CVE-2016-5427 in PowerDNS
Summary
by MITRE
PowerDNS (aka pdns) Authoritative Server before 3.4.10 does not properly handle a . (dot) inside labels, which allows remote attackers to cause a denial of service (backend CPU consumption) via a crafted DNS query.
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Analysis
by VulDB Data Team • 09/15/2022
The vulnerability identified as CVE-2016-5427 affects PowerDNS Authoritative Server versions prior to 3.4.10, representing a significant denial of service weakness that exploits improper handling of dot characters within DNS labels. This flaw exists within the core DNS processing logic where the server fails to correctly parse domain names containing dots within individual labels rather than as separators between labels. The issue stems from the server's insufficient validation and sanitization of DNS query structures, particularly when processing domain names that contain embedded dots within label boundaries. Such malformed DNS queries can cause the authoritative server to enter into inefficient processing loops or consume excessive computational resources while attempting to resolve these malformed queries.
The technical exploitation of this vulnerability occurs when a remote attacker crafts DNS queries containing dots within labels, which the vulnerable PowerDNS server processes without proper safeguards. The server's parsing mechanism becomes overwhelmed as it attempts to handle these malformed domain names, leading to excessive CPU utilization and potential system resource exhaustion. This behavior directly impacts the server's ability to respond to legitimate DNS queries, effectively creating a denial of service condition that can be triggered by any external party capable of sending DNS queries to the affected server. The vulnerability demonstrates a classic case of insufficient input validation where the system fails to properly sanitize or reject malformed DNS constructs before processing them.
From an operational perspective, this vulnerability presents a severe risk to DNS infrastructure availability and reliability, particularly for organizations relying on PowerDNS as their authoritative name server. The impact extends beyond simple service disruption as the excessive CPU consumption can cascade into broader network performance issues, affecting not only the vulnerable server but potentially impacting downstream systems that depend on its responsiveness. Attackers can exploit this weakness with minimal resources and technical expertise, making it particularly dangerous for publicly accessible DNS servers. The vulnerability also represents a failure in the principle of least privilege and input validation, as the server should reject malformed queries rather than attempting to process them and consuming resources in the process.
Mitigation strategies for CVE-2016-5427 primarily involve upgrading to PowerDNS version 3.4.10 or later, which includes proper handling of dot characters within DNS labels. Organizations should also implement DNS query filtering mechanisms to detect and block malformed queries before they reach the authoritative server, leveraging tools such as DNS firewalls or rate limiting systems. Network administrators should monitor DNS server performance metrics closely to detect unusual CPU utilization patterns that may indicate exploitation attempts. Additionally, implementing proper DNS security measures including dnssec validation and query logging can help identify and respond to such attacks. This vulnerability aligns with CWE-20, which addresses improper input validation, and maps to ATT&CK technique T1499.004 for denial of service attacks. Organizations should also consider implementing network segmentation and access controls to limit exposure of vulnerable DNS servers to untrusted networks, reducing the attack surface for this specific vulnerability.