CVE-2025-32717: Microsoft 365 Apps Buffer Overflow Flaw

CVE-2025-32717 Overview

CVE-2025-32717 is a heap-based buffer overflow vulnerability [CWE-122] in Microsoft Office Word that allows an unauthorized attacker to execute arbitrary code locally. The flaw affects Microsoft 365 Apps for Enterprise and triggers when Word parses a specially crafted document. Successful exploitation grants the attacker code execution in the context of the current user, with high impact on confidentiality, integrity, and availability. Microsoft published the advisory on June 11, 2025, and the issue carries a CVSS 3.1 base score of 8.4. No public proof-of-concept code or in-the-wild exploitation has been observed at the time of writing.

Critical Impact

An attacker who convinces a user to open a malicious Word document can execute arbitrary code on the target system, with no authentication or user interaction beyond opening the file.

Affected Products

• Microsoft 365 Apps for Enterprise (Word component)
• Microsoft Office Word desktop client distributions tied to 365 Apps
• Endpoints running unpatched Microsoft 365 Apps installations

Discovery Timeline

• 2025-06-11 - CVE-2025-32717 published to NVD
• 2025-06-11 - Microsoft Security Update CVE-2025-32717 released
• 2025-07-09 - Last updated in NVD database

Technical Details for CVE-2025-32717

Vulnerability Analysis

The vulnerability is a heap-based buffer overflow [CWE-122] in Microsoft Office Word. Word allocates a heap buffer to hold data parsed from a document structure, then writes attacker-controlled content past the allocated bounds. The overflow corrupts adjacent heap metadata or object data, which an attacker can shape to redirect control flow.

The attack vector is local, meaning the malicious payload arrives as a file the victim opens. Microsoft's advisory categorizes the issue as enabling code execution without authentication. Because Word runs in the context of the logged-on user, successful exploitation inherits that user's privileges. On systems where the user holds administrative rights, the attacker gains full control of the host.

Root Cause

The root cause is improper validation of the size of input data copied into a heap-allocated buffer during document parsing. Word fails to verify that the source length fits the destination allocation before performing the copy operation. This classic boundary check failure permits adjacent heap memory corruption.

Attack Vector

The attacker delivers a weaponized .docx, .doc, or .rtf file through phishing email, a shared drive, or a drive-by download. When the target opens the document in a vulnerable build of Word, the parser triggers the overflow. Preview Pane handling can broaden the exposure on some configurations. The vulnerability requires no privileges and no separate user interaction beyond opening the document.

No public proof-of-concept code is currently available. Detailed exploitation mechanics have not been disclosed by Microsoft beyond the advisory text. See the Microsoft Security Update CVE-2025-32717 for vendor-supplied details.

Detection Methods for CVE-2025-32717

Indicators of Compromise

• WINWORD.EXE spawning unexpected child processes such as cmd.exe, powershell.exe, rundll32.exe, or mshta.exe
• Crash events or Windows Error Reporting entries referencing winword.exe with heap corruption faults (for example c0000374)
• Office documents arriving from external senders containing unusual embedded objects, OLE streams, or malformed structures
• Outbound network connections initiated by WINWORD.EXE to previously unseen domains or IP addresses

Detection Strategies

• Hunt for process lineage where WINWORD.EXE is the parent of script interpreters, LOLBins, or shell processes
• Monitor for Office applications writing executable content to %TEMP%, %APPDATA%, or startup paths
• Apply Microsoft Defender Attack Surface Reduction (ASR) rules that block Office from creating child processes and from injecting code
• Correlate Word crash telemetry with subsequent suspicious activity on the same host within a short time window

Monitoring Recommendations

• Enable command-line and module-load auditing on endpoints running Microsoft 365 Apps
• Forward Sysmon process creation, image load, and file create events to a centralized analytics platform
• Track Office telemetry for repeated crashes that may indicate exploitation attempts or fuzzing
• Alert on inbound email attachments with Office macros, embedded OLE objects, or RTF content from external senders

How to Mitigate CVE-2025-32717

Immediate Actions Required

• Apply the Microsoft security update referenced in the Microsoft Security Update CVE-2025-32717 advisory across all Microsoft 365 Apps installations
• Verify that Microsoft 365 Apps update channels are configured to receive current builds and confirm patch deployment status from the management console
• Enforce Protected View and Block Macros from Internet for all Office applications via Group Policy
• Restrict end-user local administrative rights to limit the impact of successful exploitation

Patch Information

Microsoft released a security update for Microsoft 365 Apps addressing CVE-2025-32717 on June 11, 2025. Administrators should consult the Microsoft Security Update CVE-2025-32717 page for the specific build numbers per update channel (Current Channel, Monthly Enterprise Channel, Semi-Annual Enterprise Channel). Confirm installed Office build using File > Account > About Word and compare against the fixed version listed in the advisory.

Workarounds

• Disable the Outlook Reading Pane and Windows Explorer Preview Pane to reduce passive triggering of document parsing
• Configure File Block policy to prevent opening of legacy Word formats from untrusted locations
• Open documents from untrusted sources only in Office for the web or Application Guard for Office
• Use email gateway controls to strip or sandbox Office attachments originating outside the organization

# Configuration example: enforce Protected View via registry on Windows endpoints
reg add "HKCU\Software\Microsoft\Office\16.0\Word\Security\ProtectedView" /v DisableAttachmentsInPV /t REG_DWORD /d 0 /f
reg add "HKCU\Software\Microsoft\Office\16.0\Word\Security\ProtectedView" /v DisableInternetFilesInPV /t REG_DWORD /d 0 /f
reg add "HKCU\Software\Microsoft\Office\16.0\Word\Security\ProtectedView" /v DisableUnsafeLocationsInPV /t REG_DWORD /d 0 /f

# Block macros from the internet
reg add "HKCU\Software\Microsoft\Office\16.0\Word\Security" /v BlockContentExecutionFromInternet /t REG_DWORD /d 1 /f