CVE-2026-40367: Microsoft Office Word Untrusted Pointer Dereference Vulnerability

CVE-2026-40367 is an untrusted pointer dereference vulnerability affecting Microsoft Office Word. This vulnerability enables an unauthorized attacker to execute arbitrary code locally on a vulnerable system. The vulnerability stems from improper handling of memory pointers within the application, leading to a situation where a maliciously crafted document can trigger the dereference of an untrusted pointer. Successful exploitation allows attackers to gain control over the affected system, potentially leading to data theft, malware installation, or further unauthorized activities. This vulnerability poses a significant risk to organizations and individuals using Microsoft Office Word, as it can be exploited through social engineering tactics, such as distributing malicious documents via email or other communication channels.

Attack Chain

1. An attacker crafts a malicious Word document designed to trigger the untrusted pointer dereference vulnerability (CVE-2026-40367).
2. The attacker distributes the malicious document to a target user via email, shared network drive, or other means.
3. The target user opens the malicious document in Microsoft Office Word.
4. Upon opening the document, the vulnerable code path is triggered, causing the application to attempt to dereference an untrusted pointer.
5. The untrusted pointer dereference leads to the execution of arbitrary code within the context of the Word process.
6. The attacker leverages the code execution to install malware, establish persistence, or perform other malicious activities on the compromised system.
7. The attacker may attempt to escalate privileges or move laterally within the network, depending on the initial access level.

Impact

Successful exploitation of CVE-2026-40367 allows an attacker to execute arbitrary code on a target system with the privileges of the user running Microsoft Office Word. This can lead to complete system compromise, including data theft, malware installation, and denial of service. Given the widespread use of Microsoft Office Word, this vulnerability has the potential to affect a large number of users and organizations. If successful, an attacker could gain a foothold within an organization’s network and use it as a launching point for further attacks.

Recommendation

• Apply the security update released by Microsoft to patch CVE-2026-40367 as soon as possible.
• Deploy the provided Sigma rule to detect potential exploitation attempts targeting CVE-2026-40367.
• Educate users on the risks of opening documents from untrusted sources to mitigate the risk of social engineering attacks.
• Monitor process creation events for unusual or suspicious processes spawned by Microsoft Word, as indicated in the Sigma rule.