CVE-2017-12988 in macOS
Summary
by MITRE
The telnet parser in tcpdump before 4.9.2 has a buffer over-read in print-telnet.c:telnet_parse().
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Analysis
by VulDB Data Team • 09/06/2024
The vulnerability identified as CVE-2017-12988 represents a critical buffer over-read flaw within the telnet protocol parser of tcpdump version 4.9.1 and earlier. This issue specifically manifests in the print-telnet.c source file at the telnet_parse() function, where improper input validation leads to memory access violations that can be exploited by malicious actors. The vulnerability stems from inadequate bounds checking when processing telnet protocol data streams, allowing an attacker to craft specially malformed telnet packets that trigger memory corruption during packet analysis. The affected tcpdump version represents a widely deployed network traffic analysis tool used by security professionals, network administrators, and forensic analysts for monitoring and troubleshooting network communications. When exploited, this vulnerability can result in application crashes, denial of service conditions, and potentially arbitrary code execution depending on the system configuration and memory layout. The flaw directly relates to CWE-125, which describes out-of-bounds read vulnerabilities where programs access memory locations beyond the intended buffer boundaries. This vulnerability falls under the ATT&CK technique T1046, as it can be leveraged to perform network service discovery and reconnaissance activities by manipulating network traffic analysis tools. The impact extends beyond simple service disruption since tcpdump is commonly used in security monitoring environments where its reliability is paramount for network traffic inspection and incident response activities.
The technical implementation of this buffer over-read occurs when tcpdump processes telnet protocol negotiations and options within network packets. The telnet_parse() function fails to properly validate the length of incoming telnet option data before attempting to read from the buffer, creating a scenario where attacker-controlled data can cause the parser to access memory locations beyond the allocated buffer boundaries. This memory corruption can lead to unpredictable behavior including application crashes, data corruption, or in some cases, potential code execution if the memory corruption affects critical program structures. The vulnerability is particularly concerning because telnet remains in use within legacy systems and network infrastructure, making it a viable attack vector for adversaries seeking to compromise network monitoring tools. Network administrators who rely on tcpdump for security monitoring and incident response may find their tools rendered ineffective or potentially compromised by this vulnerability. The flaw demonstrates a classic buffer management issue where the parser does not account for variable-length telnet options that can exceed expected buffer sizes during protocol negotiation phases. Attackers can exploit this by crafting malicious telnet packets that contain oversized option data, triggering the over-read condition during packet processing. The vulnerability's exploitation requires minimal network access and can be executed through standard network traffic injection techniques.
Mitigation strategies for CVE-2017-12988 involve immediate patching of tcpdump installations to version 4.9.2 or later, which contains the necessary buffer validation fixes. Organizations should prioritize updating their tcpdump deployments across all network monitoring systems, security appliances, and forensic analysis platforms that may be vulnerable. System administrators should implement network segmentation and access controls to limit exposure of tcpdump instances to untrusted network traffic sources. Additional defensive measures include configuring tcpdump to operate with restricted privileges and implementing monitoring for abnormal tcpdump behavior or crash patterns. The vulnerability highlights the importance of proper input validation and bounds checking in network protocol parsers, particularly those handling variable-length data structures common in application layer protocols. Security teams should conduct inventory assessments to identify all systems running vulnerable tcpdump versions and ensure comprehensive patch management processes are in place. Organizations may also consider implementing alternative network analysis tools or deploying intrusion detection systems that can detect and block malformed telnet traffic patterns. The fix implemented in tcpdump 4.9.2 demonstrates proper buffer handling techniques that validate input lengths before memory access operations, preventing the over-read condition that enabled exploitation. Regular security assessments of network monitoring tools should be conducted to identify similar vulnerabilities in other protocol parsers and ensure that defensive coding practices are consistently applied throughout network security infrastructure components.