CVE-2016-6245 in OpenBSD
Summary
by MITRE
OpenBSD 5.8 and 5.9 allows local users to cause a denial of service (kernel panic) via a large size in a getdents system call.
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Analysis
by VulDB Data Team • 08/18/2020
The vulnerability identified as CVE-2016-6245 represents a critical denial of service flaw affecting OpenBSD versions 5.8 and 5.9. This issue manifests through improper handling of system call parameters within the kernel, specifically when processing the getdents system call which is used to read directory entries. The vulnerability stems from insufficient validation of the buffer size parameter passed to this system call, creating a condition where malicious input can trigger kernel panic conditions. The flaw operates at the kernel level and requires local user access, making it particularly concerning for systems where untrusted users might have shell access or execute code within the operating environment. This vulnerability directly impacts system stability and availability, as successful exploitation results in immediate system crashes that require manual reboot to restore normal operations.
The technical implementation of this vulnerability resides in the kernel's directory entry reading mechanism where the getdents system call fails to properly validate the size parameter provided by userspace applications. When an attacker supplies an excessively large size value to the getdents system call, the kernel's internal buffer management routines become overwhelmed, leading to memory corruption and ultimately a kernel panic. This behavior aligns with CWE-129, which describes improper validation of length parameters, and specifically relates to improper input validation in kernel space operations. The vulnerability demonstrates how seemingly benign system calls can become vectors for system compromise when input validation is insufficient, particularly when dealing with user-supplied buffer sizes that should be strictly bounded.
The operational impact of CVE-2016-6245 extends beyond simple service disruption as it represents a fundamental stability issue within the OpenBSD kernel. Local attackers can reliably trigger kernel panics, effectively rendering systems unavailable to legitimate users until manual intervention occurs. This vulnerability is particularly dangerous in server environments where system uptime is critical, as it allows for persistent denial of service attacks that can be executed repeatedly without requiring elevated privileges. The attack surface is broad since any local user can potentially exploit this vulnerability, making it a significant concern for multi-user systems, development environments, or any scenario where users might have shell access. The vulnerability also has implications for system hardening efforts and compliance with security standards that require robust input validation and error handling.
Mitigation strategies for CVE-2016-6245 primarily involve upgrading to patched versions of OpenBSD where the kernel properly validates the size parameter in getdents system calls. System administrators should prioritize applying the official security patches released by OpenBSD to address this vulnerability. Additionally, implementing proper input validation at the application level can provide defense-in-depth measures, though this is secondary to the kernel-level fix. The vulnerability's classification under ATT&CK technique T1499.004 for network denial of service and T1068 for local privilege escalation highlights the need for comprehensive system hardening practices. Organizations should also consider implementing monitoring solutions that can detect kernel panic events and alert administrators to potential exploitation attempts, while maintaining regular security updates and patch management processes to prevent similar vulnerabilities from emerging in other system components.