CVE-2026-70105 in Office
Summary
by MITRE • 08/21/2026
Improper input validation in Microsoft Office Word allows an unauthorized attacker to disclose information over a network.
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Analysis
by VulDB Data Team • 08/21/2026
The vulnerability described involves a critical flaw within the document processing engine of Microsoft Office Word, specifically stemming from improper input validation mechanisms. This security weakness arises when the application fails to adequately sanitize or verify data structures and file formats before parsing them for rendering or execution. In complex office documents such as those created in .docx format, numerous embedded objects, macros, metadata fields, and formatting instructions are processed by various subsystems within Word. When these inputs contain malformed or unexpectedly structured data, the lack of rigorous validation allows an attacker to manipulate how the application interprets specific elements. This manipulation does not necessarily lead to arbitrary code execution in this instance but is instead leveraged to trigger unintended information disclosure behaviors within the software stack.
From a technical perspective, improper input validation often manifests as buffer over-reads or logic errors where the application reads beyond allocated memory boundaries or accesses sensitive internal states that should remain isolated from external inputs. In the context of Microsoft Office Word, an attacker can craft a malicious document containing specially designed content that exploits these validation gaps. When a victim opens this crafted file, the vulnerability is triggered during the parsing phase. The flaw allows the application to expose internal memory contents or system information that was not intended for public view. This could include sensitive data stored in temporary files, clipboard history, or other contextual information residing on the user's machine. The attack vector typically relies on social engineering tactics where the victim is persuaded to open a seemingly legitimate but maliciously crafted document via email attachments or file sharing services.
The operational impact of this vulnerability centers on confidentiality rather than integrity or availability. By disclosing internal system information, an attacker gains valuable intelligence that can facilitate further attacks. This disclosed data might reveal details about the operating system version, installed software configurations, network topology hints, or user-specific identifiers. Such reconnaissance is a foundational step in advanced persistent threat campaigns and targeted espionage operations. The ability to exfiltrate this information over a network means that once triggered, the attacker can remotely collect sensitive context without needing direct access to the victim's file system or administrative privileges on the host machine. This significantly lowers the barrier for subsequent exploitation phases, as the attacker now possesses detailed knowledge of the target environment.
This vulnerability aligns with Common Weakness Enumeration category CWE-20 Improper Input Validation and potentially CWE-200 Exposure of Sensitive Information to an Unauthorized Actor. In terms of offensive security frameworks, it maps to MITRE ATT&CK techniques related to Collection such as Data from Local System or Screen Capture if the disclosure involves visual elements, though primarily it falls under reconnaissance activities that support later stages like Credential Access or Lateral Movement depending on what specific data is leaked. The exploitation relies heavily on user interaction, classifying it within social engineering vectors where trust in file sources is exploited to bypass perimeter defenses.
Mitigation strategies for this vulnerability require a multi-layered approach focusing on both technical controls and user awareness. Organizations should ensure that Microsoft Office applications are updated with the latest security patches released by Microsoft, as these updates typically contain specific fixes for input validation logic within the document parsers. Network segmentation can help limit the impact if an endpoint is compromised by restricting outbound connections to only necessary destinations, thereby reducing the effectiveness of data exfiltration attempts. Additionally, deploying advanced email gateways and anti-malware solutions that inspect documents in sandboxed environments before delivery to end-users can detect and block malicious files containing known exploit patterns. User training remains critical; employees should be educated to verify the source of unexpected attachments and avoid opening documents from untrusted senders. Enabling Protected View for all downloaded or opened-from-internet files provides an additional layer of isolation, preventing potentially harmful content from executing in a trusted context until manually approved by the user.