CVE-2017-6303 in ytnef
Summary
by MITRE
An issue was discovered in ytnef before 1.9.1. This is related to a patch described as "6 of 9. Invalid Write and Integer Overflow."
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Analysis
by VulDB Data Team • 08/16/2020
The vulnerability identified as CVE-2017-6303 affects the ytnef library version 1.9.1 and earlier, representing a critical security flaw that emerged from an incomplete patch addressing previously known issues. This particular vulnerability stems from a specific set of problems labeled as "6 of 9. Invalid Write and Integer Overflow" within the library's codebase, indicating that the patch implementation itself introduced new exploitable conditions rather than resolving existing ones. The ytnef library serves as a tool for parsing TNEF (Transport Neutral Encapsulation Format) files commonly used in Microsoft Outlook email attachments, making it a potential attack vector through malicious email content.
The technical flaw manifests as an integer overflow condition combined with invalid write operations that occur during the processing of malformed TNEF data structures. When the library attempts to parse crafted input data, the integer overflow causes unexpected behavior in memory allocation and data handling routines, leading to memory corruption that can be exploited by attackers. This type of vulnerability falls under CWE-190, which specifically addresses integer overflow conditions, and CWE-787, which covers out-of-bounds write operations. The combination of these weaknesses creates a scenario where an attacker can manipulate input data to trigger buffer overflows and subsequent memory corruption that may allow for arbitrary code execution.
The operational impact of this vulnerability extends beyond simple denial of service, as it represents a potential path for remote code execution within applications that utilize the ytnef library for email attachment processing. Attackers could craft malicious TNEF attachments that, when processed by vulnerable applications, would trigger the integer overflow and invalid write conditions. This creates a significant risk for email servers, client applications, and any system that handles email attachments through the affected library. The vulnerability is particularly concerning because it affects a widely used library that may be integrated into numerous email processing systems, potentially creating a large attack surface across multiple organizations and applications.
Mitigation strategies for CVE-2017-6303 primarily focus on updating to ytnef version 1.9.1 or later, where the problematic patch has been properly implemented to address the integer overflow and invalid write conditions. Organizations should conduct thorough vulnerability assessments to identify all systems that utilize the affected library and ensure comprehensive patch management protocols are in place. Additional protective measures include implementing email filtering rules that block suspicious TNEF attachments, deploying sandboxing mechanisms for email attachment processing, and establishing network monitoring to detect potential exploitation attempts. From an ATT&CK framework perspective, this vulnerability maps to techniques involving execution through email attachments and privilege escalation through memory corruption, making it a significant concern for email security and endpoint protection strategies.