CVE-2016-5426 in PowerDNS
Summary
by MITRE
PowerDNS (aka pdns) Authoritative Server before 3.4.10 allows remote attackers to cause a denial of service (backend CPU consumption) via a long qname.
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Analysis
by VulDB Data Team • 09/15/2022
PowerDNS authoritative server versions prior to 3.4.10 contain a critical denial of service vulnerability that stems from inadequate handling of excessively long query names. This vulnerability manifests when remote attackers submit malformed DNS queries with extremely long qname parameters, causing the server to consume excessive backend CPU resources during processing. The flaw exists in the server's query name validation and processing logic, where it fails to implement proper bounds checking on incoming query names. When processing these long query names, the server enters into computationally expensive operations that can lead to complete system resource exhaustion and service unavailability.
The technical implementation of this vulnerability involves the server's recursive processing of DNS query names without adequate input sanitization. Attackers can craft DNS queries with qname lengths that far exceed normal DNS query parameters, triggering inefficient string processing routines within the PowerDNS backend. This behavior aligns with CWE-770, which addresses allocation of resources without proper limits, and represents a classic example of a resource exhaustion attack. The vulnerability operates at the application layer and can be exploited through standard DNS protocol interactions, making it particularly dangerous as it requires no authentication or specialized privileges to execute.
The operational impact of CVE-2016-5426 extends beyond simple service disruption to potentially compromise entire DNS infrastructure availability. When exploited, the vulnerability causes the authoritative server to consume 100% CPU resources for extended periods, effectively rendering the DNS service unusable for legitimate queries. This creates cascading effects throughout network infrastructure that relies on the affected DNS server, potentially impacting thousands of downstream systems and applications. The attack can be executed remotely with minimal resources, making it an attractive vector for denial of service attacks against critical infrastructure. Organizations using vulnerable PowerDNS versions face significant risk of service degradation or complete outages, particularly during high-traffic periods.
Mitigation strategies for this vulnerability require immediate patching of PowerDNS servers to version 3.4.10 or later, which includes proper qname length validation and resource limiting mechanisms. Network administrators should implement rate limiting and query length restrictions at the network perimeter to prevent exploitation attempts from reaching the authoritative server. Additionally, monitoring systems should be configured to detect unusual CPU consumption patterns that may indicate exploitation attempts. The vulnerability demonstrates the importance of implementing proper input validation and resource management practices, aligning with ATT&CK technique T1499.004 for network denial of service attacks. Organizations should also consider implementing DNS query filtering and establishing incident response procedures to quickly identify and respond to potential exploitation attempts.