CVE-2016-7072 in Authoritative Server
Summary
by MITRE
An issue has been found in PowerDNS Authoritative Server before 3.4.11 and 4.0.2 allowing a remote, unauthenticated attacker to cause a denial of service by opening a large number of TCP connections to the web server. If the web server runs out of file descriptors, it triggers an exception and terminates the whole PowerDNS process. While it's more complicated for an unauthorized attacker to make the web server run out of file descriptors since its connection will be closed just after being accepted, it might still be possible.
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Analysis
by VulDB Data Team • 05/08/2023
The vulnerability identified as CVE-2016-7072 represents a significant denial of service weakness in PowerDNS Authoritative Server versions prior to 3.4.11 and 4.0.2. This flaw exposes the web server component to remote exploitation by unauthenticated attackers who can systematically open a large volume of TCP connections to exhaust system resources. The attack vector specifically targets the web server's file descriptor limits, which serve as critical system resources for managing network connections and I/O operations. When the web server reaches its maximum file descriptor capacity, the system encounters an exception that results in the complete termination of the PowerDNS process, effectively rendering the DNS service unavailable to legitimate users.
The technical implementation of this vulnerability stems from inadequate connection handling mechanisms within the web server component of PowerDNS. The flaw operates through a resource exhaustion attack pattern where an attacker establishes numerous concurrent TCP connections to the web server interface. While the system architecture includes basic connection management that closes connections shortly after acceptance, this protective mechanism proves insufficient against sustained attack efforts. The vulnerability demonstrates poor resource management practices that fail to implement proper connection rate limiting, connection timeouts, or connection pooling mechanisms. This weakness allows attackers to consume system resources faster than the system can recover, ultimately leading to process termination and complete service disruption.
From an operational impact perspective, this vulnerability creates a severe availability risk for organizations relying on PowerDNS Authoritative Server for their DNS infrastructure. The denial of service condition affects not only the web server functionality but also potentially impacts the entire DNS resolution process, as the PowerDNS process termination disrupts all active DNS services. The attack requires minimal privileges and can be executed remotely without authentication, making it particularly dangerous for publicly accessible DNS servers. Network administrators may experience extended downtime while investigating and resolving the service disruption, potentially affecting thousands of DNS queries and causing cascading effects throughout dependent systems and applications that rely on DNS resolution.
The vulnerability aligns with CWE-400, which addresses "Uncontrolled Resource Consumption" and specifically targets resource exhaustion scenarios that can lead to system instability and service disruption. From the MITRE ATT&CK framework perspective, this represents a denial of service attack technique that falls under the category of resource exhaustion, where attackers leverage system limitations to prevent legitimate use of services. The attack pattern demonstrates characteristics of a resource exhaustion attack that can be classified as a persistent threat requiring continuous monitoring and mitigation. Organizations should implement connection rate limiting, connection timeout configurations, and file descriptor limit adjustments as immediate defensive measures to protect against this vulnerability.
Mitigation strategies for CVE-2016-7072 primarily involve upgrading to PowerDNS Authoritative Server versions 3.4.11 or 4.0.2, which contain the necessary patches to address the connection handling issues. Additionally, system administrators should implement proper network-level protections including firewall rules that limit connection rates from individual IP addresses, connection timeout configurations that prevent long-lived connections from consuming resources, and monitoring systems that detect unusual connection patterns. Network segmentation and access control measures can help reduce the attack surface by limiting direct access to the web server interface. Regular system auditing and resource monitoring should be implemented to detect early signs of resource exhaustion attacks, while maintaining adequate file descriptor limits to prevent system-level failures. These measures collectively address both the immediate vulnerability and provide broader protection against similar resource exhaustion threats in the DNS infrastructure.