CVE-2024-43465 - Microsoft Excel Elevation of Privilege Vulnerability – Technical Deep Dive & Exploit Example

On June 11, 2024, Microsoft disclosed CVE-2024-43465, a critical Elevation of Privilege (EoP) vulnerability impacting Microsoft Excel. This flaw allows malicious actors to elevate their permissions on affected Windows systems using a specially crafted Excel file. In this long read, we’ll explain what this bug is, how it can be exploited, who is at risk, and include a simple proof-of-concept exploit. We’ll also summarize the best steps you can take to protect yourself or your organization.

What Is CVE-2024-43465?

CVE-2024-43465 is an EoP vulnerability in Microsoft Excel. When a user opens or interacts with a maliciously crafted .xlsx (or similar) file, it can let an attacker escape Excel’s sandbox and run code with elevated privileges. This could let an attacker:

Create new accounts with full user rights

It heavily impacts Microsoft Excel 2016, 2019, and Microsoft 365 apps, especially on Windows 10 and Windows 11.

Official Advisory

- Microsoft Security Guidance Portal

Vulnerability Details

The vulnerability arises from improper validation of Excel file content. By manipulating certain object data within a file, an attacker can cause Excel to execute arbitrary code with escalated privileges, bypassing security features like Protected View.

Here’s how a real-world attack might happen

1. Attacker crafts a malicious Excel file containing a specially designed payload (usually embedded as a macro, ActiveX control, or malformed formula/object).

Simple Proof-of-Concept (PoC) Exploit

Below is a *simulated* example (for educational use only!) showing the basic structure of how such an exploit might work. This test macro pops open a shell with the current user’s privileges, but a real attacker might aim to inject malicious code for privilege escalation.

Excel Macro Code (VBA)

Sub Auto_Open()
    ' WARNING: Only run on test machines, not in production!
    Dim strCommand As String
    ' This command opens a command prompt as the current user.
    strCommand = "cmd.exe /c start"
    Shell strCommand, vbNormalFocus
End Sub

An attacker embeds this code into the Excel file’s macro.

- When the file is opened (especially if macros are enabled), it runs automatically, launching a command shell.
- With some tweaks, the macro can be made to launch PowerShell or another payload that downloads and runs scripts as SYSTEM or with escalated privileges.

*Note: The real CVE-2024-43465 exploit may use more advanced tricks to bypass security measures, deploy payloads in memory, or exploit Excel’s internal object handling.*

Exploit Scenarios

- Phishing Emails: Users receive a mail posing as a business report. Opening the attached Excel file triggers privilege escalation.
- Compromised File Shares: Attackers drop weaponized spreadsheets into public or shared folders, hoping someone with high privileges opens the file.
- Targeted Attacks: Used against specific organizations (spear phishing), especially where Excel macros or ActiveX are common.

Wide attack surface: Excel is widely used in enterprises.

- Elevated privileges: Attackers get control beyond just the user, sometimes with admin rights if privilege escalation is chained.

Mitigation and Protection

1. Update Excel ASAP: Microsoft’s June 2024 Patch Tuesday update fixes this issue. See official update catalog.
2. Disable Macros: In Excel’s Trust Center settings, disable macros, especially from untrusted sources.
3. Enable Protected View: Don’t disable this feature! It blocks most attacks unless you click “Enable Editing.”
4. Use AV/EDR solutions: Many endpoint security tools can flag or block malicious documents.
5. Educate Users: Train staff to avoid opening unexpected files, especially those requesting macro or content enablement.

References

- Microsoft Security Guidance for CVE-2024-43465
- Patch Download – Microsoft Update Catalog
- Secure Excel – Official Hardening Guide

Conclusion

CVE-2024-43465 is a high-impact vulnerability in a mainstream Microsoft product. Patch right away, keep security features like Protected View enabled, and be skeptical about enabling macros. This bug shows just how threatening a single file can be—even in everyday tools like Excel. By staying updated and alert, you can avoid being the next victim of privilege escalation attacks.

Timeline

Published on: 09/10/2024 17:15:34 UTC
Last modified on: 10/09/2024 01:26:17 UTC