CVE-2026-85791 in Windows
Summary
by MITRE • 10/14/2026
Heap-based buffer overflow in Windows Encrypting File System (EFS) 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 heap-based buffer overflow within the Microsoft Windows Encrypting File System, commonly referred to as EFS. This component is responsible for providing file system-level encryption that protects data from unauthorized access by encrypting files on disk using symmetric keys and asymmetric public-key cryptography. The specific flaw resides in how EFS processes certain inputs or handles memory allocation during cryptographic operations or metadata management tasks. A heap-based buffer overflow occurs when a program writes more data to a block of memory allocated on the heap than it can hold, causing adjacent memory locations to be overwritten with unintended values. In this context, an attacker who has already gained authorized access to the system can exploit this improper boundary check and memory handling mechanism to corrupt critical process structures or control flow pointers stored in the heap space.
The operational impact of this vulnerability is severe because it facilitates local privilege escalation. Although the initial attack vector requires authentication, meaning the adversary must possess valid user credentials on the target machine, the ability to execute arbitrary code with elevated privileges effectively compromises the entire system integrity. By leveraging the buffer overflow, an attacker can manipulate execution flow to run malicious payloads in a higher security context, typically that of SYSTEM or Administrator. This allows for complete control over the operating system, enabling actions such as installing programs, viewing, changing, or deleting confidential data, and creating new accounts with full administrative rights. The presence of EFS adds complexity because the exploit must interact correctly with cryptographic libraries and file handling routines without triggering immediate detection by standard security monitors that might not expect memory corruption in this specific subsystem.
From a classification perspective, this vulnerability aligns closely with CWE-122, which denotes heap-based buffer overflow, indicating an issue where data is written beyond the allocated boundary of a dynamically allocated block of memory. Furthermore, the exploitation technique maps to MITRE ATT&CK techniques associated with privilege escalation and code execution via memory corruption. Specifically, it relates to methods that abuse system components or libraries to bypass security restrictions. The attack path typically involves crafting specific requests or file operations that trigger the vulnerable function within EFS, leading to the overflow condition. Once triggered, the attacker utilizes shellcode injected into the heap to gain control over instruction pointers, thereby achieving code execution in a privileged context.
Mitigation strategies for this vulnerability primarily involve applying vendor-supplied security patches and updates released by Microsoft to address the underlying coding errors in the EFS component. Organizations should ensure that all systems are updated with the latest cumulative updates to close known gaps in memory management routines. Additionally, implementing strict access control policies can limit the number of users who have local administrative privileges or high-level file system permissions, thereby reducing the attack surface for authenticated adversaries. Deploying endpoint detection and response solutions capable of monitoring for anomalous heap activity or unusual privilege escalation attempts can also provide an additional layer of defense against exploitation attempts that bypass traditional perimeter security measures.