CVE-2025-29816 in Word
Summary
by MITRE • 04/08/2025
Improper input validation in Microsoft Office Word allows an unauthorized attacker to bypass a security feature over a network.
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Analysis
by VulDB Data Team • 09/09/2026
The vulnerability described involves improper input validation within the core processing engine of Microsoft Office Word, specifically affecting how the application handles data received from external sources or embedded objects. This flaw represents a fundamental breakdown in the principle of least privilege and secure coding practices, where the software fails to adequately sanitize or verify user-supplied input before it is processed by internal functions. In many instances, such vulnerabilities arise when an attacker crafts maliciously formatted documents that exploit edge cases in how Word parses complex file structures, macros, or embedded ActiveX controls. The lack of rigorous validation allows data that should be rejected as invalid to pass through initial security checks and enter deeper layers of the application's execution environment. This bypass is particularly dangerous because it circumvents built-in protections designed to isolate untrusted content from critical system resources, effectively allowing an unauthorized actor to execute arbitrary code or manipulate application state without triggering standard warning dialogs or sandbox restrictions.
From a technical perspective, this type of vulnerability often falls under the category of CWE-20 Improper Input Validation and may leverage mechanisms similar to those identified in ATT&CK technique T1566.001 Phishing: Spearphishing Attachment. The operational impact is severe, as it enables remote code execution on affected systems without requiring physical access or prior authentication beyond opening the malicious document. An attacker can distribute these crafted files via email attachments, shared network drives, or web downloads. When a victim opens the file, the improperly validated input triggers specific routines within Word that execute commands with the privileges of the current user. This can lead to full system compromise if the user has administrative rights, allowing for data exfiltration, installation of persistent backdoors, lateral movement across corporate networks, and potential disruption of business operations. The ability to bypass security features means that traditional perimeter defenses may not detect or block these attacks until significant damage has occurred.
Mitigation strategies must address both immediate remediation and long-term architectural improvements. Organizations should immediately apply the latest cumulative updates provided by Microsoft, which typically include patches for such input validation flaws in Office components. It is critical to ensure that all endpoints are running supported versions of Windows and Office with automatic update mechanisms enabled to reduce exposure windows. Additionally, implementing application control policies using tools like AppLocker or Windows Defender Application Control can restrict the execution of untrusted scripts and binaries generated by Word documents. Security awareness training for end-users remains essential to prevent social engineering tactics that rely on tricking users into opening suspicious attachments. Furthermore, deploying advanced email gateways with sandboxing capabilities can analyze incoming documents in isolated environments before they reach user mailboxes, detecting and blocking malicious payloads based on behavioral analysis rather than just signature matching. Regular vulnerability assessments and penetration testing should also be conducted to identify similar input handling weaknesses across the enterprise software stack.