CVE-2026-108434 in Office
Summary
by MITRE • 10/16/2026
Out-of-bounds read in Microsoft Office Word allows an unauthorized attacker to disclose information over a network.
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Analysis
by VulDB Data Team • 10/16/2026
The vulnerability described constitutes a critical security flaw within the document parsing engine of Microsoft Office Word, specifically manifesting as an out-of-bounds read condition. This type of memory corruption error occurs when the application attempts to access data at a memory location that is outside the boundaries of the intended buffer or array structure. In the context of word processing software, this typically happens during the rendering or parsing of complex document elements such as embedded objects, specific formatting codes, or malformed XML structures within .docx files. When an attacker crafts a malicious Word document containing specially constructed data fields that trigger this boundary violation, the application fails to properly validate the length and offset parameters before reading from memory. This lack of rigorous input validation allows the program to retrieve sensitive information stored in adjacent memory regions, which may contain stack variables, heap metadata, or other process-specific data that was not intended for disclosure.
From a technical perspective, this flaw aligns with Common Weakness Enumeration (CWE) category CWE-125, Out-of-bounds Read, and is often associated with improper input validation as defined by CWE-20. The operational impact of such a vulnerability extends beyond simple data leakage; while the primary description highlights information disclosure over a network, out-of-bands reads can frequently serve as precursors to more severe exploits. By carefully controlling the memory layout through repeated exploitation attempts or specific document structures, an attacker might be able to leak pointers that facilitate further attacks, including remote code execution via heap spraying techniques or use-after-free scenarios. The ability to disclose information over a network implies that this vulnerability can be triggered remotely if the malicious document is delivered via email attachments, shared drives, or web-based access points like SharePoint Online, thereby increasing the attack surface significantly without requiring user interaction beyond opening the file in certain automated viewing contexts.
The presence of this flaw indicates a gap in the defensive mechanisms employed by Microsoft Office Word during the processing of untrusted input. Modern office suites employ various sandboxing and isolation techniques to mitigate such risks, but low-level memory errors like out-of-bounds reads often bypass these higher-level protections if they occur within core rendering libraries that operate with elevated privileges or direct access to system resources. This vulnerability is particularly dangerous because it can be exploited by adversaries seeking to conduct reconnaissance on a target organization's systems. By extracting internal IP addresses, user session tokens, or cryptographic keys stored in memory, attackers gain valuable intelligence that aids in subsequent phases of an attack campaign as outlined in the MITRE ATT&CK framework, specifically under techniques related to Credential Access and Discovery such as T1005 (Data from Local System) or T1074 (Data Staged).
To mitigate this risk, organizations must ensure that all Microsoft Office installations are updated with the latest security patches released by Microsoft. These updates typically include fixes for memory safety checks and improved validation logic within the document parsing components. Administrators should also enforce strict email filtering policies to block attachments from unknown senders and disable automatic content loading in Word documents where possible, forcing users to explicitly enable editing or viewing of potentially unsafe elements. Additionally, deploying endpoint detection and response solutions that monitor for anomalous memory access patterns can help detect exploitation attempts in real-time. Long-term mitigation strategies should involve adopting secure coding practices within the software development lifecycle, emphasizing rigorous static analysis and fuzzing testing specifically targeting document parsing engines to identify and remediate boundary validation errors before they reach production environments.