CVE-2016-1738 in Mac OS X
Summary
by MITRE
dyld in Apple OS X before 10.11.4 allows attackers to bypass a code-signing protection mechanism via a modified app.
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Analysis
by VulDB Data Team • 07/11/2022
The vulnerability identified as CVE-2016-1738 resides within the dynamic link editor dyld component of Apple's operating system, specifically affecting versions prior to macOS 10.11.4. This flaw represents a significant bypass of the code-signing protection mechanisms that are fundamental to macOS security architecture. The dyld component is responsible for loading dynamic shared libraries and managing the dynamic linking process in macOS applications, making it a critical element in the system's security model. When an application is properly code-signed, the system verifies the digital signature to ensure the software originates from a trusted source and has not been tampered with since signing. The vulnerability allows malicious actors to circumvent this verification process through careful manipulation of application files.
The technical nature of this vulnerability stems from improper validation of code-signing certificates during the dynamic linking process. Attackers can exploit this weakness by creating modified applications that appear legitimate to the system's code-signing verification mechanisms. The flaw specifically affects how dyld processes and validates signature information when loading shared libraries, allowing attackers to inject malicious code or modify existing functionality without triggering the system's security warnings. This represents a direct violation of the principle of least privilege and undermines the integrity protection mechanisms that are essential for preventing unauthorized code execution. The vulnerability operates at a low level within the operating system, making it particularly dangerous as it can be exploited without requiring elevated privileges or specific user interactions beyond launching the modified application.
The operational impact of CVE-2016-1738 extends beyond simple code execution, as it enables sophisticated attack vectors that can lead to complete system compromise. Attackers can leverage this vulnerability to bypass security controls that are supposed to prevent malicious software from running on the system, effectively allowing them to install backdoors, steal sensitive data, or perform other malicious activities without detection. The vulnerability is particularly concerning because it affects the core system components that are essential for proper operating system function, meaning that any application could potentially be used as a vector for exploitation. This flaw aligns with the attack pattern described in the ATT&CK framework under the technique of "Exploitation for Privilege Escalation" and falls under the broader category of code injection vulnerabilities that can be classified as CWE-431.
Organizations and individuals affected by this vulnerability should immediately update to macOS 10.11.4 or later versions where Apple has implemented proper code-signing validation mechanisms. The fix addresses the root cause by strengthening the verification process within dyld to ensure that all dynamically loaded libraries maintain valid code-signing certificates. System administrators should also implement additional monitoring measures to detect suspicious application behavior, particularly around code-signing validation failures or unexpected library loading patterns. Security professionals should consider this vulnerability as part of their comprehensive threat modeling exercises, particularly when evaluating the risk of supply chain attacks or insider threats that might exploit such fundamental system flaws. The vulnerability demonstrates the critical importance of maintaining up-to-date operating systems and the potential consequences of delayed patch management in enterprise security environments.