DDoS attacks remain one of the most pervasive and damaging tactics employed by cybercriminals. These attacks aim to overwhelm a network or server with excessive traffic, rendering it unavailable to legitimate users. While traditional DDoS attacks like SYN floods or UDP floods are well-known, there’s another stealthy and persistent form of DNS-based attack that deserves attention — the DNS Water Torture DDoS attack.
What is a DNS Water Torture Attack?
The DNS Water Torture DDoS attack is a type of DNS-based attack where an attacker sends a constant, steady stream of DNS queries to a targeted server. These queries often involve non-existent or low-value domains, or they may include subdomain variations of legitimate domains that are not frequently accessed.
How the DNS Water Torture Attack Works
In a DNS Water Torture attack, the attacker doesn’t flood the DNS server with massive volumes of queries all at once. Instead, they send small, continuous requests for domains that either do not exist or are not frequently accessed. These queries may be spaced out, coming in at regular intervals or with slight variations to look like legitimate traffic.
Over time, the DNS server becomes exhausted by the ongoing query processing, which results in degraded performance, delays in responding to legitimate DNS queries, or even complete failure.
Non-existent Domains: The attacker may request random or non-existent domain names (e.g., nonexistent12345.com), which forces the server to generate an NXDOMAIN (Non-Existent Domain) response.
Subdomain Variations: The attacker might query subdomains of a legitimate domain, where those subdomains are either invalid or do not exist (e.g., random.example.com), causing the DNS server to handle multiple, unnecessary queries.
The Impact of a DNS Water Torture Attack
The primary goal of a DNS Water Torture attack is to exhaust a DNS server’s resources, leading to performance degradation or failure. While the attack is stealthier than traditional DDoS attacks, its effects can be just as damaging. The consequences of a successful DNS Water Torture attack include:
- Slow DNS Resolution: As the DNS server is consumed by constant queries, its ability to process legitimate DNS lookups slows down, causing delays for users trying to access websites or services.
- Increased Server Load: The attack increases the load on the DNS server by continuously processing queries, which can cause it to become unresponsive. This increases operational costs as server resources become depleted.
- Denial of Service: If the DNS server is overwhelmed, it may fail to resolve DNS queries entirely, leading to complete service disruption for users attempting to access affected websites or services.
- Network Congestion: The consistent flow of DNS traffic not only affects the targeted DNS server but can also cause network congestion, further impairing the performance of other services and applications across the network.
Effective Ways to Mitigate the DNS Water Torture Attack
Because of the continuous and subtle nature of the DNS Water Torture attack, it requires a proactive approach to detection and mitigation.
Rate Limiting
Implementing DNS rate limiting can help restrict the number of queries that can be processed by the server from a single IP address within a specific time period. This prevents the attacker from overwhelming the server with excessive requests, especially when dealing with a continuous query stream.
DNS Query Filtering
DNS query filtering can help block traffic from suspicious sources or traffic that matches known patterns of attacks. For instance, using DNS firewalls or intrusion detection systems (IDS) can help identify and filter out queries for non-existent or low-value domains.
Caching and Load Balancing
By caching resolved DNS queries and using multiple DNS servers, organizations can reduce the load on individual DNS servers. Additionally, load balancing ensures that the traffic is distributed across multiple servers, preventing any single server from becoming overwhelmed during an attack.
Anycast DNS
Anycast is a routing method that involves deploying multiple DNS servers across different geographic locations. All these servers share the same IP address, and traffic is routed to the nearest server. This improves the resilience of DNS infrastructure and helps distribute the load in case of an attack.
Continuous Traffic Monitoring
Continuous monitoring of DNS traffic allows security teams to detect abnormal patterns or unexpected spikes in traffic early on. The presence of unusually high volumes of DNS queries can serve as a red flag for a potential DNS Water Torture attack, enabling teams to act swiftly before the attack causes major disruption.
Leveraging DNSSEC Solutions
Many organizations choose to rely on specialized DNSSEC capabilities on AppTrana WAAP to defend against DNS attacks. These services provide real-time traffic analysis, filtering, and mitigation capabilities designed specifically to address DNS-based DDoS attacks, including DNS Water Torture.
