CVE-2016-6240 in OpenBSD
Summary
by MITRE
Integer truncation error in the amap_alloc 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-2016-6240 represents a critical integer truncation flaw within the amap_alloc function of OpenBSD versions 5.8 and 5.9. This issue falls under the category of software security flaws that can lead to privilege escalation and arbitrary code execution. The vulnerability stems from improper handling of integer values during memory allocation operations, creating a pathway for malicious local users to gain kernel-level privileges. The flaw specifically manifests when processing large size values that exceed the range of the target integer type, resulting in unexpected behavior during memory management operations.
The technical implementation of this vulnerability involves the amap_alloc function which manages memory allocation for anonymous memory mappings. When a user provides a large size parameter, the integer truncation occurs during the conversion process, causing the system to interpret a large value as a much smaller one. This truncation creates a scenario where the kernel allocates insufficient memory space while the application attempts to use the full original size, leading to memory corruption and potential code execution. The flaw is classified as a CWE-190 - Integer Overflow or Wraparound, which represents a fundamental weakness in data handling that can result in unpredictable behavior and security exploits.
The operational impact of CVE-2016-6240 is severe as it enables local privilege escalation from user-level to kernel-level privileges. Attackers can leverage this vulnerability to execute arbitrary code with the highest system privileges, potentially leading to complete system compromise. The exploitation requires local access to the system but does not necessitate network connectivity or authentication, making it particularly dangerous in multi-user environments where users might have legitimate access to system resources. This vulnerability directly maps to ATT&CK technique T1068 - Exploitation for Privilege Escalation, where adversaries use software vulnerabilities to gain elevated privileges. The attack vector is classified as local privilege escalation through kernel exploitation, which can result in persistent system compromise and data exfiltration capabilities.
Mitigation strategies for CVE-2016-6240 primarily involve upgrading to OpenBSD versions that contain the patched implementation of the amap_alloc function. System administrators should immediately apply the official security patches released by OpenBSD to address this vulnerability. Additionally, implementing proper input validation and integer overflow checks in memory management functions can prevent similar issues in custom applications. The vulnerability highlights the importance of rigorous code review processes and formal verification of critical system components. Organizations should also consider implementing runtime protections such as stack canaries and address space layout randomization to complicate exploitation attempts. Regular security assessments and vulnerability scanning should be conducted to identify similar integer truncation issues in other system components and third-party applications. The fix typically involves ensuring proper bounds checking and type validation before integer conversions occur, preventing the truncation that leads to memory allocation errors and subsequent privilege escalation opportunities.