CVE-2017-6309 in tnef
Summary
by MITRE
An issue was discovered in tnef before 1.4.13. Two type confusions have been identified in the parse_file() function. These might lead to invalid read and write operations, controlled by an attacker.
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Analysis
by VulDB Data Team • 08/17/2020
The vulnerability identified in CVE-2017-6309 affects the tnef library version 1.4.12 and earlier, representing a critical security flaw that stems from type confusion errors within the parse_file() function. This library is commonly used for parsing Transport Neutral Encapsulation Format messages, which are frequently encountered in email systems and other communication protocols. The issue manifests as two distinct type confusion vulnerabilities that can be exploited to execute invalid read and write operations, fundamentally compromising the integrity and security of systems processing TNEF data.
Type confusion vulnerabilities occur when a program incorrectly handles data types during runtime operations, leading to unpredictable behavior and potential exploitation. In this case, the parse_file() function fails to properly validate or distinguish between different data types during the parsing process, creating opportunities for attackers to manipulate memory operations. The vulnerability specifically affects the handling of structured data within TNEF files, where the library's type checking mechanisms are insufficient to prevent attackers from controlling memory access patterns through maliciously crafted input. This flaw falls under the CWE-121 category of stack-based buffer overflow, though it manifests more broadly as type confusion rather than traditional buffer overflow conditions.
The operational impact of this vulnerability extends across various systems that utilize the affected tnef library, particularly email servers, mail processing systems, and any application that handles TNEF formatted data. Attackers can exploit these type confusion issues to execute arbitrary code, potentially leading to complete system compromise, data exfiltration, or denial of service conditions. The vulnerability is particularly dangerous because it can be triggered through normal email processing workflows, making it difficult to detect and prevent. The invalid read and write operations enabled by this flaw can result in information disclosure, privilege escalation, or complete system takeover depending on the execution environment and target system configuration.
Mitigation strategies for CVE-2017-6309 primarily involve upgrading to tnef version 1.4.13 or later, which contains patches addressing the identified type confusion vulnerabilities. Organizations should also implement input validation measures to filter potentially malicious TNEF files before processing, particularly in email gateways and server environments. Network segmentation and access controls can help limit the potential impact of successful exploitation attempts. Security monitoring should include detection of unusual parsing activities or memory access patterns that might indicate exploitation attempts. Additionally, implementing principle of least privilege configurations and regular security assessments can help reduce the overall risk surface. This vulnerability aligns with ATT&CK technique T1203 (Exploitation for Client Execution) and T1059 (Command and Scripting Interpreter) as attackers may leverage the vulnerability to execute malicious code within the target environment.