CVE-2017-6307 in tnef
Summary
by MITRE
An issue was discovered in tnef before 1.4.13. Two OOB Writes have been identified in src/mapi_attr.c:mapi_attr_read(). 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-2017-6307 affects the TNEF (Transport Neutral Encapsulation Format) library version 1.4.12 and earlier, representing a critical security flaw that can be exploited to execute arbitrary code or cause system instability. This issue manifests as two out-of-bounds write operations within the mapi_attr_read() function located in src/mapi_attr.c, which processes Microsoft's MAPI attributes during TNEF file parsing. The vulnerability arises when the library processes malformed TNEF files containing crafted payload data that manipulates the expected data structures, leading to memory corruption that can be leveraged by attackers for remote code execution or denial of service attacks.
The technical flaw stems from insufficient input validation and bounds checking within the TNEF parsing routine, specifically in how the library handles attribute length specifications and data buffer allocation. When processing TNEF messages, the mapi_attr_read() function fails to properly validate the size parameters of MAPI attributes before attempting to write data into allocated memory buffers. This lack of proper boundary checking creates opportunities for attackers to craft malicious TNEF files that contain oversized attribute values or malformed length fields, causing the application to write data beyond the intended memory boundaries. The vulnerability is categorized under CWE-129 as an insufficient validation of length of buffer, and more specifically aligns with CWE-787 for out-of-bounds write conditions that can lead to memory corruption and potential code execution.
The operational impact of this vulnerability extends beyond simple denial of service scenarios, as it can be exploited in various attack vectors including email-based attacks, file attachment exploitation, and potentially network-based compromise scenarios. Attackers can leverage this vulnerability by crafting specially formatted TNEF files that, when processed by vulnerable applications, trigger the out-of-bounds write conditions. The memory corruption can result in application crashes, data corruption, or more critically, provide attackers with opportunities to execute arbitrary code with the privileges of the affected application. This vulnerability is particularly concerning in environments where TNEF files are processed automatically, such as email servers, document management systems, or any application that handles Microsoft Exchange format messages. The attack surface is broadened by the fact that TNEF is commonly used in Microsoft Exchange environments and can be embedded within various email formats, making it a significant concern for enterprise security.
Mitigation strategies for CVE-2017-6307 primarily involve upgrading to TNEF library version 1.4.13 or later, which includes proper bounds checking and input validation fixes. Organizations should also implement defensive measures such as email filtering policies that scan for and block suspicious TNEF attachments, particularly those with unusual attribute structures or oversized data fields. Network-based security controls including intrusion detection systems and firewalls can be configured to monitor for patterns indicative of TNEF exploitation attempts. Additionally, application-level sandboxing and memory protection mechanisms should be considered to limit the potential impact of successful exploitation attempts. The vulnerability demonstrates the importance of proper input validation and bounds checking in security-critical code components, aligning with ATT&CK technique T1059.007 for command and scripting interpreter and T1203 for Exploitation for Client Execution, as attackers can leverage such flaws to execute malicious code through legitimate application interfaces. Regular security assessments and vulnerability scanning should be implemented to identify and remediate similar issues in other third-party libraries and components that may be vulnerable to similar out-of-bounds write conditions.