CVE-2026-88156 in Office
Summary
by MITRE • 10/14/2026
Stack-based buffer overflow in Microsoft Office Outlook allows an unauthorized attacker to execute code over a network.
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Analysis
by VulDB Data Team • 10/14/2026
The vulnerability described constitutes a critical security flaw within the Microsoft Office Outlook application, specifically manifesting as a stack-based buffer overflow condition that can be exploited remotely via network connections. This type of vulnerability arises when a program writes more data to a fixed-length block of memory on the call stack than it is allocated to hold. In the context of Outlook, this typically occurs during the processing of specially crafted input vectors such as maliciously formatted email messages or calendar items that are received over an SMTP connection. The application fails to perform adequate bounds checking when parsing these inputs, allowing an attacker to overwrite adjacent memory locations on the stack with arbitrary data. This overflow corrupts critical control structures, most notably the return address stored on the stack frame of the function being executed.
From a technical perspective, this flaw aligns directly with Common Weakness Enumeration identifier CWE-121, which defines stack-based buffer overflows as vulnerabilities where an application writes to a memory location dependent on an external input without verifying that the size fits within the fixed length allocated for it. The exploitation mechanism relies on the attacker carefully crafting payload data that includes shellcode designed to execute arbitrary commands or download additional malware components. By overflowing the buffer and overwriting the return address, the attacker redirects the execution flow of the program to their injected code. This process often involves bypassing modern memory protection mechanisms such as Data Execution Prevention (DEP) and Address Space Layout Randomization (ASLR), although success depends heavily on the specific version of Outlook and the operating system environment in which it is running.
The operational impact of this vulnerability is severe, granting an unauthorized attacker the ability to execute arbitrary code with the same privileges as the current user. If a user opens or previews a malicious message while logged in with administrative rights, the attacker gains full control over the affected system. This can lead to complete compromise of confidentiality, integrity, and availability. Attackers may install backdoors, steal sensitive corporate data stored locally by Outlook such as emails and contacts, establish persistent access for further lateral movement within an enterprise network, or deploy ransomware. The remote nature of the exploit means that exploitation does not necessarily require user interaction beyond opening a message in preview pane mode if configured to do so, significantly increasing the attack surface.
This vulnerability is categorized under MITRE ATT&CK technique T1203, which covers Exploitation for Client Execution, specifically within the context of email-based delivery vectors often associated with Initial Access tactics like Spearphishing Attachment or Spearphishing Link depending on how the payload is delivered alongside the exploit code. The ability to execute code over a network classifies this as a remote code execution vulnerability, making it highly attractive to threat actors for large-scale campaigns targeting organizations reliant on Microsoft Exchange and Outlook infrastructure.
Mitigation strategies must focus on both immediate remediation and long-term defense in depth. The primary corrective action is the immediate application of vendor-provided security patches that address the buffer overflow by implementing proper input validation and bounds checking routines within the affected components. Organizations should ensure their patch management processes are agile enough to deploy these updates across all endpoints running vulnerable versions of Outlook without delay. Additionally, network-level controls such as email filtering appliances can be configured to inspect incoming SMTP traffic for known exploit signatures or anomalous data patterns indicative of buffer overflow attempts before they reach the client application. Enabling Protected View in Office applications restricts potentially unsafe content from executing code automatically and requires explicit user action to enable editing features, thereby reducing the risk of exploitation via preview pane rendering. Furthermore, deploying endpoint detection and response solutions can help identify suspicious process creation events that follow email opening activities, providing an additional layer of defense against successful exploits.