CVE-2026-108433 in Office
Summary
by MITRE • 10/16/2026
Reliance on untrusted inputs in a security decision in Microsoft Office Word allows an unauthorized attacker to bypass a security feature locally.
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Analysis
by VulDB Data Team • 10/16/2026
The vulnerability described involves a critical flaw within the Microsoft Office Word application, specifically categorized as a reliance on untrusted inputs during a security decision process. This type of defect typically falls under CWE-20 Improper Input Validation or CWE-798 Use of Hard-coded Credentials if the bypass relates to authentication mechanisms, but in the context of local privilege escalation via document processing, it is most closely aligned with CWE-434 Unrestricted Upload of File with Dangerous Type when considering file handling aspects. The core issue arises because Word fails to adequately sanitize or validate inputs derived from external sources before making internal security decisions regarding how those inputs are processed. An attacker who can trick a user into opening a specially crafted document can exploit this lack of validation to manipulate the application's behavior in unintended ways, effectively bypassing built-in security controls designed to prevent malicious code execution or unauthorized system access.
From an operational perspective, this vulnerability allows for local exploitation by an unauthorized attacker with limited privileges. The attack vector generally involves social engineering tactics where a victim is persuaded to open a maliciously constructed Word document containing embedded objects, macros, or specific formatting that triggers the flawed security logic. Once executed within the context of the user's session, the application may perform actions such as loading arbitrary libraries, executing system commands, or modifying registry keys without proper authorization checks. This bypasses features like Protected View or macro security settings which are intended to isolate potentially harmful content from the rest of the operating system. The impact is significant because it can lead to full compromise of the user's account and potentially the underlying host machine if further exploitation steps follow, such as privilege escalation techniques leveraging other local vulnerabilities.
In terms of industry standards mapping, this vulnerability aligns with MITRE ATT&CK technique T1204 User Execution, where an attacker relies on a victim to perform actions that lead to code execution. It also relates to T1059 Command and Scripting Interpreter if the bypass allows for script-based attacks within Office applications. The failure to validate inputs against expected formats or trust boundaries represents a fundamental design flaw in how security policies are enforced during runtime operations involving external data sources. This highlights the importance of implementing strict allow-listing strategies rather than relying on block-lists which can be easily circumvented through obfuscation techniques commonly used by threat actors.
Mitigation for this vulnerability primarily involves applying the latest cumulative updates and patches released by Microsoft to address the specific code path responsible for the input validation failure. Organizations should enforce application control policies such as AppLocker or Windows Defender Application Control to restrict the execution of untrusted scripts and binaries, thereby limiting the impact even if a user inadvertently triggers the exploit. Additionally, enabling Enhanced Security Configuration in Office applications can help mitigate risks by disabling active content like macros from internet-sourced files by default. User awareness training is also crucial to reduce the likelihood of successful social engineering attempts that serve as the initial delivery mechanism for this type of local exploitation. Regular monitoring and logging of suspicious process creations or file modifications within Word instances can aid in early detection of attempted exploits before they result in full system compromise.