CVE-2026-85340 in Office
Summary
by MITRE • 10/14/2026
Use after free in Microsoft Office Click-To-Run 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 error within the Microsoft Office Click-to-Run service, which serves as the underlying infrastructure for deploying and managing Microsoft Office applications on Windows systems. This specific flaw arises from improper memory management practices where the application continues to access a block of memory after it has been freed or deallocated by the system. In the context of software engineering, this is classified under CWE-416, Use After Free, which represents one of the most dangerous classes of memory corruption vulnerabilities because it can lead to arbitrary code execution with significant consequences for system integrity and confidentiality.
The operational impact of this vulnerability is particularly severe due to its potential for local privilege escalation. An attacker who has already gained authorized access to a vulnerable system, such as through valid user credentials or by exploiting a preceding lower-privilege vulnerability, can leverage this memory corruption flaw to execute arbitrary code within the context of higher privileged processes. Since Microsoft Office Click-to-Run often runs with elevated privileges to facilitate seamless updates and installations across enterprise environments, successfully exploiting this use-after-free condition allows an attacker to bypass standard security boundaries and gain administrative control over the affected machine. This effectively transforms a low-level foothold into full system compromise, enabling the installation of malware, creation of new privileged accounts, or exfiltration of sensitive data stored on the local endpoint.
From a tactical perspective, this vulnerability aligns with MITRE ATT&CK techniques related to privilege escalation and process injection. Attackers typically utilize memory corruption vulnerabilities like use-after-free to manipulate control flow within running processes, often by overwriting function pointers or virtual table entries in heap structures that are still referenced but no longer validly allocated. The exploitation chain usually involves crafting a specific sequence of operations that triggers the premature deallocation while maintaining references to that memory region, thereby allowing the attacker to inject malicious payloads into the freed memory space which is subsequently reallocated for legitimate purposes controlled by the attacker.
Mitigation strategies primarily rely on applying vendor-supplied security patches and updates provided through Windows Update or Microsoft's dedicated update channels for Office products. Organizations should ensure that all endpoints running Microsoft Office Click-to-Run are configured to automatically receive critical security updates, thereby closing the memory management gap exploited by this vulnerability. Additionally, implementing strict application control policies such as AppLocker or Windows Defender Application Control can restrict the execution of untrusted scripts and binaries, limiting the ability of an attacker to execute arbitrary code even if they successfully exploit the underlying memory corruption flaw. Regular auditing of system privileges and monitoring for anomalous process behavior using endpoint detection and response solutions further enhances defense-in-depth against such privilege escalation attempts.