CVE-2025-29791 in Excel
Summary
by MITRE • 04/08/2025
Access of resource using incompatible type ('type confusion') in Microsoft Office allows an unauthorized attacker to execute code locally.
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Analysis
by VulDB Data Team • 04/09/2025
Type confusion vulnerabilities represent a critical class of software defects that occur when a program uses a resource with an inappropriate data type, often leading to memory corruption and potential code execution. In the context of Microsoft Office applications, this specific vulnerability arises from improper handling of object types during processing of maliciously crafted Office documents. The flaw typically manifests when the application fails to properly validate or distinguish between different data types, allowing an attacker to manipulate memory structures through carefully constructed input that appears legitimate but contains malicious payloads designed to exploit type confusion patterns.
The technical implementation of this vulnerability involves scenarios where Microsoft Office components process external data without adequate type checking mechanisms. When parsing structured document formats such as docx, xlsx, or pptx files, the application may encounter unexpected data sequences that trigger incorrect type assumptions within the memory management system. This misalignment between expected and actual data types creates opportunities for attackers to overwrite critical memory locations, manipulate execution flow, or inject malicious code into the target system. The vulnerability often exploits weaknesses in object-oriented programming patterns where objects are reused or reinterpreted without proper validation of their current type state.
From an operational perspective, successful exploitation of this type confusion vulnerability can result in arbitrary code execution with the privileges of the affected user, typically leading to complete system compromise. Attackers commonly deliver malicious Office documents through phishing campaigns, exploit kits, or compromised websites where users inadvertently open infected files. The local execution aspect means that successful exploitation does not require network connectivity post-initial compromise, as the vulnerability enables direct manipulation of the target machine's memory space. This makes the attack vector particularly dangerous in enterprise environments where users frequently open documents from untrusted sources.
Security professionals should implement multiple layers of defense to protect against this vulnerability class. Microsoft regularly releases security updates and patches that address specific type confusion flaws in Office applications, making timely patch management critical for mitigation. Network segmentation and email filtering solutions can help prevent initial delivery of malicious documents, while user education regarding suspicious file attachments remains essential. The vulnerability aligns with several attack patterns documented in the mitre att&ck framework under techniques such as 'exploitation for execution' and 'valid accounts', emphasizing the importance of least privilege principles and monitoring for unusual process behavior that might indicate exploitation attempts.
Organizations should also consider implementing application whitelisting policies that restrict execution of unauthorized Office macros or external content, alongside regular security assessments to identify potential type confusion vulnerabilities in custom applications. The underlying CWE classification for this vulnerability falls under CWE-471, which specifically addresses 'Use of Inappropriate Resource Type', making it a direct descendant of broader software quality and memory safety concerns. Proper input validation, defensive programming practices, and rigorous code review processes are essential to prevent such vulnerabilities from manifesting in production systems, particularly in applications that process complex external data formats like Microsoft Office documents.