CVE-2016-6241 in OpenBSD
Summary
by MITRE
Integer overflow in the amap_alloc1 function in OpenBSD 5.8 and 5.9 allows local users to execute arbitrary code with kernel privileges via a large size value.
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Analysis
by VulDB Data Team • 12/05/2024
The vulnerability identified as CVE-2016-6241 represents a critical integer overflow flaw within the OpenBSD operating system kernel, specifically affecting versions 5.8 and 5.9. This vulnerability resides in the amap_alloc1 function which is part of the memory management subsystem responsible for allocating memory mappings. The flaw arises from inadequate input validation when processing large size values, creating a condition where an integer overflow can occur during memory allocation operations. The vulnerability is classified under CWE-190 as an integer overflow or wraparound, which directly enables privilege escalation from user-level to kernel-level execution privileges.
The technical implementation of this vulnerability involves the amap_alloc1 function failing to properly validate the size parameter passed to it during memory allocation requests. When a local user provides an excessively large size value, the integer arithmetic within the function can overflow, causing the allocated memory region to be improperly sized or positioned. This overflow condition can result in memory corruption that allows an attacker to manipulate kernel data structures or overwrite critical memory regions. The vulnerability specifically affects the kernel's memory mapping subsystem and can be exploited through kernel memory allocation interfaces that are accessible to local users.
From an operational perspective, this vulnerability presents a severe security risk as it enables local privilege escalation attacks that can result in complete system compromise. An attacker with local user access can leverage this vulnerability to gain kernel-level privileges, potentially leading to full system control, data exfiltration, or persistent backdoor installation. The attack vector is particularly concerning because it requires only local user access, making it accessible through various legitimate user contexts. The impact extends beyond immediate privilege escalation to include potential denial of service conditions, data integrity compromise, and the ability to bypass kernel security mechanisms such as memory protection and access controls.
Mitigation strategies for CVE-2016-6241 should prioritize immediate system updates to patched versions of OpenBSD 5.10 and later releases where the integer overflow has been corrected. System administrators should implement strict access controls and monitor for unusual memory allocation patterns that might indicate exploitation attempts. The vulnerability aligns with ATT&CK technique T1068 which describes local privilege escalation through kernel exploits, and T1059 which covers command and scripting interpreter usage. Additional protective measures include kernel hardening configurations, disabling unnecessary kernel modules, and implementing memory protection mechanisms such as stack canaries and address space layout randomization. Organizations should also conduct thorough security audits of their kernel memory management interfaces and ensure that all systems are running patched versions to prevent exploitation. The vulnerability demonstrates the importance of proper integer overflow checking in kernel code and highlights the critical need for comprehensive input validation in system-level programming.