ReadyNet WRT300N-DD devices with firmware 1.0.26 use the same source port number for every DNS query, which makes it easier for remote attackers to spoof responses by selecting that number for the destination port.
ReadyNet WRT300N-DD routers with firmware 1.0.26 are vulnerable to DNS spoofing attacks due to a flaw in how they handle DNS queries. This vulnerability allows attackers to redirect network traffic to malicious servers, potentially leading to data theft, malware infection, and network compromise.
Step 1: Target Identification: The attacker identifies a vulnerable ReadyNet WRT300N-DD router running firmware 1.0.26.
Step 2: DNS Query Observation: The attacker monitors the network traffic to observe the DNS queries originating from the target router. This is often done by passively sniffing the network or actively querying the router's DNS server.
Step 3: Source Port Determination: The attacker determines that the router consistently uses the same source port for all DNS queries (e.g., port 53).
Step 4: Malicious DNS Response Crafting: The attacker crafts a malicious DNS response. This response includes the same transaction ID as the legitimate DNS query and the known source port of the target router.
Step 5: Response Injection: The attacker sends the crafted malicious DNS response to the target router's DNS server, attempting to inject the malicious response before the legitimate response arrives.
Step 6: DNS Cache Poisoning: If successful, the malicious DNS response is cached by the router, associating a malicious IP address with a legitimate domain name.
Step 7: Traffic Redirection: Subsequent traffic destined for the spoofed domain is redirected to the attacker-controlled server, enabling data theft, malware distribution, or other malicious activities.
The vulnerability stems from the router's consistent use of the same source port for all DNS queries. This predictable behavior significantly reduces the entropy required for a successful DNS spoofing attack. The router's firmware lacks proper randomization of the source port, making it trivial for an attacker to guess the correct destination port for a malicious DNS response. This predictability allows an attacker to craft a forged DNS response with a matching transaction ID and the known source port, effectively poisoning the router's DNS cache and redirecting traffic.