CVE-2017-12995 in macOS
Summary
by MITRE
The DNS parser in tcpdump before 4.9.2 could enter an infinite loop due to a bug in print-domain.c:ns_print().
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Analysis
by VulDB Data Team • 12/05/2025
The vulnerability identified as CVE-2017-12995 represents a critical denial of service flaw within tcpdump's DNS parsing functionality. This issue affects versions prior to 4.9.2 and stems from a specific implementation error in the print-domain.c file, particularly within the ns_print() function. The flaw demonstrates how seemingly minor code defects in network protocol analysis tools can lead to significant operational disruptions. When tcpdump encounters certain malformed DNS responses during packet capture operations, the parser becomes trapped in an infinite loop, consuming excessive CPU resources and rendering the tool unusable for network monitoring purposes. This behavior directly impacts network security operations and incident response activities that rely on tcpdump for packet analysis and troubleshooting.
The technical root cause of this vulnerability lies in improper handling of DNS domain name compression during the ns_print() function execution. DNS protocol utilizes a compression mechanism where domain names can reference previously seen labels through pointers, allowing for more efficient packet transmission. However, the tcpdump implementation fails to properly validate these compression pointers, leading to situations where the parser follows circular references or malformed pointer chains. This creates an infinite loop condition where the parser continuously processes the same domain name segments without proper termination conditions. The flaw aligns with CWE-835, which specifically addresses infinite loops in software implementations, and demonstrates how improper pointer handling can lead to resource exhaustion attacks.
The operational impact of this vulnerability extends beyond simple denial of service conditions, affecting critical network security infrastructure and monitoring capabilities. Organizations relying on tcpdump for network traffic analysis, intrusion detection, and security auditing face potential operational outages when encountering malicious or malformed DNS traffic. Attackers could exploit this vulnerability by crafting specially crafted DNS responses that trigger the infinite loop, effectively disabling network monitoring tools without requiring authentication or elevated privileges. This makes the vulnerability particularly dangerous in environments where tcpdump is used for continuous network surveillance, as it could go unnoticed until the system becomes unresponsive. The attack surface includes any network monitoring system that processes DNS traffic through tcpdump, encompassing security operations centers, network troubleshooting environments, and automated monitoring solutions.
Mitigation strategies for CVE-2017-12995 primarily focus on immediate software updates and deployment of patched versions. Organizations should prioritize upgrading to tcpdump version 4.9.2 or later, which contains the necessary fixes for the ns_print() function implementation. Additionally, network administrators should implement defensive measures such as rate limiting for DNS traffic analysis and monitoring for unusual CPU usage patterns that might indicate exploitation attempts. The vulnerability also highlights the importance of input validation in network protocol parsers, aligning with ATT&CK technique T1071.004 for application layer protocol manipulation. Security teams should consider implementing network segmentation and access controls to limit exposure, while also establishing monitoring procedures to detect and respond to potential exploitation attempts. Regular vulnerability assessments and penetration testing should include verification of tcpdump installations to ensure proper patch levels and prevent unauthorized exploitation of this denial of service vulnerability.