CVE-2026-88109 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 updates for various 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 typical software execution flows, when an object is no longer needed, its allocated memory should be released back to the operating system for reuse. However, if pointers referencing this now-invalidated memory location are not nullified or properly managed, subsequent operations may attempt to read from or write to that freed region. This creates a window of opportunity where the state of the program becomes unpredictable and potentially exploitable by malicious actors who can influence the allocation patterns in that specific memory space.
From an operational perspective, this vulnerability is particularly dangerous because it resides within a component that often runs with elevated privileges as part of the system's update mechanism or administrative management tools. When an authorized attacker gains access to the local environment where Microsoft Office Click-to-Run operates, they can craft a malicious payload designed to trigger the use-after-free condition. By carefully controlling the data written into the freed memory region before it is reallocated for another purpose, the attacker can manipulate critical control flow structures such as function pointers or virtual table entries. This manipulation allows the execution of arbitrary code within the security context of the vulnerable process. Since these processes frequently operate with higher privilege levels than standard user accounts, successfully exploiting this flaw enables local privilege escalation, granting the attacker administrative rights over the compromised system without requiring additional authentication vectors.
This type of vulnerability is classified under CWE-416, which denotes Use After Free errors in software development. The exploitation technique aligns closely with ATT&CK tactic T1055, specifically sub-techniques related to process injection or memory manipulation for privilege escalation. Attackers typically leverage this flaw during the post-exploitation phase after gaining initial foothold access through other means such as phishing or network vulnerabilities. The impact extends beyond simple code execution; it compromises the integrity and confidentiality of the entire system by allowing unauthorized administrative actions, installation of persistent backdoors, lateral movement to other systems on the network, and exfiltration of sensitive data stored locally or accessible via elevated credentials.
Mitigation strategies for this vulnerability primarily involve applying the latest security patches released by Microsoft through Windows Update or manual download from the official support portal. Organizations should ensure that their patch management policies are rigorous and timely, particularly for components involved in software deployment and system administration. Additionally, implementing strict application control policies using tools like AppLocker or Windows Defender Application Control can restrict the execution of untrusted binaries even if an attacker manages to exploit this vulnerability. Network segmentation and least privilege principles further reduce risk by limiting the potential blast radius should a local account be compromised. Regular auditing of installed software versions and monitoring for anomalous process behavior associated with Office Click-to-Run services can also aid in early detection of exploitation attempts.