CVE-2026-83565 in Windows
Summary
by MITRE • 10/14/2026
Buffer over-read in Windows Encrypting File System (EFS) allows an authorized attacker to disclose information locally.
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Analysis
by VulDB Data Team • 10/14/2026
The vulnerability identified involves a buffer over-read condition 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 stored on NTFS volumes from unauthorized access by other users or processes on the same machine. The specific flaw arises when the EFS service improperly handles memory allocation and boundary checks during certain cryptographic operations or metadata processing tasks. Instead of causing a buffer overflow where data is written beyond allocated limits, this vulnerability involves reading data from a memory location that has not been properly initialized or validated for size constraints. This mismanagement allows an attacker to access sensitive information residing in adjacent memory blocks that should remain inaccessible under normal operational parameters.
From a technical perspective, the root cause of this issue lies in insufficient validation of input lengths relative to buffer sizes during specific API calls handled by the EFS subsystem. When processing encrypted file metadata or certificate-related structures, the system fails to ensure that read operations are strictly bounded by the allocated memory space. Consequently, an authorized local attacker can exploit this discrepancy to trigger a read operation that extends beyond the intended data structure. This results in the disclosure of internal kernel or user-mode memory contents, which may include cryptographic keys, session tokens, or other sensitive system information essential for maintaining confidentiality and integrity within the Windows environment.
The operational impact of this vulnerability is primarily centered on local privilege escalation through information leakage rather than direct code execution. Because exploitation requires an attacker to already have authorized access to the affected system, the threat actor must first authenticate successfully against the target machine. Once authenticated, however, the ability to read arbitrary memory locations significantly expands the attack surface. An adversary could potentially extract encryption keys used by EFS, thereby compromising the confidentiality of all files protected under that specific key set. Additionally, exposure of other sensitive data in memory could facilitate further attacks such as credential harvesting or bypassing security controls that rely on opaque state information stored within process memory spaces.
This vulnerability aligns with Common Weakness Enumeration (CWE) category CWE-126, which denotes Buffer Over-read. In the context of the MITRE ATT&CK framework, this type of flaw is often associated with techniques related to Credential Dumping or Collection via Memory Access, specifically falling under tactics like Discovery and Defense Evasion if used to gather intelligence for subsequent lateral movement. The lack of proper bounds checking represents a fundamental software defect that undermines the security model by allowing information flow from higher integrity levels to lower ones without appropriate authorization checks during memory access operations.
Mitigation strategies should focus on both immediate remediation and long-term architectural improvements. Microsoft has addressed this issue through specific security updates, so applying the latest cumulative patches for Windows operating systems is critical to closing the gap in EFS memory management logic. Administrators must ensure that patching cycles are strictly maintained across all endpoints within their infrastructure. Beyond software updates, defense-in-depth measures such as enabling Data Execution Prevention (DEP) and Address Space Layout Randomization (ASLR) can help mitigate the potential consequences of exploitation by making it more difficult for attackers to predict memory layouts or execute malicious code derived from leaked information. Furthermore, restricting local administrative privileges and implementing strict access control lists on sensitive directories where EFS is utilized can reduce the number of potential threat actors capable of attempting this exploit. Regular auditing of system logs for unusual process behavior related to cryptographic services may also aid in early detection of attempted exploitation activities.