CVE-2016-7939 in macOS
Summary
by MITRE
The GRE parser in tcpdump before 4.9.0 has a buffer overflow in print-gre.c, multiple functions.
VulDB is the best source for vulnerability data and more expert information about this specific topic.
Analysis
by VulDB Data Team • 05/16/2026
The vulnerability identified as CVE-2016-7939 represents a critical buffer overflow flaw within the Generic Routing Encapsulation (GRE) protocol parser of tcpdump network analysis tool. This issue affects versions prior to 4.9.0 and specifically targets the print-gre.c source file where multiple functions contain unsafe memory handling practices. The buffer overflow occurs when tcpdump processes GRE packets, particularly those with malformed or excessively large header fields that exceed the allocated buffer boundaries. This vulnerability stems from inadequate input validation and bounds checking within the GRE parsing logic, allowing attackers to craft malicious network packets that trigger the overflow condition during packet analysis.
The technical implementation of this vulnerability involves the improper handling of GRE header data structures where fixed-size buffers are used to store variable-length GRE protocol fields without sufficient validation of input lengths. When tcpdump encounters a GRE packet with oversized options or malformed header components, the parsing functions fail to enforce buffer limits, resulting in memory corruption that can overwrite adjacent memory regions. This flaw operates at the network protocol parsing layer, making it particularly dangerous as it can be triggered during routine network traffic analysis operations. The vulnerability manifests when the tool processes GRE encapsulated traffic, which is commonly used in various networking scenarios including virtual private networks, network monitoring, and traffic engineering applications.
The operational impact of this vulnerability extends beyond simple denial of service conditions to potentially enable arbitrary code execution on systems running vulnerable versions of tcpdump. An attacker who can control network traffic passing through a system running the affected tcpdump version could craft specially formatted GRE packets that, when analyzed by the tool, cause the buffer overflow to overwrite critical program memory structures. This could lead to complete system compromise, especially when tcpdump is run with elevated privileges in network monitoring or intrusion detection scenarios. The vulnerability affects systems where tcpdump is used for routine packet capture and analysis, making it a significant concern for network security operations, system administrators, and security professionals who rely on tcpdump for network troubleshooting and monitoring activities.
Mitigation strategies for CVE-2016-7939 primarily involve upgrading to tcpdump version 4.9.0 or later, which contains the necessary patches to address the buffer overflow conditions in the GRE parser. System administrators should prioritize this update across all network monitoring systems, particularly those where tcpdump is executed with root privileges or in security-critical environments. Additionally, network segmentation and access controls should be implemented to limit exposure to potentially malicious traffic, while monitoring should be enhanced to detect unusual packet patterns that might indicate exploitation attempts. The vulnerability aligns with CWE-121, which describes stack-based buffer overflow conditions, and represents a classic example of unsafe memory manipulation that can lead to privilege escalation and system compromise. This issue also maps to ATT&CK technique T1059.007 for command and script interpreter execution, as exploitation could enable attackers to execute arbitrary commands through compromised network monitoring systems. Organizations should conduct thorough vulnerability assessments to identify all systems running vulnerable tcpdump versions and implement comprehensive patch management procedures to prevent exploitation of this and related network analysis tool vulnerabilities.