CVE-2017-6802 in ytnef
Summary
by MITRE
An issue was discovered in ytnef before 1.9.2. There is a potential heap-based buffer over-read on incoming Compressed RTF Streams, related to DecompressRTF() in libytnef.
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Analysis
by VulDB Data Team • 09/05/2020
The vulnerability identified as CVE-2017-6802 represents a critical heap-based buffer over-read condition affecting the ytnef library version 1.9.1 and earlier. This issue specifically manifests when processing incoming Compressed RTF Streams through the DecompressRTF() function within the library's codebase. The ytnef library serves as a tool for extracting data from TNEF (Transport Neutral Encapsulation Format) files commonly used in Microsoft Outlook email messages, making this vulnerability particularly concerning for email security systems and email processing applications.
The technical flaw stems from inadequate input validation and memory management within the DecompressRTF() function which handles decompression of RTF streams. When the library encounters malformed or specially crafted compressed RTF data, it fails to properly bounds-check memory allocations during the decompression process. This allows an attacker to potentially read data from memory locations beyond the allocated buffer boundaries, resulting in information disclosure and potential system instability. The vulnerability classifies as a heap-based buffer over-read according to CWE-125, which occurs when a program reads from memory beyond the end of a heap-allocated buffer.
The operational impact of this vulnerability extends beyond simple information disclosure, as it could enable attackers to extract sensitive data from memory segments that may contain authentication tokens, cryptographic keys, or other confidential information. Email servers, security scanning appliances, and any system processing untrusted TNEF files through the affected ytnef library become potential targets. The vulnerability could be exploited through crafted email attachments or malicious TNEF data streams, making it particularly dangerous in email security contexts where automated processing of incoming messages is common. This aligns with ATT&CK technique T1059.007 for execution through email attachments and T1566 for spearphishing attacks.
Mitigation strategies should focus on immediate library updates to version 1.9.2 or later where the buffer over-read issue has been addressed through proper bounds checking and memory management. Organizations should also implement additional input validation measures for email processing systems, including sandboxed environments for TNEF file analysis and network segmentation to limit potential attack vectors. Regular security assessments of email processing infrastructure and monitoring for anomalous memory access patterns can help detect exploitation attempts. The vulnerability demonstrates the critical importance of proper memory management in security-sensitive libraries and highlights the need for comprehensive testing of input validation mechanisms in file processing applications.