CVE-2019-12817 in Linux
Summary
by MITRE
arch/powerpc/mm/mmu_context_book3s64.c in the Linux kernel before 5.1.15 for powerpc has a bug where unrelated processes may be able to read/write to one another's virtual memory under certain conditions via an mmap above 512 TB. Only a subset of powerpc systems are affected.
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Analysis
by VulDB Data Team • 10/07/2023
The vulnerability identified as CVE-2019-12817 represents a critical memory management flaw within the Linux kernel's powerpc architecture implementation, specifically affecting systems utilizing the book3s64 memory management unit context handling. This issue resides in the arch/powerpc/mm/mmu_context_book3s64.c file and impacts kernel versions prior to 5.1.15, creating a serious security risk where process isolation mechanisms can be bypassed under specific conditions. The flaw manifests when memory mappings occur above the 512 terabyte address boundary, allowing for potential information disclosure and unauthorized data access between unrelated processes.
The technical nature of this vulnerability stems from improper handling of memory management unit contexts in the powerpc architecture's 64-bit implementation. When processes attempt to map memory regions above the 512 TB boundary, the kernel fails to properly invalidate or manage the memory context associations, leading to potential cross-process memory access. This represents a classic case of inadequate memory isolation where the kernel's memory management subsystem does not properly enforce the separation between different process virtual address spaces. The vulnerability is particularly concerning because it operates at the kernel level within the memory management subsystem, making it difficult to detect and exploit through conventional means while still providing substantial attack surface for privilege escalation.
The operational impact of this vulnerability extends beyond simple information disclosure, potentially enabling complete system compromise through memory read/write operations between processes. An attacker could leverage this flaw to access sensitive data belonging to other processes, including cryptographic keys, passwords, or confidential application data. The affected systems are limited to specific powerpc configurations, but within those environments, the vulnerability poses a significant risk to system integrity and confidentiality. According to CWE classification, this vulnerability maps to CWE-284: Improper Access Control, specifically manifesting as inadequate process isolation within kernel memory management. The ATT&CK framework would categorize this under T1068: Exploitation for Privilege Escalation, as the vulnerability could be exploited to gain unauthorized access to memory resources that should be isolated.
Mitigation strategies for CVE-2019-12817 require immediate kernel updates to version 5.1.15 or later, which contain the necessary patches to properly handle memory context management for mappings above the 512 TB boundary. System administrators should prioritize patching affected powerpc systems, particularly those running kernel versions between 4.19 and 5.1.14. Additional protective measures include monitoring for unusual memory mapping patterns above 512 TB boundaries and implementing process isolation controls where possible. Organizations should also consider implementing memory access controls and monitoring for unauthorized memory access patterns that could indicate exploitation attempts. The patch addresses the root cause by ensuring proper invalidation of memory management unit contexts when dealing with high-address mappings, thereby restoring proper process isolation mechanisms. Security teams should conduct thorough vulnerability assessments of powerpc systems to identify any remaining instances of affected kernel versions and ensure comprehensive system hardening measures are implemented to prevent exploitation of similar memory management vulnerabilities.