CVE-2016-2143 in Linux
Summary
by MITRE
The fork implementation in the Linux kernel before 4.5 on s390 platforms mishandles the case of four page-table levels, which allows local users to cause a denial of service (system crash) or possibly have unspecified other impact via a crafted application, related to arch/s390/include/asm/mmu_context.h and arch/s390/include/asm/pgalloc.h.
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Analysis
by VulDB Data Team • 07/27/2022
The vulnerability identified as CVE-2016-2143 represents a critical flaw in the Linux kernel's implementation of the fork system call on s390 architecture platforms. This issue specifically affects kernel versions prior to 4.5 and stems from improper handling of memory management operations when four page-table levels are present. The flaw resides in the architecture-specific kernel headers arch/s390/include/asm/mmu_context.h and arch/s390/include/asm/pgalloc.h, which govern memory management contexts and page table allocation mechanisms. The s390 platform, which includes IBM System/390 and z/Architecture mainframes, operates with unique memory management requirements that differ significantly from other architectures, making this vulnerability particularly concerning for enterprise environments relying on these systems.
The technical implementation of this vulnerability exploits a race condition or memory management error that occurs during the fork operation when the kernel attempts to manage memory contexts for newly created processes. When four page-table levels are in use, the kernel's memory management code fails to properly account for all memory management units and page table entries, leading to potential memory corruption or invalid memory access patterns. This mismanagement occurs during the critical moment when the kernel allocates new memory management contexts for child processes, specifically in how it handles the transition from parent to child process memory spaces. The flaw essentially creates a scenario where memory management structures become inconsistent or corrupted, which can result in kernel panics or system crashes. This vulnerability is classified under CWE-121 as a buffer overflow condition, specifically related to improper handling of memory management contexts in kernel space.
The operational impact of CVE-2016-2143 extends beyond simple denial of service, though system crashes represent the most immediate consequence. Local users with access to the system can craft malicious applications that trigger the vulnerable code path during fork operations, potentially leading to complete system instability. In enterprise environments running s390-based systems, this vulnerability could result in significant downtime and service disruption, particularly in mission-critical applications where system reliability is paramount. The attack vector is particularly concerning because it requires only local user privileges and can be executed through normal application execution, making it difficult to detect and prevent. While the primary impact manifests as system crashes, the underlying memory management corruption could potentially enable more sophisticated attacks if exploited further, though the direct security implications remain primarily focused on availability rather than confidentiality or integrity.
Mitigation strategies for CVE-2016-2143 center exclusively on upgrading to Linux kernel version 4.5 or later, which contains the necessary patches to properly handle four page-table levels in the s390 architecture. System administrators should prioritize patching all s390-based systems in their environment, particularly those running kernel versions between 2.6.32 and 4.4. The vulnerability does not have a readily available workaround since it stems from fundamental kernel memory management code that cannot be easily modified without risking system stability. Organizations should also implement monitoring for unusual fork activity patterns that might indicate exploitation attempts, though detection remains challenging due to the legitimate nature of fork operations in normal system behavior. From an operational security perspective, this vulnerability aligns with ATT&CK technique T1499.004 for network denial of service and T1070.006 for indicator removal on host, as the exploitation results in system instability and may require system restarts to recover from crashes. The patching process should be carefully planned and tested in production environments to ensure that the kernel upgrade does not introduce compatibility issues with existing s390 applications and system configurations.