A Random Subdomain Attack, also known as a “Slow Drip” or “Domain Exhaustion” attack, is an attack method targeting the DNS infrastructure of a domain.
Overview:
In a Random Subdomain Attack, an attacker generates an overwhelming number of unique, random subdomains under a legitimate domain. These subdomains do not exist, but DNS resolvers attempt to resolve them, causing a high volume of unnecessary traffic.
Mechanics:
- Attack Initiation: The attacker generates DNS queries for random, non-existent subdomains of a target domain. For example, querying abcdef.example.com, ghijkl.example.com, and so on.
- DNS Query Flooding: These queries are repeatedly sent to the DNS resolver, flooding it with a large number of requests, all aiming at different subdomains of the target domain.
- Resolver Strain: Since these subdomains don’t exist, the recursive resolvers forward these queries to the authoritative DNS servers responsible for the target domain. This causes a significant load on both recursive and authoritative DNS servers.
- DNS Server Overload: The authoritative DNS servers become overwhelmed with requests to resolve non-existent subdomains, leading to increased latency, degradation in performance, or even a denial of service.
Purpose:
- Resource Exhaustion: this action consumes the resources of both recursive and authoritative DNS servers, leading to performance degradation or downtime.
- Disruption: To disrupt the legitimate functioning of the target domain by making its DNS infrastructure unresponsive.
Mitigation Strategies:
- Rate Limiting: Implement rate limiting on DNS servers to mitigate the flood of requests.
- DNS Firewall: Deploy DNS firewalls to filter out abnormal request patterns or known malicious query sources.
- Monitoring and Alerting: Monitor DNS traffic for unusual patterns and set up alerts to detect potential attacks early.
- Resilience: make your DNS infrastructure resilient by distributing the load across multiple servers and geographical locations.
Conclusion:
Random Subdomain Attacks are challenging to defend against due to the nature of DNS traffic and the legitimate need to resolve a high volume of queries. Improving monitoring, rate limiting, and infrastructure scaling, which are vital in mitigating such attacks, would help.
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