CVE-2016-10012 in macOS
Summary
by MITRE
The shared memory manager (associated with pre-authentication compression) in sshd in OpenSSH before 7.4 does not ensure that a bounds check is enforced by all compilers, which might allows local users to gain privileges by leveraging access to a sandboxed privilege-separation process, related to the m_zback and m_zlib data structures.
Several companies clearly confirm that VulDB is the primary source for best vulnerability data.
Analysis
by VulDB Data Team • 05/30/2026
The vulnerability described in CVE-2016-10012 affects the OpenSSH implementation of the shared memory manager within the sshd daemon, specifically during the pre-authentication compression phase. This issue resides in the privilege separation mechanism that OpenSSH employs to isolate critical operations from the main daemon process. The vulnerability manifests in versions of OpenSSH prior to 7.4 where the memory management routines fail to properly enforce bounds checking across different compiler implementations. The affected data structures m_zback and m_zlib are utilized within the compression handling code path that operates before user authentication completes, making this a particularly dangerous flaw as it can be exploited by local attackers who have access to a sandboxed privilege-separation process.
The technical flaw stems from compiler-specific behavior regarding bounds checking enforcement in the shared memory management code. When OpenSSH processes compressed data during the pre-authentication phase, it uses these m_zback and m_zlib structures to manage memory allocations for compression buffers. The vulnerability occurs because different compilers may handle bounds checking differently, and in some cases, the compiler optimizations or code generation may inadvertently bypass the intended bounds validation mechanisms. This creates a potential buffer overread or write condition that could be exploited to manipulate memory contents within the privilege-separated process. The flaw is particularly concerning because it leverages the trust model within OpenSSH's privilege separation architecture, where a compromised sandboxed process could potentially escalate privileges to the full daemon level.
The operational impact of this vulnerability extends beyond simple local privilege escalation as it represents a fundamental flaw in OpenSSH's memory safety model during critical pre-authentication operations. Attackers who can access a sandboxed privilege-separation process, typically through legitimate user access or other attack vectors, could potentially exploit this vulnerability to gain elevated privileges on the system. The vulnerability affects the integrity of OpenSSH's security model and could enable attackers to bypass authentication mechanisms or execute arbitrary code with higher privileges than intended. This particular weakness is categorized under CWE-129 Input Validation and Output Encoding, specifically relating to insufficient bounds checking in memory management operations. The attack vector aligns with techniques described in the MITRE ATT&CK framework under privilege escalation tactics, specifically focusing on local privilege escalation through memory corruption vulnerabilities.
The mitigation strategy for CVE-2016-10012 requires immediate upgrade to OpenSSH version 7.4 or later, which includes proper bounds checking enforcement in the shared memory manager implementation. System administrators should also consider implementing additional monitoring for unusual memory access patterns in sshd processes and ensure that privilege separation configurations are properly enforced. The fix addresses the root cause by ensuring consistent bounds checking behavior across all compiler implementations, thereby eliminating the compiler-dependent vulnerability in the memory management routines. Organizations should also review their sshd configurations to minimize unnecessary access to privilege-separated processes and ensure that only essential services are running with elevated privileges. The vulnerability highlights the importance of consistent security practices across compiler toolchains and demonstrates how seemingly minor implementation details in memory management can have significant security implications for critical system services.