CVE-2025-53732: Microsoft 365 Copilot Buffer Overflow Flaw

CVE-2025-53732 Overview

CVE-2025-53732 is a heap-based buffer overflow in Microsoft Office that enables local code execution. The flaw is tracked under CWE-122 (Heap-based Buffer Overflow) and CWE-787 (Out-of-bounds Write). Exploitation requires a user to open a crafted document, after which the attacker runs code in the context of the current user. Microsoft published the advisory on August 12, 2025 and rates the issue Important. Affected products include Microsoft Office and Microsoft 365 Copilot. See the Microsoft CVE-2025-53732 Advisory for vendor guidance.

Critical Impact
A successful attack yields arbitrary code execution with the victim user's privileges, enabling credential theft, lateral movement, and payload staging.

Affected Products

Microsoft Office (universal)
Microsoft 365 Copilot (Android)
Documents opened in Office desktop and mobile clients exposing the vulnerable parser

Discovery Timeline

2025-08-12 - CVE-2025-53732 published to the National Vulnerability Database
2025-08-12 - Microsoft releases security update via MSRC
2026-05-22 - Last updated in NVD database

Technical Details for CVE-2025-53732

Vulnerability Analysis

The vulnerability is a heap-based buffer overflow inside Microsoft Office document parsing code. When Office processes a malformed structure within a document, it writes past the bounds of a heap-allocated buffer. The out-of-bounds write corrupts adjacent heap metadata or object pointers. An attacker who controls the overflowed data can steer execution toward attacker-supplied code.

Exploitation is local and requires user interaction. The victim opens a weaponized Office file delivered through email, chat, or a web download. No prior authentication or elevated privileges are required on the target system. Successful exploitation grants the attacker the same rights as the logged-on user, including read and write access to user data and the ability to launch follow-on processes.

Microsoft 365 Copilot is listed as affected on Android, reflecting the shared Office document processing components used by the mobile experience. The issue impacts confidentiality, integrity, and availability of the affected host.

Root Cause

The root cause is improper validation of an input length or structure size during document parsing. The code calculates a destination buffer size that is smaller than the attacker-controlled source data and then performs a copy. Because the allocation lives on the heap, the resulting corruption can overwrite adjacent objects, virtual function pointers, or allocator control structures.

Attack Vector

The attack vector is local with required user interaction. A typical chain begins with a phishing email carrying a malicious Office attachment or a link to a remote document. When the user opens the file, the vulnerable parser processes the crafted object and triggers the overflow. Attackers commonly pair such flaws with heap grooming and ROP-style payloads to bypass exploit mitigations and reach shellcode.

No verified public exploit code is available. See the Microsoft CVE-2025-53732 Advisory for the authoritative technical description.

Detection Methods for CVE-2025-53732

Indicators of Compromise

Office applications (WINWORD.EXE, EXCEL.EXE, POWERPNT.EXE) spawning shells such as cmd.exe, powershell.exe, or wscript.exe
Unexpected child processes of Office writing executables to %APPDATA%, %TEMP%, or %PUBLIC%
Office processes initiating outbound network connections to non-Microsoft infrastructure shortly after a document is opened
Crash telemetry from Office binaries with heap corruption signatures in Windows Error Reporting

Detection Strategies

Hunt for parent-child process anomalies where Office binaries launch scripting hosts or LOLBins
Inspect documents with embedded objects, unusual OLE streams, or oversized structures using static analysis tooling
Correlate Office crashes with subsequent process creation events to surface exploitation attempts

Monitoring Recommendations

Forward Office, Sysmon, and EDR telemetry to a centralized analytics platform for behavioral correlation
Alert on Office macro execution combined with network egress or file write events
Track patch deployment status across endpoints to identify hosts still exposed to CVE-2025-53732

How to Mitigate CVE-2025-53732

Immediate Actions Required

Apply the August 2025 Microsoft Office security updates referenced in the MSRC advisory to every affected endpoint
Update Microsoft 365 Copilot on Android through the Google Play Store to the latest available version
Block inbound Office attachments from untrusted external senders at the mail gateway until patching completes
Enable Protected View and Application Guard for Office on managed endpoints

Patch Information

Microsoft addressed CVE-2025-53732 in the security update published on August 12, 2025. Administrators should deploy the update through Microsoft Update, Windows Server Update Services (WSUS), Microsoft Intune, or the Microsoft 365 Apps update channel. Verify the installed Click-to-Run or MSI build number against the fixed version listed in the MSRC advisory.

Workarounds

Configure Office to open documents from the internet in Protected View and disable editing by default
Enable Attack Surface Reduction (ASR) rules that block Office applications from creating child processes and injecting into other processes
Restrict execution of Office macros from internet-sourced files through Group Policy

bash

# Example: enable ASR rule blocking Office child processes via PowerShell
Add-MpPreference -AttackSurfaceReductionRules_Ids D4F940AB-401B-4EFC-AADC-AD5F3C50688A `
                 -AttackSurfaceReductionRules_Actions Enabled