CVE-2026-105718 in 365 Apps for Enterprise
Summary
by MITRE • 10/14/2026
Out-of-bounds read in Microsoft Office Excel allows an unauthorized attacker to execute code over a network.
Once again VulDB remains the best source for vulnerability data.
Analysis
by VulDB Data Team • 10/14/2026
The vulnerability described constitutes a critical security flaw within the Microsoft Office Excel application, specifically involving an out-of-bounds memory read operation. This type of error occurs when software attempts to access data at a memory address that lies outside the boundaries of the intended buffer or array structure. In the context of Excel, this typically manifests through the parsing and rendering of complex spreadsheet files containing specially crafted formulas, embedded objects, or malformed XML structures. When an attacker constructs a malicious document designed to exploit this specific logic error in the application's codebase, they can trigger the out-of-bounds read condition during file processing. The significance of this flaw lies not merely in its potential for data leakage but in its capability to facilitate remote code execution under certain conditions or configurations where subsequent memory corruption techniques are chained with the initial information disclosure.
From a technical perspective, an out-of-bounds read is categorized under CWE-125, which defines it as accessing memory beyond the end of a buffer without writing to that location. While traditionally viewed primarily as an information disclosure vulnerability, in modern exploit development methodologies, such reads are frequently utilized as primitive steps for more severe attacks. By reading arbitrary memory contents, an attacker may gain insights into the application's internal state, including stack canaries, function pointers, or other security mitigations employed by Microsoft Office. This intelligence allows the adversary to bypass protections like Data Execution Prevention (DEP) and Address Space Layout Randomization (ASLR), thereby paving the way for arbitrary code execution. The vulnerability is particularly dangerous because it affects a widely used productivity tool that processes documents received via email, shared drives, or web downloads, making it an attractive target for phishing campaigns and drive-by download attacks.
The operational impact of this vulnerability extends beyond individual system compromise to potential organizational-wide risks due to the network-based nature of the attack vector. Since Excel is often integrated with cloud services and collaborative platforms, a malicious file can be distributed rapidly across corporate networks. Successful exploitation could lead to unauthorized access to sensitive data stored on the victim's machine, installation of malware such as ransomware or remote access trojans, and complete loss of system integrity. The ability for an attacker to execute code over a network implies that no physical interaction with the target is required beyond opening the malicious file in Excel, significantly lowering the barrier to entry for adversaries. This aligns with ATT&CK technique T1203, which covers exploitation for client execution, highlighting how attackers leverage vulnerabilities in software applications commonly used by end-users to gain an initial foothold within a network environment.
Mitigation strategies must focus on both immediate remediation and long-term defensive posture improvements. The primary defense is the timely application of security updates provided by Microsoft through Windows Update or the Office update channel. Organizations should ensure that all endpoints running affected versions of Excel are patched immediately upon release of the relevant security bulletin. In addition to patching, implementing Application Control policies such as those found in Windows Defender Application Control can prevent untrusted applications from executing code, thereby neutralizing the payload delivered by the exploit. Furthermore, restricting macro execution and disabling automatic content loading for files received from external sources reduces the attack surface significantly. Security awareness training is also crucial, as user interaction with suspicious attachments remains a common initial access vector. Regular auditing of installed software versions and enforcing least privilege principles where users operate without administrative rights can further limit the potential impact if an exploit attempt succeeds.