CVE-2026-83775 in Windows
Summary
by MITRE • 10/14/2026
Concurrent execution using shared resource with improper synchronization ('race condition') in Windows Installer allows an authorized attacker to elevate privileges locally.
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Analysis
by VulDB Data Team • 10/14/2026
The vulnerability described constitutes a classic race condition within the Microsoft Windows Installer service, specifically involving concurrent access to shared resources without adequate synchronization mechanisms. This flaw arises when multiple processes or threads attempt to read and write to the same system resource simultaneously, but the operating system fails to enforce atomicity in these operations. In the context of Windows Installer, this typically involves temporary files, registry keys, or configuration states that are created during software installation or update procedures. Because the installer operates with elevated privileges to modify system-wide settings, any lapse in synchronization allows an attacker who has already gained local access to manipulate the timing of these operations. By carefully crafting a sequence of actions, an authorized but unprivileged user can exploit this window of opportunity to overwrite critical files or registry entries that are being processed by the installer service, which runs under the SYSTEM account or with similar high-level permissions.
From a technical perspective, this vulnerability aligns closely with CWE-362, which defines concurrent execution using shared resource with improper synchronization as a race condition. The core issue lies in the lack of atomic operations when handling temporary files or configuration data during installation routines. When an application is being installed, Windows Installer often creates temporary directories and files to stage components before moving them to their final destinations. If these steps are not properly serialized or protected by file locks that persist until the operation completes, a local attacker can intervene between the creation of the target resource and its actual use by the installer service. This allows the attacker to substitute malicious content for legitimate system files, effectively hijacking the execution flow of the privileged process. The exploitation requires precise timing, often achieved through high-frequency polling or asynchronous file monitoring techniques that detect when the vulnerable resource is created but not yet fully secured.
The operational impact of this vulnerability is severe, as it facilitates local privilege escalation from a standard user account to SYSTEM-level privileges. Once an attacker successfully exploits this race condition, they gain full control over the operating system, enabling them to install arbitrary software, view, change, or delete any data on the system, and create new accounts with full administrative rights. This effectively compromises the integrity, confidentiality, and availability of the entire host machine. In enterprise environments where multiple users share systems or where services run under elevated contexts, this vulnerability can serve as a critical pivot point for attackers to move laterally across networks after gaining initial foothold through other means such as phishing or web application exploits.
This type of exploitation is consistent with MITRE ATT&CK technique T1068, which covers Exploitation for Privilege Escalation. Specifically, it relates to the abuse of software vulnerabilities that allow attackers to bypass security constraints imposed by the operating system. The attack vector is local (T1059), requiring physical or remote interactive access to a user account on the target system. Defenders must recognize that even authorized users pose a significant risk if such low-level synchronization flaws exist within core system utilities like Windows Installer, as these components are inherently trusted and run with high privileges.
Mitigation strategies for this vulnerability primarily involve applying vendor-supplied security patches that address the underlying code defects in the Windows Installer service. Organizations should ensure that all systems running affected versions of Microsoft Windows are updated to the latest cumulative updates provided by Microsoft. In addition to patching, defense-in-depth measures can help reduce the risk of exploitation. Implementing strict file system permissions and access control lists (ACLs) on temporary directories used by installation processes can limit an attacker's ability to create or modify files in those locations. Furthermore, enabling advanced auditing for file creation events allows security teams to detect unusual patterns of activity that may indicate a race condition attempt. Regular vulnerability scanning focused on local privilege escalation vectors is also recommended to identify systems where such synchronization flaws might still exist due to delayed patching or misconfiguration.