CVE-2017-9146 in ytnef
Summary
by MITRE
The TNEFFillMapi function in lib/ytnef.c in libytnef in ytnef through 1.9.2 does not ensure a nonzero count value before a certain memory allocation, which allows remote attackers to cause a denial of service (heap-based buffer overflow and application crash) or possibly have unspecified other impact via a crafted tnef file.
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Analysis
by VulDB Data Team • 12/07/2022
The vulnerability identified as CVE-2017-9146 resides within the TNEFFillMapi function in libytnef library version 1.9.2 and earlier, representing a critical memory safety issue that affects applications processing TNEF (Transport Neutral Encapsulation Format) files. This flaw manifests in the ytnef library's handling of malformed TNEF data structures, specifically when processing the MAPI (Messaging Application Programming Interface) properties within these files. The vulnerability stems from insufficient validation of input parameters before memory allocation operations, creating a scenario where attacker-controlled data can manipulate the allocation process and lead to unpredictable system behavior. The TNEF format is commonly used in Microsoft Exchange environments to encapsulate email messages and their attachments, making this vulnerability particularly concerning for email processing systems and security applications that handle such data.
The technical exploitation of this vulnerability occurs when the TNEFFillMapi function processes a crafted TNEF file containing malformed MAPI property count values. The function fails to validate that the count parameter is nonzero before proceeding with memory allocation, allowing attackers to specify zero or negative values that result in invalid memory operations. When the application attempts to allocate memory based on these invalid count values, it triggers heap-based buffer overflows that can corrupt adjacent memory regions and cause application crashes. This memory corruption can potentially be leveraged to execute arbitrary code or escalate privileges, depending on the specific application environment and memory layout. The vulnerability's impact extends beyond simple denial of service as it may enable more sophisticated attacks when combined with other exploitation techniques, particularly in systems where memory corruption can be controlled to redirect program execution flow.
From an operational standpoint, this vulnerability affects any system that utilizes the libytnef library for processing TNEF files, including email servers, security scanning tools, and document processing applications. The remote attack vector means that malicious actors can exploit this vulnerability through email attachments or file uploads without requiring local access to the target system. The potential for unspecified other impacts suggests that beyond immediate application crashes, this vulnerability could enable privilege escalation or information disclosure depending on the execution environment. Security professionals should consider this vulnerability in the context of email security systems where TNEF files are commonly processed, as these systems represent prime targets for exploitation due to their exposure to external email traffic. The vulnerability's classification aligns with CWE-129, which addresses insufficient validation of length parameters, and can be mapped to ATT&CK technique T1059 for command and scripting interpreter usage in exploitation scenarios.
Organizations should prioritize immediate patching of all systems running ytnef versions 1.9.2 or earlier, as the vulnerability represents a significant risk to system availability and potentially security. Mitigation strategies include implementing strict input validation for TNEF file processing, deploying network-based intrusion detection systems to monitor for suspicious TNEF file patterns, and establishing robust application sandboxing to limit the impact of potential exploitation. Security teams should also consider implementing email filtering rules that block or quarantine TNEF attachments from untrusted sources, as these files are often used in spear-phishing campaigns. Additionally, regular security assessments of systems processing TNEF data should include specific testing for this vulnerability, with particular attention to how applications handle malformed input data and memory allocation operations. The vulnerability serves as a reminder of the critical importance of input validation and memory safety practices in security-critical applications, particularly those handling untrusted data from external sources.