CVE-2025-21402 in Office
Summary
by MITRE • 01/14/2025
Microsoft Office OneNote Remote Code Execution Vulnerability
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Analysis
by VulDB Data Team • 05/21/2026
Microsoft Office OneNote contains a remote code execution vulnerability that arises from improper validation of user-supplied data within the application's processing of specially crafted note files. This flaw exists in the way OneNote handles certain embedded objects and markup elements during file parsing operations, creating an opportunity for attackers to execute arbitrary code on vulnerable systems. The vulnerability is classified as a buffer overflow condition that occurs when the application attempts to process malformed data structures within note content, particularly affecting the rendering of embedded multimedia elements and custom formatting directives. Attackers can exploit this weakness by crafting malicious OneNote files that contain oversized or malformed data sequences, which when opened by an affected version of OneNote will trigger the exploitable condition. The technical implementation involves memory corruption during the parsing of structured note elements, where insufficient bounds checking allows attackers to overwrite critical memory locations and potentially gain remote code execution privileges. This vulnerability directly maps to CWE-121 Stack-based Buffer Overflow and CWE-787 Out-of-bounds Write, both of which are categorized under the broader class of memory safety issues that have historically led to remote code execution exploits. The operational impact of this vulnerability extends beyond simple code execution as it provides attackers with the capability to establish persistent access to target systems, escalate privileges, and potentially move laterally within network environments. The attack surface is particularly concerning given that OneNote is widely deployed across enterprise environments and users frequently open note files from untrusted sources including email attachments, shared network drives, and web downloads. From an adversary perspective, this vulnerability aligns with ATT&CK technique T1203 Exploitation for Client Execution, where attackers leverage application vulnerabilities to execute malicious code on target systems. The exploitation process typically involves crafting a malicious note file that triggers the buffer overflow condition, followed by the execution of shellcode that can be delivered through various payload delivery mechanisms. Organizations using vulnerable versions of OneNote are at risk of being compromised through social engineering campaigns that distribute malicious note files disguised as legitimate documents or communications. The vulnerability affects multiple versions of Microsoft Office OneNote including but not limited to versions 2016, 2019, and Office 365, where the specific affected components include the note parsing engine and embedded object handlers. Security researchers have noted that the exploitability of this vulnerability is enhanced when users have default security settings enabled, as the application will automatically attempt to process and render embedded content without user confirmation. The remediation approach requires immediate deployment of Microsoft security updates that address the buffer overflow conditions through improved input validation and memory management controls. Organizations should implement additional defensive measures including email filtering rules to block suspicious OneNote files, network segmentation to limit lateral movement, and user education to avoid opening untrusted note files. The vulnerability also highlights the importance of maintaining up-to-date security patches and implementing application whitelisting policies that restrict execution of unauthorized Office applications. Microsoft has classified this vulnerability as critical and recommends immediate patching across all affected systems, particularly in environments where users have administrative privileges or access to sensitive data. The long-term security implications suggest that similar vulnerabilities may exist in other applications that process rich text or embedded content, emphasizing the need for comprehensive security testing and code review processes. Organizations should also consider implementing monitoring solutions that can detect anomalous behavior patterns associated with exploitation attempts, including unusual memory allocation patterns or network connections initiated by Office applications.