CVE-2016-7068 in PowerDNS
Summary
by MITRE
An issue has been found in PowerDNS before 3.4.11 and 4.0.2, and PowerDNS recursor before 3.7.4 and 4.0.4, allowing a remote, unauthenticated attacker to cause an abnormal CPU usage load on the PowerDNS server by sending crafted DNS queries, which might result in a partial denial of service if the system becomes overloaded. This issue is based on the fact that the PowerDNS server parses all records present in a query regardless of whether they are needed or even legitimate. A specially crafted query containing a large number of records can be used to take advantage of that behaviour.
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Analysis
by VulDB Data Team • 05/08/2023
The vulnerability identified as CVE-2016-7068 represents a significant denial of service weakness in PowerDNS server implementations across multiple versions. This flaw exists in both the authoritative DNS server and the recursor components, affecting versions prior to 3.4.11 and 4.0.2 for the server, and 3.7.4 and 4.0.4 for the recursor. The vulnerability stems from the server's parsing behavior where it processes all DNS records contained within incoming queries regardless of their necessity or legitimacy. This indiscriminate processing creates an exploitable condition that allows remote attackers to consume excessive CPU resources through carefully constructed malicious queries.
The technical mechanism behind this vulnerability involves the PowerDNS server's handling of DNS query packets that contain an excessive number of resource records. When processing these malformed queries, the server's parser does not implement any reasonable limits on the number of records it will examine or process. This behavior creates a resource exhaustion scenario where an attacker can send a single query containing thousands or even millions of DNS records, causing the server to spend considerable processing time on each record. The computational overhead grows linearly with the number of records, leading to significant CPU utilization spikes that can overwhelm the system's processing capabilities.
From an operational perspective, this vulnerability poses a substantial risk to DNS infrastructure reliability and availability. The partial denial of service condition can severely impact legitimate DNS resolution services, as the server becomes overwhelmed with processing malicious queries rather than serving legitimate client requests. Network administrators may observe unusual CPU load patterns, degraded response times, and potential service interruptions. The vulnerability is particularly dangerous because it requires no authentication or privileged access to exploit, making it accessible to any remote attacker with network connectivity to the affected DNS server. This characteristic aligns with ATT&CK technique T1499.004 for network denial of service attacks and represents a classic example of resource exhaustion exploitation patterns.
The vulnerability's impact is further amplified by its presence in widely deployed DNS server software, affecting organizations that rely on PowerDNS for critical infrastructure services. The issue demonstrates poor input validation practices and highlights the importance of implementing reasonable limits on resource consumption during parsing operations. Organizations should consider implementing rate limiting mechanisms, query size restrictions, and monitoring for unusual CPU utilization patterns as part of their defensive strategies. The flaw also underscores the need for proper security testing of parsing logic and the importance of adhering to CWE guidelines regarding resource management and input validation to prevent similar issues in DNS server implementations.