Source: cret@cert.org
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 due to predictable source port usage. This allows attackers to redirect network traffic to malicious servers, potentially leading to data theft or network compromise. The vulnerability is easily exploitable, posing a significant risk to affected networks.
Step 1: Target Identification: Identify a ReadyNet WRT300N-DD router with firmware 1.0.26. Step 2: DNS Query Observation: Monitor the network traffic to determine the source port the router uses for DNS queries. This is likely a consistent, non-random port. Step 3: Craft Malicious DNS Response: Construct a malicious DNS response packet. This packet must contain the same transaction ID as the legitimate DNS query and the predicted destination port (the router's source port). The response should point to a malicious IP address controlled by the attacker. Step 4: Timing Attack: Send the crafted DNS response to the router before the legitimate DNS response arrives. The attacker aims to have their malicious response processed first. Step 5: Traffic Redirection: If successful, the router will cache the malicious DNS record. Subsequent traffic intended for the legitimate domain will be redirected to the attacker's controlled IP address.
The vulnerability stems from a design flaw in the ReadyNet WRT300N-DD's DNS client implementation. The device consistently uses the same source port for all DNS queries. This lack of source port randomization makes it trivial for an attacker to predict the source port used by the router when it sends a DNS query. By crafting a malicious DNS response with the predicted destination port and the correct transaction ID, an attacker can successfully spoof the router's DNS resolution, redirecting traffic to a controlled server. The root cause is the absence of any randomness in the source port selection process, allowing for predictable responses.
While no specific APT groups are directly linked to this vulnerability, the ease of exploitation makes it attractive to various threat actors. This type of vulnerability is often used by attackers to establish a foothold for further attacks, such as malware distribution or data exfiltration. CISA KEV status: Not listed.
Network traffic analysis: Examine DNS query/response patterns for consistent source ports from ReadyNet WRT300N-DD devices.
IDS/IPS signatures: Implement signatures to detect DNS responses with spoofed source ports and malicious IP addresses.
Log analysis: Review DNS server logs for unusual traffic patterns or suspicious domain resolutions originating from affected devices.
Forensic analysis: Examine router configuration files for evidence of DNS server manipulation.
Upgrade firmware: Upgrade to a patched firmware version (if available). Check the ReadyNet website for updates. This is the primary and most effective remediation.
Network segmentation: Isolate the affected router from critical network segments to limit the impact of a successful exploit.
DNS server hardening: Implement DNSSEC to verify the authenticity of DNS responses. This mitigates the impact of DNS spoofing attacks.
Monitor DNS traffic: Regularly monitor DNS traffic for suspicious activity, such as unexpected domain resolutions or traffic redirection.
Change default credentials: If the router's web interface is accessible, change the default administrator credentials to prevent unauthorized access and configuration changes.