CVE-2025-27746: Microsoft 365 Apps Use After Free Flaw

CVE-2025-27746 Overview

CVE-2025-27746 is a use-after-free vulnerability [CWE-416] in Microsoft Office that enables local code execution. An unauthorized attacker can execute arbitrary code on a target system after a user opens a malicious Office document. The flaw affects multiple Microsoft Office products including Microsoft 365 Apps, Office 2016, Office 2019, Office LTSC 2021/2024, Office Online Server, and SharePoint Server subscription edition. Microsoft published the advisory on April 8, 2025, and the issue requires user interaction to trigger.

Critical Impact
Successful exploitation grants the attacker code execution in the context of the current user, resulting in high impact to confidentiality, integrity, and availability.

Affected Products

Microsoft 365 Apps (Enterprise)
Microsoft Office 2016 and 2019
Microsoft Office LTSC 2021 and 2024 (Windows and macOS)
Microsoft Office Online Server
Microsoft SharePoint Server Subscription Edition

Discovery Timeline

2025-04-08 - CVE-2025-27746 assigned and published by Microsoft
2025-04-08 - CVE-2025-27746 published to NVD
2025-07-09 - Last updated in NVD database

Technical Details for CVE-2025-27746

Vulnerability Analysis

The vulnerability is a use-after-free condition in Microsoft Office, classified under [CWE-416]. Use-after-free flaws occur when a program continues to reference memory after it has been freed. Attackers can manipulate the freed memory region to control execution flow. In Office, this typically involves crafted document structures that trigger object lifetime mismatches during parsing or rendering.

Exploitation requires the victim to open a malicious file in an affected Office application. Once opened, the crafted document causes Office to release an object while retaining a dangling pointer. The attacker reclaims that memory with controlled data and redirects execution. The result is arbitrary code execution under the privileges of the user running Office.

No public proof-of-concept exploit is available for CVE-2025-27746, and the issue is not listed in the CISA Known Exploited Vulnerabilities catalog. The EPSS score is 0.762%, placing it in the 50th percentile of likelihood of exploitation. Refer to the Microsoft CVE-2025-27746 Advisory for vendor-specific technical detail.

Root Cause

The root cause is improper management of object lifetimes within Office document processing. A reference to an object persists after the object is freed, leaving a dangling pointer that the attacker can groom and reuse to hijack control flow.

Attack Vector

The attack vector is local and requires user interaction. The victim must open an attacker-supplied document such as a Word, Excel, or other Office file. Delivery commonly occurs through phishing email attachments, malicious links, or removable media. No prior authentication on the target system is required.

Detailed exploitation specifics have not been publicly disclosed. Consult the Microsoft Security Response Center advisory for vendor remediation guidance.

Detection Methods for CVE-2025-27746

Indicators of Compromise

Office processes such as WINWORD.EXE, EXCEL.EXE, or POWERPNT.EXE spawning unexpected child processes like cmd.exe, powershell.exe, or rundll32.exe
Office applications loading non-standard DLLs from user-writable directories such as %TEMP% or %APPDATA%
Office documents arriving via email containing embedded objects, OLE streams, or unusual XML parts
Unexpected outbound network connections initiated immediately after a document is opened

Detection Strategies

Monitor parent-child process relationships where Office binaries spawn shell, scripting, or LOLBin processes
Apply behavioral identification for memory corruption patterns such as heap spray activity within Office processes
Inspect inbound email attachments with sandbox detonation to surface document-borne exploits before delivery
Correlate Office crash telemetry (Watson, Windows Error Reporting) with subsequent suspicious process activity

Monitoring Recommendations

Enable Microsoft Defender Attack Surface Reduction rules that block Office from creating child processes and from injecting code into other processes
Collect Sysmon process creation, image load, and network connection events for Office binaries
Track Office version inventory across endpoints to confirm patch deployment status
Forward endpoint telemetry to a centralized analytics platform for retrospective hunts on document-based intrusions

How to Mitigate CVE-2025-27746

Immediate Actions Required

Apply Microsoft's April 2025 security updates to all affected Office installations without delay
Prioritize patching for SharePoint Server and Office Online Server given their server-side exposure
Validate update deployment with Get-WmiObject Win32_QuickFixEngineering or equivalent inventory tooling
Block inbound Office document types from untrusted external senders at the email gateway pending patch rollout

Patch Information

Microsoft released security updates addressing CVE-2025-27746 on April 8, 2025. Administrators should install the relevant Click-to-Run or MSI updates for Microsoft 365 Apps, Office 2016/2019, Office LTSC 2021/2024, Office Online Server, and SharePoint Server. Patch identifiers and download links are listed in the Microsoft CVE-2025-27746 Advisory.

Workarounds

Enable Protected View and Office Application Guard for documents sourced from the internet or email
Configure Office to block macros from files originating from the internet using Group Policy
Restrict the use of legacy binary Office formats and prefer modern OOXML formats with content scanning
Apply the principle of least privilege so users do not operate Office with administrative rights

bash

# Configuration example - Enable ASR rule to block Office child processes
Add-MpPreference -AttackSurfaceReductionRules_Ids D4F940AB-401B-4EFC-AADC-AD5F3C50688A -AttackSurfaceReductionRules_Actions Enabled