CVE-2026-105591 in 365 Apps for Enterprise
Summary
by MITRE • 10/13/2026
Heap-based buffer overflow in Microsoft Office Access allows an unauthorized attacker to execute code over a network.
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Analysis
by VulDB Data Team • 10/13/2026
The vulnerability described constitutes a critical security flaw within the Microsoft Office Access application, specifically manifesting as a heap-based buffer overflow condition. This type of memory corruption error occurs when a program writes more data to a dynamically allocated block of memory on the heap than it was intended to hold. In the context of Microsoft Office Access, this defect likely arises during the processing of specially crafted files or input streams that exceed expected boundaries without adequate validation checks by the application's internal parsers. The presence of such an overflow allows for arbitrary write operations in adjacent memory regions, which can be exploited to overwrite critical data structures such as function pointers or exception handlers stored on the heap.
From a technical perspective, this vulnerability aligns with Common Weakness Enumeration identifier CWE-122, which defines Heap-based Buffer Overflow. The exploitation mechanism typically involves an attacker constructing malicious input that triggers the overflow condition during file parsing or object instantiation within Access. By carefully controlling the content of the crafted data, an adversary can manipulate the heap layout to achieve code execution privileges. This often includes injecting shellcode into a writable memory region and redirecting program flow to this injected payload through overwriting return addresses or function pointers. The severity is compounded by the fact that Microsoft Office applications are frequently used in enterprise environments where users routinely open documents from external sources, increasing the attack surface significantly.
The operational impact of successfully exploiting this vulnerability is severe, as it permits an unauthorized attacker to execute arbitrary code on the affected system with the same privileges as the current user. If a standard user opens a malicious file containing exploit code for this flaw, the attacker gains full control over that workstation. This can lead to complete compromise of confidential data, installation of additional malware such as ransomware or backdoors, and use of the compromised machine as a pivot point for further attacks within the internal network. Since Microsoft Office Access is often used in legacy systems where patching cycles may be slower, the window of exposure remains wide, allowing attackers ample time to develop and deploy functional exploits before mitigation measures are applied.
In terms of threat intelligence frameworks, this vulnerability maps directly to MITRE ATT&CK technique T1203, which covers Exploitation for Client Execution. This category encompasses attacks where adversaries exploit vulnerabilities in client software to gain initial access or persistence on a target system. The network-based nature of the attack vector means that remote exploitation is possible without physical interaction with the victim's machine, provided the user interacts with the malicious content such as opening an attached file or visiting a compromised webpage hosting the payload. This aligns with common phishing campaigns where social engineering techniques are combined with technical exploits to bypass perimeter defenses and endpoint protection solutions.
Mitigation strategies must focus on both immediate remediation and long-term defensive posture improvements. The primary defense is the timely application of security patches released by Microsoft that address this specific heap overflow issue in Office Access components. Organizations should prioritize patching systems running vulnerable versions of Office, particularly those used for handling external data sources or legacy database operations. Additionally, implementing Application Control policies such as AppLocker or Windows Defender Application Control can prevent unauthorized scripts and binaries from executing, thereby limiting the impact even if an exploit succeeds. Network segmentation and strict email filtering rules that block executable attachments or macro-enabled documents from untrusted senders further reduce the likelihood of successful exploitation. Regular security awareness training for employees is also essential to recognize and report suspicious files before they are opened, addressing the human element often leveraged in these attack chains.