CVE-2025-53740: Microsoft 365 Apps Use After Free Flaw

CVE-2025-53740 Overview

CVE-2025-53740 is a use-after-free vulnerability in Microsoft Office that allows an unauthorized attacker to execute arbitrary code locally. The flaw is tracked under CWE-416 and affects multiple Microsoft Office distributions, including Microsoft 365 Apps, Office 2016, Office 2019, and Office Long Term Servicing Channel 2021 and 2024. Successful exploitation can yield full compromise of confidentiality, integrity, and availability on the affected host. Microsoft published the advisory on August 12, 2025, and no public proof-of-concept code or in-the-wild exploitation has been reported at the time of writing.

Critical Impact
An attacker who successfully exploits CVE-2025-53740 can execute arbitrary code in the context of the current user, leading to full host compromise without requiring authentication or user interaction.

Affected Products

Microsoft 365 Apps (Enterprise, x64 and x86)
Microsoft Office 2016 and Office 2019 (x64 and x86)
Microsoft Office Long Term Servicing Channel 2021 and 2024 (x64, x86, and macOS)

Discovery Timeline

2025-08-12 - CVE-2025-53740 published to the National Vulnerability Database (NVD)
2025-08-12 - Microsoft releases security advisory and patch via Microsoft Security Response Center
2025-08-15 - Last updated in NVD database

Technical Details for CVE-2025-53740

Vulnerability Analysis

The vulnerability is a use-after-free condition in Microsoft Office. Use-after-free flaws occur when an application continues to reference memory after that memory has been released back to the allocator. An attacker who can influence the contents of the freed memory region — typically by triggering a controlled allocation between the free and the subsequent use — can hijack object dispatch, function pointers, or virtual table references. In Microsoft Office, parsing complex document structures has historically been a fertile source of such conditions, where object lifetime is managed across multiple components that handle embedded objects, OLE structures, and document streams.

The attack vector is local, meaning the vulnerable code path is reached on the target machine rather than across the network. Microsoft classifies the attack complexity as low, with no privileges or user interaction required to trigger the flaw in the labeled configuration. Successful exploitation results in arbitrary code execution in the context of the user running Office.

Root Cause

The root cause is improper memory management (CWE-416) in Microsoft Office. A code path frees a heap object but retains a dangling reference that is later dereferenced. When attacker-controlled data reoccupies the freed slot, the dereference operates on attacker-shaped memory, redirecting execution to attacker-chosen logic.

Attack Vector

An attacker delivers or stages a crafted Office document that triggers the vulnerable parsing or object-handling path when the file is opened or processed by an Office application. Because the vector is local, common delivery techniques include phishing attachments, malicious downloads, network shares, and removable media. On exploitation, the attacker gains code execution as the invoking user and can deploy follow-on tooling, persistence, and lateral movement payloads.

No verified proof-of-concept code is available. Microsoft's advisory remains the authoritative technical reference. See the Microsoft CVE-2025-53740 Advisory for vendor details.

Detection Methods for CVE-2025-53740

Indicators of Compromise

Microsoft Office processes such as WINWORD.EXE, EXCEL.EXE, or POWERPNT.EXE spawning unexpected child processes such as cmd.exe, powershell.exe, rundll32.exe, or mshta.exe.
Office applications writing executable content to disk locations such as %TEMP%, %APPDATA%, or %PUBLIC% shortly after opening a document.
Anomalous outbound network connections initiated by Office processes to untrusted hosts immediately after document open.
Crash telemetry or Windows Error Reporting events referencing access violations in Office binaries when handling specific document formats.

Detection Strategies

Hunt for parent-child process relationships where Office binaries spawn scripting interpreters or LOLBins, which is a strong signal of document-borne code execution.
Correlate document open events with file write and network egress events on the same endpoint within a short time window.
Monitor memory protection bypass attempts and exploit mitigation telemetry (CFG, ASLR, DEP) emitted by Office processes.
Apply behavioral detections for in-memory shellcode execution and reflective loading originating from Office address space.

Monitoring Recommendations

Centralize endpoint telemetry, Windows event logs, and Office macro activity in a SIEM or data lake to enable cross-source correlation.
Track patch deployment status across all Office variants listed in the affected products to identify unpatched endpoints.
Alert on document files arriving from external email senders that are opened within minutes by users with elevated privileges or access to sensitive data.

How to Mitigate CVE-2025-53740

Immediate Actions Required

Apply the security update referenced in the Microsoft CVE-2025-53740 Advisory to all affected Office installations.
Inventory endpoints running Microsoft 365 Apps, Office 2016, Office 2019, and Office LTSC 2021/2024 and prioritize patching on hosts handling untrusted documents.
Enable Protected View and Office Application Guard where supported to contain document-borne exploitation.
Restrict execution of macros and Mark-of-the-Web bypass techniques via Group Policy.

Patch Information

Microsoft released a security update addressing CVE-2025-53740 on August 12, 2025. Administrators should consult the Microsoft Security Response Center advisory for the specific KB articles and build numbers corresponding to each affected channel (Current Channel, Monthly Enterprise Channel, Semi-Annual Channel, and LTSC builds). Deploy updates via Microsoft Update, Windows Server Update Services (WSUS), Microsoft Configuration Manager, or Intune according to your environment's patch management process.

Workarounds

Block or quarantine Office document attachments from untrusted senders at the email gateway until patches are deployed.
Enforce attack surface reduction (ASR) rules in Microsoft Defender to block Office applications from creating child processes and injecting into other processes.
Open documents from untrusted sources only within Protected View or a sandboxed environment such as Windows Sandbox.

bash

# Example PowerShell to enable Microsoft Defender ASR rules
# Block Office applications from creating child processes
Set-MpPreference -AttackSurfaceReductionRules_Ids `
    D4F940AB-401B-4EFC-AADC-AD5F3C50688A `
    -AttackSurfaceReductionRules_Actions Enabled

# Block Office applications from injecting code into other processes
Add-MpPreference -AttackSurfaceReductionRules_Ids `
    75668C1F-73B5-4CF0-BB93-3ECF5CB7CC84 `
    -AttackSurfaceReductionRules_Actions Enabled