CVE-2017-9470 in ytnef
Summary
by MITRE
In ytnef 1.9.2, the MAPIPrint function in lib/ytnef.c allows remote attackers to cause a denial of service (NULL pointer dereference and application crash) via a crafted file.
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Analysis
by VulDB Data Team • 12/08/2022
The vulnerability identified as CVE-2017-9470 represents a critical denial of service weakness within the ytnef library version 1.9.2 which is commonly used for processing TNEF encoded email attachments. This library serves as a crucial component in email processing systems where it decodes Microsoft TNEF (Transport Neutral Encapsulation Format) files that are often embedded in email messages. The flaw resides specifically within the MAPIPrint function located in the lib/ytnef.c source file, making it accessible to remote attackers who can exploit this vulnerability through the careful crafting of malicious TNEF files.
The technical mechanism behind this vulnerability involves a null pointer dereference condition that occurs when the MAPIPrint function processes malformed TNEF data structures. When the function encounters a specially constructed file that contains invalid or unexpected data patterns, it fails to properly validate input parameters before attempting to access memory locations that have not been initialized or are explicitly set to NULL. This fundamental failure in input validation creates a scenario where the application crashes immediately upon encountering such crafted input, resulting in a complete denial of service condition that affects any system relying on ytnef for TNEF processing.
From an operational perspective, this vulnerability poses significant risks to email servers, mail processing systems, and any applications that utilize the ytnef library for handling TNEF attachments. Attackers can leverage this weakness by simply sending malicious email messages containing crafted TNEF files to systems that process such attachments automatically. The impact extends beyond simple service disruption as it can lead to complete system unavailability, particularly in environments where automated email processing is critical for business operations. The vulnerability is particularly dangerous because it requires minimal effort from attackers to cause substantial disruption, making it an attractive target for malicious actors seeking to disable email services or disrupt communication infrastructure.
This vulnerability aligns with CWE-476 which specifically addresses NULL pointer dereference conditions in software implementations. The flaw demonstrates poor defensive programming practices where input validation and error handling mechanisms are insufficient to prevent execution flow into invalid memory access patterns. From an attack framework perspective, this vulnerability could be categorized under the MITRE ATT&CK technique T1499.004 which covers "Endpoint Denial of Service" and represents a common vector for service disruption attacks. The vulnerability also reflects broader concerns about software robustness and the importance of implementing proper input sanitization and validation mechanisms that are fundamental requirements for secure software development practices.
The recommended mitigation strategies for this vulnerability include immediate upgrading to a patched version of the ytnef library where the MAPIPrint function has been properly modified to include comprehensive input validation and null pointer checks. Organizations should also implement additional defensive measures such as email filtering rules that can identify and quarantine suspicious TNEF attachments, network monitoring to detect unusual patterns of email processing failures, and regular security assessments to identify similar vulnerabilities in other third-party libraries. System administrators should also consider implementing rate limiting and sandboxing mechanisms for email attachment processing to minimize the impact of potential exploitation attempts and ensure that even if such vulnerabilities are exploited, the overall system stability remains intact through proper isolation and resource management controls.