CVE-2025-59227: Microsoft 365 Apps Use-After-Free RCE

CVE-2025-59227 Overview

CVE-2025-59227 is a use-after-free vulnerability [CWE-416] in Microsoft Office that allows an unauthorized attacker to execute code locally. The flaw affects Microsoft 365 Apps, Microsoft 365 Copilot, Microsoft Office 2016 and 2019, and Office Long-Term Servicing Channel (LTSC) 2021 and 2024 across x86, x64, macOS, and Android builds. Successful exploitation requires user interaction, typically opening a crafted Office document. Microsoft published the advisory on October 14, 2025.

Critical Impact

An attacker who convinces a user to open a malicious Office file can execute arbitrary code in the context of the current user, leading to compromise of confidentiality, integrity, and availability.

Affected Products

• Microsoft 365 Apps (Enterprise, x86 and x64)
• Microsoft 365 Copilot (Android)
• Microsoft Office 2016 and Microsoft Office 2019 (x86 and x64)
• Microsoft Office LTSC 2021 and Microsoft Office LTSC 2024 (x86, x64, macOS)

Discovery Timeline

• 2025-10-14 - CVE-2025-59227 published to NVD
• 2025-10-14 - Microsoft releases security update through MSRC
• 2026-05-22 - Last updated in NVD database

Technical Details for CVE-2025-59227

Vulnerability Analysis

The vulnerability is a use-after-free condition in Microsoft Office. Use-after-free flaws occur when a program continues to reference memory that has already been released back to the allocator. An attacker who controls the contents of reallocated memory can redirect execution to attacker-supplied data.

In Office, parsing routines for complex document formats frequently allocate, free, and reuse object instances tied to embedded structures, fields, or OLE components. A crafted document can trigger the premature release of one of these objects while a stale pointer remains in scope, then reclaim that memory with attacker-controlled content before the pointer is dereferenced.

Exploitation requires local context with user interaction, consistent with the standard Office attack pattern of delivering a weaponized .docx, .xlsx, .rtf, or related file through email, chat, or web download. No privileges are required prior to exploitation. Code executes with the privileges of the user running Office.

Root Cause

The root cause is improper lifecycle management of a heap-allocated object inside an Office component. A reference to the object remains valid in program state after the object is freed, and a subsequent operation dereferences the stale pointer to call a virtual method or read function pointer data.

Attack Vector

The attack vector is local and requires user interaction. An attacker crafts an Office document containing the malformed structure that triggers the use-after-free, then delivers it through phishing, file sharing, or a drive-by download. When the victim opens the file in a vulnerable Office build, the parser reaches the vulnerable code path and the attacker controls execution flow.

No public proof-of-concept has been published. CVE-2025-59227 is not listed in the CISA Known Exploited Vulnerabilities catalog at the time of publication. The EPSS score is 0.083%.

Technical exploitation specifics have not been disclosed by Microsoft. See the Microsoft Security Update CVE-2025-59227 advisory for vendor guidance.

Detection Methods for CVE-2025-59227

Indicators of Compromise

• Office processes (winword.exe, excel.exe, powerpnt.exe) spawning unexpected child processes such as cmd.exe, powershell.exe, rundll32.exe, or mshta.exe.
• Office applications writing executable content to %TEMP%, %APPDATA%, or user profile directories shortly after a document is opened.
• Crashes in Office processes referencing access violations or heap corruption in Windows Error Reporting telemetry.
• Outbound network connections initiated by Office processes to previously unseen domains or IPs immediately after document open.

Detection Strategies

• Hunt for parent-child process anomalies where Office binaries spawn scripting hosts or living-off-the-land binaries.
• Inspect documents sourced from email and external file shares using sandbox detonation that monitors for memory corruption signatures.
• Correlate Office crash events (Application Error ID 1000) with subsequent process creation or network activity on the same host.
• Behavioral AI engines such as those in Singularity Endpoint identify post-exploitation activity from Office processes, including code execution chains that originate from document parsers.

Monitoring Recommendations

• Forward Sysmon process creation, image load, and file write events from endpoints running Office to a centralized data lake for correlation.
• Track inbound email attachments and SharePoint or OneDrive uploads of Office formats and apply detonation policies before delivery.
• Monitor Office build numbers across the fleet to identify hosts that have not received the October 2025 security update.

How to Mitigate CVE-2025-59227

Immediate Actions Required

• Apply the October 2025 Microsoft Office security updates to all affected Microsoft 365 Apps, Office 2016, Office 2019, and Office LTSC 2021/2024 installations.
• Identify Office build numbers fleet-wide and prioritize systems handling external documents, including mail servers, finance workstations, and executive endpoints.
• Enable Protected View and Office Application Guard for documents originating from the internet and email.
• Reinforce user awareness on not opening unsolicited Office attachments and not clicking through Protected View warnings.

Patch Information

Microsoft released a patch addressing CVE-2025-59227 on October 14, 2025. Refer to the Microsoft Security Update CVE-2025-59227 for build numbers per channel (Current, Monthly Enterprise, Semi-Annual Enterprise) and for the corresponding Click-to-Run and MSI updates. Microsoft 365 Copilot for Android and Office for Mac updates are delivered through their respective app stores.

Workarounds

• Block or quarantine inbound Office attachments at the email gateway until patches are deployed.
• Enforce Attack Surface Reduction (ASR) rules that block Office applications from creating child processes and from injecting code into other processes.
• Disable macros and ActiveX content via Group Policy for users who do not require them.
• Use Microsoft Defender Application Guard or equivalent containerization to isolate Office document processing.

# Example: enable Microsoft Defender ASR rule to block Office child processes (PowerShell)
Set-MpPreference -AttackSurfaceReductionRules_Ids `
  D4F940AB-401B-4EFC-AADC-AD5F3C50688A `
  -AttackSurfaceReductionRules_Actions Enabled