CVE-2017-9471 in ytnef
Summary
by MITRE
In ytnef 1.9.2, the SwapWord function in lib/ytnef.c allows remote attackers to cause a denial of service (heap-based buffer over-read and application crash) via a crafted file.
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Analysis
by VulDB Data Team • 12/08/2022
The vulnerability identified as CVE-2017-9471 represents a critical heap-based buffer over-read flaw within the ytnef library version 1.9.2. This library serves as a tool for decoding Microsoft TNEF (Transport Neutral Encapsulation Format) files, which are commonly used in email systems to encapsulate rich text and embedded objects. The flaw specifically resides in the SwapWord function located within the lib/ytnef.c source file, making it accessible to remote attackers who can manipulate the input data to trigger the vulnerability. The affected function processes word-sized data elements and fails to properly validate the boundaries of memory allocations, creating a condition where maliciously crafted input can cause the application to read beyond allocated heap memory regions.
The technical nature of this vulnerability aligns with CWE-125, which describes out-of-bounds read conditions where a program accesses memory beyond the boundaries of a valid buffer. This particular implementation flaw occurs when the SwapWord function handles data structures that do not conform to expected size parameters, causing the program to traverse into adjacent memory locations that may contain arbitrary data or be unmapped. The buffer over-read condition manifests as an application crash, resulting in a denial of service that prevents legitimate users from accessing the affected service or application that relies on ytnef for TNEF file processing. Attackers can exploit this vulnerability by crafting specially formatted TNEF files that, when processed by applications using the vulnerable library, will trigger the heap corruption and subsequent crash.
The operational impact of CVE-2017-9471 extends beyond simple service disruption, as it can be leveraged in broader attack scenarios within email processing systems, file transfer applications, and any software that utilizes ytnef for handling Microsoft TNEF encapsulated content. This vulnerability particularly affects email servers, spam filters, and document processing systems that may automatically process TNEF attachments without proper input validation. The remote exploitation capability means that attackers can trigger the vulnerability from outside the target network, making it a significant concern for organizations that process email traffic or handle file transfers from untrusted sources. Security professionals should consider this vulnerability in relation to ATT&CK technique T1204.002, which involves exploitation of remote services through malicious file attachments, potentially leading to more sophisticated attacks if the initial denial of service is followed by additional exploitation attempts.
Mitigation strategies for CVE-2017-9471 should prioritize immediate remediation through library updates to versions that address the buffer over-read condition in the SwapWord function. Organizations should implement input validation measures that verify the integrity of TNEF file structures before processing, including bounds checking and size validation of expected data elements. Network-level defenses such as email filtering rules and attachment scanning systems can provide additional protection by identifying and quarantining suspicious TNEF files before they reach vulnerable applications. Security teams should also consider implementing application sandboxing techniques that isolate TNEF processing components to limit the potential impact of successful exploitation attempts. The vulnerability demonstrates the importance of proper memory management practices and input validation in preventing heap-based buffer overflows, aligning with industry best practices for secure coding and vulnerability remediation as outlined in various cybersecurity frameworks and standards.