CVE-2016-6173 in nsd
Summary
by MITRE
NSD before 4.1.11 allows remote DNS master servers to cause a denial of service (/tmp disk consumption and slave server crash) via a zone transfer with unlimited data.
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Analysis
by VulDB Data Team • 11/12/2022
The vulnerability identified as CVE-2016-6173 affects the NSD DNS server software version 4.1.10 and earlier, presenting a significant denial of service risk that can be exploited by remote master DNS servers. This flaw stems from inadequate handling of zone transfer operations, specifically when dealing with unlimited data payloads that can be transmitted during the zone transfer process. The vulnerability manifests when a master DNS server initiates a zone transfer to a slave server running an affected version of NSD, causing the slave server to consume excessive disk space in the /tmp directory while simultaneously crashing the slave server itself. The technical root cause lies in the insufficient validation and resource management during zone transfer operations, where the software fails to properly limit or handle large data transfers that could potentially exhaust available storage resources.
The operational impact of this vulnerability extends beyond simple service disruption to encompass potential system instability and resource exhaustion that could affect other services running on the same host system. When exploited, the vulnerability causes the slave server to rapidly consume disk space in the /tmp partition, which often serves as a temporary storage area for various system processes and applications. This aggressive consumption of temporary storage space can lead to cascading failures where other system components that rely on the /tmp directory become unavailable or crash. Additionally, the slave server crash creates a complete denial of service scenario for the affected DNS zone, rendering it inaccessible to legitimate clients and potentially disrupting critical network services that depend on DNS resolution. The vulnerability is particularly dangerous because it can be triggered remotely by any master DNS server that has access to the slave server, making it an attractive target for attackers seeking to disrupt DNS infrastructure.
The flaw aligns with CWE-400, which addresses "Uncontrolled Resource Consumption" in software systems, specifically highlighting the lack of proper resource limits and validation during data processing operations. From an ATT&CK framework perspective, this vulnerability maps to techniques involving resource exhaustion and denial of service, specifically T1499.004 for "Endpoint Denial of Service" and T1595.001 for "Network Denial of Service" where the attack leverages the underlying DNS infrastructure to consume system resources. The vulnerability also relates to T1071.004 for "Application Layer Protocol: DNS" as it exploits the DNS protocol's zone transfer mechanism to carry out the attack. Organizations with DNS infrastructure relying on affected NSD versions face significant risk of service disruption and potential compromise of their network availability. The vulnerability demonstrates the importance of proper input validation and resource management in network services, particularly those handling potentially large data transfers like DNS zone transfers.
Mitigation strategies should prioritize immediate patching of affected NSD installations to version 4.1.11 or later, which includes proper resource limits and validation for zone transfer operations. Network administrators should also implement monitoring for unusual disk space consumption patterns in /tmp directories and establish automated alerts for rapid response to potential exploitation attempts. Additional defensive measures include implementing access controls to limit which master servers can initiate zone transfers, configuring proper disk space quotas for temporary directories, and establishing regular backup and recovery procedures to quickly restore services if exploitation occurs. The vulnerability underscores the critical importance of keeping DNS infrastructure software up to date and implementing proper resource management controls to prevent exploitation through resource exhaustion attacks.