CVE-2006-4392 in Mac OS X
Summary
by MITRE
The Mach kernel, as used in operating systems including (1) Mac OS X 10.4 through 10.4.7 and (2) OpenStep before 4.2, allows local users to gain privileges via a parent process that forces an exception in a setuid child and uses Mach exception ports to modify the child's thread context and task address space in a way that causes the child to call a parent-controlled function.
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Analysis
by VulDB Data Team • 04/23/2026
The vulnerability described in CVE-2006-4392 represents a critical privilege escalation flaw within the Mach kernel implementation found in various operating systems including Mac OS X versions 10.4 through 10.4.7 and OpenStep before version 4.2. This issue stems from improper handling of Mach exception ports during the execution of setuid processes, creating a dangerous race condition that allows local attackers to manipulate the execution flow of privileged programs. The vulnerability specifically exploits the interaction between parent and child processes where the parent process can manipulate exception handling mechanisms to redirect execution control of the setuid child process.
The technical flaw manifests when a parent process creates a setuid child process and then establishes Mach exception ports to intercept and modify the child's execution context. During the normal execution flow, when the setuid child encounters an exception, the parent process can modify the thread context and task address space of the child through these exception ports. This manipulation allows the parent to effectively control where the child process will execute next, potentially redirecting it to call functions controlled by the attacker. The vulnerability is particularly dangerous because it leverages the legitimate exception handling mechanisms of the Mach kernel while exploiting the trust relationship between parent and child processes, making it difficult to detect through standard security monitoring.
The operational impact of this vulnerability is severe as it enables local users to escalate their privileges from regular user level to root level without requiring any special authentication or external exploitation vectors. An attacker can exploit this weakness by creating a malicious parent process that sets up the appropriate exception port handlers and then spawns a setuid child process such as those used for system administration or privilege-requiring operations. The successful exploitation results in complete system compromise where the attacker gains full administrative control over the affected system. This vulnerability directly relates to CWE-284 which describes improper access control, and specifically addresses weaknesses in privilege management and process control mechanisms.
The exploitation of this vulnerability aligns with several techniques described in the MITRE ATT&CK framework, particularly those related to privilege escalation and process injection. Attackers can leverage this flaw as part of a broader attack chain to establish persistent access and escalate their privileges within the system. The vulnerability also demonstrates characteristics of process manipulation techniques where attackers can modify the execution context of other processes to achieve unauthorized code execution. Organizations should note that this vulnerability was particularly concerning for systems running older versions of Mac OS X and OpenStep, as these versions did not implement the necessary protections against such exception port manipulation attacks. The flaw essentially bypasses traditional security boundaries by exploiting the kernel's legitimate exception handling capabilities to subvert privilege mechanisms.
Mitigation strategies for this vulnerability include applying the appropriate security patches and updates provided by Apple for Mac OS X versions 10.4.8 and later, as well as for OpenStep 4.2 and subsequent releases. System administrators should ensure that all affected systems are updated to versions that properly restrict the manipulation of exception ports by parent processes when dealing with setuid children. Additional protective measures include implementing process monitoring to detect unusual exception port configurations and restricting the ability of non-privileged processes to manipulate exception handling mechanisms. The vulnerability underscores the importance of proper kernel security design and the need for careful handling of privilege boundaries, particularly in systems that rely on complex inter-process communication mechanisms like Mach's exception ports. Organizations should also consider implementing additional security controls such as mandatory access controls and process integrity checking to prevent exploitation of similar privilege escalation vulnerabilities in their environments.