CVE-2018-17182 in Android
Summary
by MITRE
An issue was discovered in the Linux kernel through 4.18.8. The vmacache_flush_all function in mm/vmacache.c mishandles sequence number overflows. An attacker can trigger a use-after-free (and possibly gain privileges) via certain thread creation, map, unmap, invalidation, and dereference operations.
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Analysis
by VulDB Data Team • 12/07/2024
The vulnerability identified as CVE-2018-17182 represents a critical flaw in the Linux kernel version 4.18.8 and earlier, specifically within the virtual memory address management subsystem. This issue resides in the vmacache_flush_all function located in the mm/vmacache.c file, which serves as a crucial component for maintaining virtual memory address cache entries. The vulnerability stems from improper handling of sequence number overflows that occur during the management of virtual memory mappings, creating a window of opportunity for sophisticated exploitation techniques.
The technical flaw manifests when the kernel's virtual memory address cache fails to properly manage sequence numbers that track the validity of cached virtual memory entries. Sequence numbers are essential for ensuring that cached mappings remain consistent with actual memory mappings, but when these numbers overflow due to extended system operation or specific workload patterns, the cache management logic becomes corrupted. This overflow condition leads to a situation where the kernel may incorrectly determine that stale cached entries are still valid, resulting in improper memory management decisions. The vulnerability becomes exploitable when concurrent thread creation, memory mapping operations, unmapping activities, and invalidation procedures occur in specific sequences that trigger the corrupted cache state.
The operational impact of this vulnerability extends beyond simple memory corruption, as it creates a use-after-free condition that can potentially be leveraged for privilege escalation. When the sequence number overflow occurs, the kernel may attempt to access memory locations that have already been freed or reallocated, creating opportunities for attackers to manipulate the system's memory layout. This manipulation can enable attackers to execute arbitrary code with elevated privileges, potentially allowing full system compromise. The vulnerability is particularly dangerous because it can be triggered through legitimate kernel operations, making it difficult to detect and prevent through standard security monitoring mechanisms.
The exploitation of this vulnerability requires careful orchestration of memory management operations to force the sequence number overflow condition, typically involving multiple threads performing mapping and unmapping operations in specific patterns. This aligns with attack patterns documented in the attack tree methodology where attackers must establish a precise sequence of operations to create the conditions necessary for exploitation. The vulnerability has been classified under CWE-476 as a NULL Pointer Dereference, though the actual exploitation involves more complex memory management issues that can lead to privilege escalation. System administrators and security professionals should prioritize patching systems running Linux kernel versions up to 4.18.8, as the vulnerability represents a significant risk to system integrity and security posture. The fix implemented in newer kernel versions properly handles sequence number overflow conditions and ensures that virtual memory cache entries are correctly validated even during extended system operation periods.