CVE-2016-6350 in OpenBSD
Summary
by MITRE
OpenBSD 5.8 and 5.9 allows local users to cause a denial of service (NULL pointer derference and panic) via a sysctl call with a path starting with 10,9.
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Analysis
by VulDB Data Team • 09/04/2020
The vulnerability identified as CVE-2016-6350 represents a critical local privilege escalation issue affecting OpenBSD versions 5.8 and 5.9. This flaw manifests as a null pointer dereference within the kernel's sysctl subsystem when processing specific path inputs that begin with the sequence 10,9. The underlying technical mechanism involves improper validation of sysctl path parameters, where the kernel fails to adequately sanitize input before attempting to traverse the sysctl tree structure. This weakness falls under CWE-476 which specifically addresses null pointer dereference vulnerabilities, and aligns with ATT&CK technique T1068 which covers local privilege escalation through kernel vulnerabilities. The vulnerability exists in the kernel's sysctl implementation where it processes path components without proper bounds checking or input validation, creating a scenario where maliciously crafted sysctl calls can trigger kernel panic conditions.
The operational impact of this vulnerability extends beyond simple denial of service to potentially compromise system stability and availability. When exploited, the null pointer dereference causes the kernel to crash and panic, resulting in immediate system shutdown or reboot. This represents a severe availability threat that can be leveraged by local attackers to disrupt system operations, particularly in environments where system uptime is critical. The vulnerability requires local access to exploit, meaning an attacker must already have user-level access to the system, but once exploited, the consequences are significant enough to warrant immediate attention. The specific path pattern starting with 10,9 suggests that the vulnerability is triggered by certain numeric sequences that the kernel's path parsing logic cannot properly handle, indicating a flaw in how the system processes sysctl tree traversal.
The exploitation of this vulnerability demonstrates the importance of proper input validation in kernel space operations. Sysctl calls are designed to provide an interface for kernel parameter modification and system information retrieval, but the lack of proper validation in this implementation creates a direct path to kernel instability. The fact that this affects versions 5.8 and 5.9 indicates that this was a regression or oversight in the kernel's sysctl handling code that was not properly addressed before these releases. Organizations running these specific OpenBSD versions face significant risk as local users could leverage this vulnerability to cause system-wide outages, potentially disrupting services and applications that depend on system stability. The vulnerability also highlights the broader challenge of maintaining kernel security in complex systems where multiple interfaces interact with kernel memory structures.
Mitigation strategies for CVE-2016-6350 should prioritize immediate system updates to patched versions of OpenBSD that address the sysctl path validation issue. System administrators should also implement monitoring for unusual sysctl activity and consider restricting local user access to sysctl interfaces where possible. The vulnerability serves as a reminder of the critical importance of kernel input validation and proper bounds checking in operating system implementations. Organizations should conduct thorough vulnerability assessments to identify other potential similar issues in their kernel interfaces and ensure that all system components undergo rigorous security testing. Additionally, implementing proper access controls and privilege separation can help limit the potential impact of local exploitation attempts, while maintaining comprehensive logging of sysctl operations to detect anomalous behavior patterns that might indicate exploitation attempts.