CVE-2017-12142 in ytnef
Summary
by MITRE
In ytnef 1.9.2, an invalid memory read vulnerability was found in the function SwapDWord in ytnef.c, which allows attackers to cause a denial of service via a crafted file.
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Analysis
by VulDB Data Team • 12/14/2022
The vulnerability identified as CVE-2017-12142 represents a critical memory access flaw within the ytnef library version 1.9.2, which is widely used for parsing TNEF (Transport Neutral Encapsulation Format) files commonly found in Microsoft Outlook messages. This library serves as a crucial component in email processing systems, particularly in environments where email archiving, filtering, or content extraction is performed. The flaw exists within the SwapDWord function in the ytnef.c source file, which is responsible for handling byte order conversions during TNEF data parsing operations. The vulnerability manifests when the library processes malformed or specially crafted TNEF files that contain invalid memory references, leading to unpredictable behavior and system instability.
The technical nature of this vulnerability aligns with CWE-125, which describes out-of-bounds read conditions where programs access memory locations beyond the intended buffer boundaries. When an attacker crafts a malicious TNEF file with malformed data structures, the SwapDWord function attempts to read memory locations that are either uninitialized, unallocated, or otherwise invalid. This invalid memory read operation triggers a segmentation fault or access violation, causing the application utilizing ytnef to crash or terminate unexpectedly. The vulnerability is particularly concerning because it operates at the parsing layer, meaning any application that relies on ytnef for TNEF file processing becomes susceptible to denial of service attacks. The flaw demonstrates poor input validation practices and inadequate bounds checking within the memory access routines.
From an operational perspective, this vulnerability creates significant risk for organizations that process large volumes of email traffic or maintain email archiving systems. Attackers can exploit this weakness by sending specially crafted TNEF attachments that, when processed by vulnerable applications, result in service disruption and potential system downtime. The denial of service impact extends beyond individual applications to entire email processing pipelines, potentially affecting business continuity and communication services. The vulnerability is particularly dangerous in automated email filtering systems, spam detection engines, and archiving solutions where the ytnef library is integrated into the core processing workflow. Security teams must consider that this vulnerability can be leveraged as part of broader attack campaigns targeting email infrastructure, potentially disrupting critical communication channels.
The mitigation strategy for CVE-2017-12142 requires immediate application of the vendor-provided patch or upgrade to ytnef version 1.9.3, which contains the necessary fixes for the invalid memory read issue. Organizations should implement defensive measures including input validation for TNEF files, sandboxing email processing components, and deploying intrusion detection systems that can identify and block suspicious TNEF attachments. Network administrators should consider implementing email filtering rules that quarantine or reject TNEF files entirely if they cannot be processed securely. The vulnerability also highlights the importance of proper memory management practices and input validation, aligning with ATT&CK technique T1059.007 for execution through scripting and T1499.004 for network disruption attacks. Regular security assessments of third-party libraries and dependencies should be conducted to identify similar vulnerabilities in other components of email processing infrastructure, as this flaw demonstrates how seemingly minor parsing issues can create significant operational risks.