CVE-2026-83917 in Windows
Summary
by MITRE • 10/14/2026
Use after free in Windows ALPC allows an authorized attacker to elevate privileges locally.
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Analysis
by VulDB Data Team • 10/14/2026
The vulnerability described involves a use-after-free condition within the Local Procedure Call (ALPC) mechanism of Microsoft Windows, which can be exploited by an authenticated local user to achieve arbitrary code execution and subsequently escalate privileges to that of the SYSTEM account. ALPC is a core inter-process communication subsystem in Windows responsible for facilitating secure data exchange between processes running at different integrity levels, such as those within the client-server runtime server (csrss.exe) or other critical system components. The flaw arises when memory allocated for an ALPC message structure is freed while references to that same memory block remain active and accessible by another thread or process context. This race condition allows an attacker to manipulate the contents of the now-dangling pointer, effectively controlling what data is processed after the original allocation has been reclaimed by the system's memory manager.
From a technical perspective, this defect falls under CWE-416, Use After Free, which describes situations where software continues to use pointers that point to freed memory. In the context of ALPC, an attacker can craft specific RPC calls or message structures designed to trigger the premature deallocation of internal buffers while maintaining control over subsequent operations on those buffers. By carefully timing the allocation and freeing of these objects, often through rapid successive requests, the attacker can cause the system to reallocate that memory with controlled data provided by the malicious process. When the vulnerable code path subsequently accesses this pointer under the assumption it still holds valid ALPC metadata or command structures, it inadvertently executes instructions derived from the attacker's input rather than legitimate system operations.
The operational impact of exploiting this vulnerability is severe, as it enables local privilege escalation without requiring physical access to the machine or external network connectivity beyond what an authenticated user already possesses. Once arbitrary code execution is achieved within a privileged context such as SYSTEM, the attacker gains complete control over the operating system. This includes the ability to install programs, view, change, or delete any data on the affected system, and create new accounts with full administrative rights. Such compromise effectively nullifies all security boundaries enforced by Windows integrity levels, allowing persistent access and lateral movement within a network environment if this machine serves as a pivot point for further attacks against other systems.
This vulnerability aligns with MITRE ATT&CK technique T1068 Exploitation for Privilege Escalation, specifically under the sub-technique of exploiting software vulnerabilities to gain higher-level access. Defense strategies must prioritize immediate patching through official Microsoft security updates that address this specific ALPC handling defect. Organizations should ensure their Windows endpoints are configured with automatic update policies enabled and regularly scanned for missing patches. Additionally, implementing strict application whitelisting can mitigate the risk by preventing unauthorized executables from running even if an attacker gains initial access via other means. Monitoring for unusual process creation events originating from system processes or unexpected RPC activity may also help detect exploitation attempts in real-time before full compromise occurs.