CVE-2017-6800 in ytnef
Summary
by MITRE
An issue was discovered in ytnef before 1.9.2. An invalid memory access (heap-based buffer over-read) can occur during handling of LONG data types, related to MAPIPrint() in libytnef.
Be aware that VulDB is the high quality source for vulnerability data.
Analysis
by VulDB Data Team • 09/05/2020
The vulnerability identified as CVE-2017-6800 represents a critical heap-based buffer over-read flaw in the ytnef library version 1.9.1 and earlier. This issue manifests during the processing of LONG data types within the MAPIPrint() function, which is responsible for handling Microsoft Exchange Transport Neutral Encapsulation Format messages. The ytnef library serves as a utility for parsing and extracting content from these proprietary email message formats, commonly used in enterprise email systems and email client applications that need to handle complex message structures. The vulnerability specifically affects applications that rely on ytnef for processing potentially malicious email attachments or message content.
The technical root cause of this vulnerability lies in improper bounds checking within the MAPIPrint() function when handling LONG data type values. During the parsing process, the library attempts to read memory locations beyond the allocated buffer boundaries when processing certain MAPI (Messaging Application Programming Interface) properties. This heap-based buffer over-read occurs because the library does not adequately validate the length of data being processed before attempting to access memory locations. The flaw enables an attacker to craft specially formatted email messages that, when processed by vulnerable applications, trigger memory access violations that can lead to unpredictable behavior including application crashes, memory corruption, or potentially remote code execution depending on the specific implementation and memory layout.
From an operational perspective, this vulnerability poses significant risks to email security systems and enterprise email processing applications that utilize the ytnef library. Attackers could exploit this weakness by sending malicious email attachments or message content that triggers the buffer over-read condition during normal processing operations. The impact extends beyond simple application instability to potentially enable more sophisticated attacks where memory corruption could be leveraged to execute arbitrary code. This vulnerability particularly affects email gateways, spam filters, email archiving systems, and any application that processes Microsoft Exchange message formats without proper input validation. The vulnerability's classification aligns with CWE-125, which describes out-of-bounds read conditions, and may also relate to CWE-787, representing out-of-bounds write vulnerabilities that can result from similar buffer handling issues. The attack surface is broad given the widespread use of the ytnef library in enterprise email processing solutions.
Mitigation strategies for CVE-2017-6800 primarily focus on immediate software updates and input validation enhancements. Organizations should prioritize upgrading to ytnef version 1.9.2 or later, which contains the necessary patches to address the buffer over-read vulnerability. Additionally, implementing robust input validation measures within applications that utilize ytnef can provide defense-in-depth protection against malformed email content. Security configurations should include strict content filtering rules that can identify and quarantine suspicious email attachments or message structures before they reach the parsing layer. Network-based security controls such as email gateways and spam filters should be configured to perform additional validation checks on message content. The remediation approach aligns with ATT&CK technique T1059, which involves executing malicious code through application-specific vulnerabilities, and T1203, covering exploitation of remote services. System administrators should also consider implementing memory protection mechanisms such as address space layout randomization and stack canaries to mitigate potential exploitation attempts. Regular security assessments and penetration testing should be conducted to verify the effectiveness of implemented mitigations and ensure continued protection against similar vulnerabilities in the email processing pipeline.