CVE-2022-33989 in dproxy-nexgen
Summary
by MITRE • 08/15/2022
dproxy-nexgen (aka dproxy nexgen) uses a static UDP source port (selected randomly only at boot time) in upstream queries sent to DNS resolvers. This allows DNS cache poisoning because there is not enough entropy to prevent traffic injection attacks.
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Analysis
by VulDB Data Team • 09/11/2022
The vulnerability identified as CVE-2022-33989 affects dproxy-nexgen, a DNS proxy implementation that serves as an intermediary between client devices and DNS resolvers. This system operates by forwarding DNS queries from local clients to upstream DNS servers while maintaining a specific operational model that introduces significant security weaknesses. The primary flaw lies in the deterministic nature of the source port selection mechanism used during outbound DNS communications, which creates predictable network traffic patterns that adversaries can exploit to manipulate DNS resolution outcomes.
The technical implementation of this vulnerability stems from the use of a static UDP source port that is randomly selected only during system initialization rather than being dynamically generated for each transaction. This approach fundamentally violates the cryptographic principle of sufficient entropy in network communications, as the same source port is reused for all upstream DNS queries throughout the system's operational lifetime. The deterministic nature of this port selection creates a predictable communication pattern that allows attackers positioned within the network to inject malicious DNS responses that can be accepted by the vulnerable system. This weakness directly maps to CWE-330, which addresses insufficient entropy in random number generation, and represents a critical failure in the system's ability to maintain secure communication channels.
The operational impact of this vulnerability extends beyond simple cache poisoning, as it enables sophisticated man-in-the-middle attacks that can redirect traffic to malicious endpoints. An attacker with network access between the vulnerable dproxy-nexgen system and its upstream DNS resolvers can exploit this weakness to inject forged DNS responses that appear legitimate due to the predictable source port characteristics. This creates opportunities for credential theft, malware distribution, and service disruption attacks that can compromise entire network infrastructures. The vulnerability particularly affects environments where DNS security is paramount, such as enterprise networks, cloud deployments, and systems handling sensitive data, where the ability to manipulate DNS resolution can lead to significant business and security implications.
Mitigation strategies for this vulnerability require immediate implementation of dynamic source port allocation mechanisms that ensure sufficient entropy in network communications. Organizations should upgrade their dproxy-nexgen implementations to versions that utilize randomized source port selection for each DNS transaction, thereby eliminating the predictable patterns that enable cache poisoning attacks. Network administrators should also implement additional security controls such as DNS Security Extensions (DNSSEC) to provide cryptographic validation of DNS responses, and monitor for suspicious DNS traffic patterns that may indicate exploitation attempts. The remediation process should include network segmentation to limit access to DNS proxy systems and regular security audits to ensure that source port randomization is properly implemented. This vulnerability demonstrates the critical importance of entropy in network security implementations and aligns with ATT&CK technique T1071.004, which covers DNS tunneling and manipulation, highlighting the need for robust network protocol implementations that resist traffic injection attacks through predictable communication patterns.