CVE-2015-5470 in Recursor
Summary
by MITRE
The label decompression functionality in PowerDNS Recursor before 3.6.4 and 3.7.x before 3.7.3 and Authoritative (Auth) Server before 3.3.3 and 3.4.x before 3.4.5 allows remote attackers to cause a denial of service (CPU consumption or crash) via a request with a long name that refers to itself. NOTE: this vulnerability exists because of an incomplete fix for CVE-2015-1868.
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Analysis
by VulDB Data Team • 03/10/2018
The vulnerability described in CVE-2015-5470 represents a critical denial of service weakness affecting PowerDNS Recursor and Authoritative Server implementations. This flaw specifically targets the label decompression functionality within these DNS server components, creating a condition where maliciously crafted DNS requests can trigger excessive resource consumption or system crashes. The vulnerability emerged as an incomplete remediation for CVE-2015-1868, indicating that previous efforts to address similar issues were insufficient and created a persistent attack surface.
The technical mechanism behind this vulnerability involves the processing of DNS labels that contain self-referential naming structures. When a DNS request contains a name that refers to itself in a recursive manner, the decompression algorithm within PowerDNS fails to properly handle these circular references, leading to infinite loops or excessive CPU consumption during processing. This behavior occurs because the decompression logic does not adequately validate or limit the depth of label resolution, allowing attackers to craft requests that exploit this weakness. The vulnerability affects multiple versions of PowerDNS, including Recursor versions before 3.6.4 and 3.7.x before 3.7.3, as well as Authoritative Server versions before 3.3.3 and 3.4.x before 3.4.5, demonstrating the widespread nature of this implementation flaw.
The operational impact of CVE-2015-5470 extends beyond simple service disruption, potentially allowing attackers to consume significant system resources or cause complete system crashes through relatively simple network requests. This makes it particularly dangerous in production environments where DNS servers are critical infrastructure components, as attackers can effectively bring down entire DNS resolution services with minimal effort. The vulnerability's classification under CWE-400 indicates it involves an uncontrolled resource consumption issue, while its relationship to CVE-2015-1868 shows a pattern of incomplete security fixes that leave systems vulnerable to similar attack vectors. The continuous nature of the resource consumption can lead to sustained denial of service conditions that are difficult to detect and mitigate, as the malicious requests may appear legitimate at first glance.
Mitigation strategies for this vulnerability require immediate deployment of patched versions of PowerDNS software, specifically targeting the affected versions mentioned in the CVE description. Organizations should implement network-level controls to monitor and filter DNS requests that exhibit suspicious label structures or excessive recursion patterns. The implementation of rate limiting and request validation mechanisms can help prevent exploitation by limiting the number of recursive lookups that can be processed within a given timeframe. Additionally, network segmentation and access control measures should be employed to restrict direct access to DNS servers from untrusted networks. From an ATT&CK framework perspective, this vulnerability maps to techniques involving resource exhaustion and service disruption, with the attack chain typically beginning with reconnaissance to identify vulnerable DNS implementations followed by exploitation through crafted DNS queries. Regular security assessments and vulnerability scanning should be conducted to identify any remaining instances of unpatched systems, while incident response procedures should be established to quickly detect and respond to potential exploitation attempts.