CVE-2025-62553: Microsoft 365 Apps Use After Free Flaw

CVE-2025-62553 Overview

CVE-2025-62553 is a use-after-free vulnerability [CWE-416] in Microsoft Office Excel that allows an unauthorized attacker to execute code locally on a targeted system. The flaw affects Microsoft 365 Apps, Excel 2016, Office 2019, and Office Long Term Servicing Channel 2021 and 2024 across both x86 and x64 builds, including macOS distributions of the LTSC editions. Exploitation requires a user to open a crafted Excel document, after which the attacker can run arbitrary code in the context of the current user. Microsoft published the advisory and corresponding security update through the Microsoft Security Response Center.

Critical Impact
Successful exploitation grants arbitrary code execution with the privileges of the user opening the malicious Excel file, enabling malware deployment, credential theft, and lateral movement.

Affected Products

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

Discovery Timeline

2025-12-09 - CVE-2025-62553 published to NVD
2025-12-09 - Last updated in NVD database

Technical Details for CVE-2025-62553

Vulnerability Analysis

The vulnerability is a use-after-free condition within Microsoft Office Excel. Use-after-free flaws occur when a program continues to reference memory after that memory has been released back to the allocator. An attacker who controls the contents and timing of subsequent allocations can place attacker-influenced data into the freed region. When the dangling pointer is dereferenced, the application operates on attacker-controlled structures, which can be steered toward arbitrary code execution.

In this case, Excel parses a crafted spreadsheet that triggers premature object deallocation while a pointer to that object remains in active use. The attack vector is local and requires user interaction, consistent with the typical Office exploitation pattern of phishing a victim to open a weaponized .xlsx, .xls, or .xlsm document. Once executed, attacker code runs in the user's security context and can chain with privilege escalation flaws for broader compromise.

Root Cause

The root cause is improper object lifetime management in an Excel document-parsing component. A specific document structure causes Excel to free an internal object while still holding a reference to it, producing a dangling pointer that the application later dereferences during continued processing.

Attack Vector

An attacker delivers a malicious Excel workbook via email, web download, or shared storage. When the victim opens the file, Excel processes the crafted content and triggers the dangling pointer dereference. Through heap grooming, the attacker places shellcode or a controlled object at the reused address, leading to local code execution with the rights of the logged-on user.

No verified proof-of-concept is publicly available. For technical details, refer to the Microsoft Security Update for CVE-2025-62553.

Detection Methods for CVE-2025-62553

Indicators of Compromise

Unexpected child processes spawned by excel.exe, such as cmd.exe, powershell.exe, wscript.exe, mshta.exe, or rundll32.exe.
Excel writing executable content, scripts, or DLLs to user-writable paths including %TEMP%, %APPDATA%, and %LOCALAPPDATA%.
Crash or exception events in excel.exe involving heap corruption shortly after a document is opened.
Outbound network connections from excel.exe to uncategorized or newly registered domains following document open events.

Detection Strategies

Monitor for process lineage anomalies where Office binaries spawn scripting or LOLBins, mapping to MITRE ATT&CK techniques T1566.001 and T1204.002.
Hunt for Excel processes loading unsigned modules or modules from user-writable directories.
Inspect inbound mail attachments and SharePoint uploads for Excel files containing unusual embedded objects, OLE streams, or malformed BIFF/OOXML structures.

Monitoring Recommendations

Enable and forward Microsoft 365 audit logs and Defender for Office 365 attachment telemetry to a centralized SIEM for correlation.
Track Office version compliance across endpoints and alert when unpatched Excel builds open attachments from external senders.
Capture endpoint EDR telemetry for memory access violations within excel.exe and correlate with recent document-open events.

How to Mitigate CVE-2025-62553

Immediate Actions Required

Apply the Microsoft security update referenced in the MSRC advisory for CVE-2025-62553 to all affected Office and Microsoft 365 Apps installations.
Enforce Protected View and Office Trust Center policies that block macros, ActiveX, and external content for files originating from the internet.
Restrict execution of child processes spawned by Office applications using Microsoft Defender Attack Surface Reduction (ASR) rules.
Educate users on phishing patterns that deliver Excel attachments and require sandboxed previewing for untrusted documents.

Patch Information

Microsoft has issued a security update addressing CVE-2025-62553. Administrators should deploy the December 2025 patch package through Microsoft Update, Microsoft 365 Apps update channels, or WSUS/Intune. macOS users of Office LTSC 2021 and 2024 must update through Microsoft AutoUpdate. Confirm patch installation by validating Excel build numbers against those listed in the MSRC advisory.

Workarounds

Block inbound Excel attachments from untrusted senders at the email gateway until patches are deployed.
Configure Group Policy to open all Excel files from the internet and untrusted locations in Protected View without the option to enable editing.
Enable the ASR rule Block all Office applications from creating child processes to limit post-exploitation behaviors.

bash

# Enable ASR rule to block Office apps from creating child processes (PowerShell)
Add-MpPreference -AttackSurfaceReductionRules_Ids D4F940AB-401B-4EFC-AADC-AD5F3C50688A `
                 -AttackSurfaceReductionRules_Actions Enabled