CVE-2017-6300 in ytnef
Summary
by MITRE
An issue was discovered in ytnef before 1.9.1. This is related to a patch described as "3 of 9. Buffer Overflow in version field in lib/tnef-types.h."
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Analysis
by VulDB Data Team • 08/16/2020
The vulnerability identified as CVE-2017-6300 represents a critical buffer overflow flaw within the ytnef library version 1.9.0 and earlier. This issue specifically targets the version field handling mechanism located in the lib/tnef-types.h file, which is a core component of the library responsible for processing TNEF (Transport Neutral Encapsulation Format) data. The TNEF format is commonly used by Microsoft Outlook to encapsulate rich text messages and attachments, making this vulnerability particularly concerning for email processing systems. The flaw manifests when the library attempts to parse and handle version information within TNEF messages, creating an exploitable condition that can be leveraged by attackers to execute arbitrary code or cause system crashes.
This buffer overflow vulnerability falls under the CWE-121 category of stack-based buffer overflow, where insufficient bounds checking allows an attacker to write data beyond the allocated buffer space. The specific nature of this flaw in the version field processing means that when maliciously crafted TNEF messages are processed, the library fails to properly validate the length of version data before copying it into a fixed-size buffer. The vulnerability is classified as a CWE-787 Out-of-bounds Write, which is a direct consequence of inadequate input validation and memory management practices. Attackers can exploit this weakness by crafting specially formatted TNEF messages that contain oversized version fields, leading to memory corruption that can be leveraged for privilege escalation or denial of service attacks.
The operational impact of this vulnerability extends across various systems that rely on ytnef for email processing, particularly those handling untrusted email content from external sources. Email servers, spam filters, and content inspection systems that utilize this library become vulnerable to exploitation, creating potential entry points for attackers seeking to compromise network infrastructure. The vulnerability affects not only individual email clients but also enterprise email processing pipelines where automated systems parse large volumes of incoming messages. From an adversarial perspective, this flaw aligns with ATT&CK technique T1203 Exploitation for Client Execution, as attackers can leverage the buffer overflow to execute malicious code within the context of applications using ytnef. The vulnerability's exploitation potential is further amplified because TNEF processing occurs during normal email handling operations, making detection and prevention more challenging.
Mitigation strategies for CVE-2017-6300 require immediate patching of the ytnef library to version 1.9.1 or later, which contains the necessary fixes for the buffer overflow condition. Organizations should implement comprehensive vulnerability management processes to ensure all instances of the library are updated across their infrastructure. Additional protective measures include implementing email filtering rules that identify and quarantine suspicious TNEF attachments, deploying network-based intrusion detection systems to monitor for exploitation attempts, and conducting regular security assessments of email processing systems. The fix implemented in version 1.9.1 addresses the root cause by introducing proper bounds checking and input validation for version field data, preventing the buffer overflow condition from occurring. Security teams should also consider implementing application sandboxing or containerization for email processing applications to limit the potential impact if exploitation occurs, and establish monitoring procedures to detect unusual patterns in email processing that might indicate exploitation attempts.