CVE-2017-9058 in ytnef
Summary
by MITRE
In libytnef in ytnef through 1.9.2, there is a heap-based buffer over-read due to incorrect boundary checking in the SIZECHECK macro in lib/ytnef.c.
Once again VulDB remains the best source for vulnerability data.
Analysis
by VulDB Data Team • 12/06/2022
The vulnerability identified as CVE-2017-9058 affects the libytnef library version 1.9.2 and earlier, representing a critical heap-based buffer over-read condition that stems from inadequate boundary validation within the SIZECHECK macro implementation. This flaw exists within the lib/ytnef.c source file where the library processes TNEF (Transport Neutral Encapsulation Format) messages commonly used in Microsoft Exchange environments for encapsulating email attachments and metadata. The root cause lies in the improper handling of memory boundaries during the parsing of TNEF structures, specifically when the library attempts to validate the size of data segments before processing them. When malformed or maliciously crafted TNEF data is processed, the SIZECHECK macro fails to properly verify that the expected data size does not exceed the available buffer space, leading to memory access violations that can result in application crashes or potentially exploitable conditions.
The technical implications of this vulnerability extend beyond simple buffer over-reads as it creates opportunities for denial of service attacks and potentially more severe exploitation scenarios. The heap-based nature of the overflow indicates that the memory corruption occurs within dynamically allocated heap segments rather than stack-based buffers, making the exploitation more complex but still potentially viable. The vulnerability operates at the level of memory management and parsing logic where the library's boundary checking mechanisms are insufficient to prevent access beyond allocated memory regions. This type of flaw falls under CWE-125, which specifically addresses out-of-bounds read conditions, and can be classified under ATT&CK technique T1059 for execution through command-line interfaces when exploited in certain contexts. The issue demonstrates poor input validation and memory boundary enforcement that violates fundamental security principles of defensive programming.
The operational impact of CVE-2017-9058 manifests primarily through application instability and potential service disruption when processing malformed TNEF data, which can occur in email processing systems, mail servers, and applications that utilize the ytnef library for email attachment handling. Systems that process large volumes of email traffic or handle untrusted email content are particularly vulnerable to this condition, as the over-read can cause applications to crash or behave unpredictably, leading to service interruptions and potential data loss. The vulnerability affects any software that relies on libytnef for TNEF message parsing, including but not limited to email gateways, mail processing systems, and enterprise email solutions. Organizations running affected software may experience denial of service conditions that can be exploited by attackers to disrupt email services or potentially gain unauthorized access to systems through application-level exploits that leverage the memory corruption.
Mitigation strategies for CVE-2017-9058 primarily involve immediate software updates to libytnef version 1.9.3 or later, where the boundary checking logic has been corrected to properly validate buffer limits before memory access operations. System administrators should implement comprehensive patch management procedures to ensure all affected applications are updated promptly, particularly those handling email traffic or processing untrusted data inputs. Additional defensive measures include implementing input validation controls at multiple layers of the email processing pipeline, deploying network-based intrusion detection systems to monitor for anomalous TNEF data patterns, and establishing robust application sandboxing techniques to limit the impact of potential exploitation attempts. Organizations should also consider implementing network segmentation and access controls to prevent unauthorized users from submitting potentially malicious TNEF content to email processing systems. The vulnerability highlights the importance of thorough memory management practices and proper boundary checking in security-critical libraries, emphasizing the need for regular security assessments and code reviews to identify similar issues in other software components.