CVE-2025-53731: Microsoft 365 Apps Use-After-Free Flaw

CVE-2025-53731 Overview

CVE-2025-53731 is a use-after-free vulnerability [CWE-416] in Microsoft Office that enables local code execution. An attacker who successfully exploits this flaw can run arbitrary code in the context of the current user. The issue affects multiple Office product families, including Microsoft 365 Apps, Microsoft Office 2016 and 2019, and Office Long Term Servicing Channel (LTSC) 2021 and 2024 on both Windows and macOS.

The attack vector is local, but no authentication or user interaction is required by the vulnerable component once a crafted document is processed. Microsoft published a security advisory addressing the issue in the August 2025 security update cycle.

Critical Impact
Successful exploitation results in arbitrary code execution with the privileges of the user running Microsoft Office, enabling full compromise of confidentiality, integrity, and availability on the host.

Affected Products

Microsoft 365 Apps (Enterprise, x64 and x86)
Microsoft Office 2016 and Microsoft Office 2019 (x64 and x86)
Microsoft Office LTSC 2021 and 2024 (Windows x64/x86 and macOS)

Discovery Timeline

2025-08-12 - CVE-2025-53731 published to NVD
2025-08-12 - Microsoft releases security update for CVE-2025-53731
2025-08-15 - Last updated in NVD database

Technical Details for CVE-2025-53731

Vulnerability Analysis

The flaw is a use-after-free condition in Microsoft Office. Use-after-free vulnerabilities occur when a program continues to reference memory after it has been freed. An attacker who controls the contents of the reallocated memory region can redirect execution to attacker-controlled data.

In the Office context, this typically involves a crafted document, such as a Word, Excel, or RTF file, that triggers anomalous object lifetime handling inside the application. When the freed object is reaccessed, the application dereferences a dangling pointer to memory the attacker has reshaped.

Microsoft classifies the attack vector as local, meaning the vulnerable code path is reached when a user opens or previews a malicious file on the target system. The scope is unchanged, and impact to confidentiality, integrity, and availability is high.

Root Cause

The root cause is improper management of an object's lifetime within Office's document parsing or rendering logic. A reference to an object remains usable after the underlying memory is released. The attacker grooms the heap so that the freed allocation is replaced with controlled data before the dangling reference is consumed.

Attack Vector

An attacker delivers a malicious Office document through email, file share, web download, or other delivery channels. When the file is rendered, the use-after-free is triggered and the attacker gains code execution as the current user. Microsoft's advisory does not list a public proof-of-concept, and CISA KEV does not currently list this CVE.

No verified exploit code is publicly available for CVE-2025-53731. Refer to the Microsoft Security Update CVE-2025-53731 advisory for vendor technical details.

Detection Methods for CVE-2025-53731

Indicators of Compromise

Unexpected child processes spawned by winword.exe, excel.exe, powerpnt.exe, or outlook.exe, especially cmd.exe, powershell.exe, mshta.exe, or rundll32.exe.
Office processes writing executable content to %TEMP%, %APPDATA%, or user profile directories.
Crash events (Application Error 1000) referencing Office binaries with access violations consistent with use-after-free conditions.
Outbound network connections initiated directly by Office processes to non-Microsoft destinations.

Detection Strategies

Hunt for parent-child process relationships where Office binaries spawn scripting or living-off-the-land binaries.
Inspect inbound email attachments and shared files for Office documents containing embedded objects, OLE controls, or unusual structured storage streams.
Monitor for in-memory anomalies in Office processes such as new RWX regions or reflective loads.
Correlate Office crash telemetry with subsequent suspicious activity on the same endpoint.

Monitoring Recommendations

Enable PowerShell script block logging, command-line process auditing, and Sysmon (event IDs 1, 7, 10, 11) on endpoints running Office.
Forward Office crash and Application Error events to a central log platform for retrospective hunting.
Track patch deployment status for Microsoft 365 Apps and Office LTSC builds released alongside the August 2025 security updates.

How to Mitigate CVE-2025-53731

Immediate Actions Required

Apply Microsoft's August 2025 security updates for all affected Office and Microsoft 365 Apps channels without delay.
Identify endpoints running unsupported or unpatched Office builds and prioritize them for remediation.
Restrict execution of untrusted Office documents from email and external file shares pending patch rollout.

Patch Information

Microsoft addressed CVE-2025-53731 in the August 2025 Patch Tuesday cycle. Update paths and build numbers for each affected product are listed in the Microsoft Security Update CVE-2025-53731 advisory. Microsoft 365 Apps customers receive the fix through the standard Click-to-Run update channel, while perpetual-license Office 2016, 2019, and LTSC builds require the corresponding monthly security update package.

Workarounds

Enable Protected View and Application Guard for Office to isolate documents originating from the internet or email.
Block macros from running in Office files from the internet using the Microsoft-published Group Policy setting.
Configure Attack Surface Reduction (ASR) rules that block Office applications from creating child processes and from injecting code into other processes.
Use email gateway controls to strip or sandbox Office attachments from untrusted senders until patches are fully deployed.

bash

# Example: enable key Attack Surface Reduction rules via PowerShell
Set-MpPreference -AttackSurfaceReductionRules_Ids `
  D4F940AB-401B-4EFC-AADC-AD5F3C50688A, `
  3B576869-A4EC-4529-8536-B80A7769E899, `
  75668C1F-73B5-4CF0-BB93-3ECF5CB7CC84 `
  -AttackSurfaceReductionRules_Actions Enabled, Enabled, Enabled