfalls:
- Mixing up DNS poisoning with ARP poisoning
- Focusing only on client-side solutions when DNS poisoning is primarily addressed at the server level
- Underestimating the scale of impact (it affects all users of the poisoned DNS server)

5. Sample Question Analysis:
"An attacker has modified DNS records to redirect banking website traffic. What technique is being used?" - Correct answer: DNS poisoning/DNS cache poisoning
- Reasoning: The question describes altering DNS records to redirect legitimate traffic, the core mechanism of DNS poisoning

Remember that DNS poisoning attacks the infrastructure of the internet itself, making it particularly dangerous. Focus on understanding both the technical mechanics and the broad security implications to excel in exam questions on this topic.