CVE-2022-41104 - Microsoft Excel Security Feature Bypass Vulnerability Deep Dive

Microsoft Excel is one of the world’s most popular spreadsheet applications, used by private individuals, companies, and institutions alike to manage and analyze data. While known for its versatile features, Excel has also drawn the attention of cyber attackers due to its powerful macro functionality and widespread use. In September 2022, Microsoft disclosed a critical security feature bypass vulnerability in Excel: CVE-2022-41104. In this in-depth post, we break down what this vulnerability is, how it works, and what you should do to protect yourself.

[References and Further Reading](#references)

1. Summary of CVE-2022-41104

CVE-2022-41104 is a security feature bypass vulnerability in Microsoft Excel. In essence, this flaw allows an attacker to manipulate security prompts or bypass certain security mechanisms, making it easier for malicious macros or content to execute without proper user warnings.

- Danger: An attacker can send an Excel file (.xls, .xlsm, etc.) with malicious code that might execute on target's computer with little or no warning.

References

- Microsoft Security Advisory for CVE-2022-41104
- NIST CVE Record

2. How Does the Exploit Work?

Usually, when you open a workbook with macros or active content, Excel displays a security warning (the yellow security bar) asking you to enable or disable macros. CVE-2022-41104's exploit abuses a flaw in how Excel handles such security checks.

Malicious code runs.

VBA Macro Code in ThisWorkbook

Private Sub Workbook_Open()
    Shell "cmd.exe /c calc.exe", vbHide
End Sub

> *SECURITY WARNING: Macros have been disabled.*

But with the CVE-2022-41104 exploit, attackers discovered ways to modify file properties and format (sometimes via OLE objects or MIME encapsulation) so that Excel fails to trigger the warning.

Example file structure change (pseudo-code)

[MS Office document with crafted metadata]
+-- [Workbook]
+-- [Custom Security Properties: Flag=BypassChecks]
+-- [Embedded OLE Macro Stream]

Or, using Python (with oletools), you could create a simple script to check for macros

from oletools.olevba import VBA_Parser

vbaparser = VBA_Parser("evil.xls")
if vbaparser.detect_vba_macros():
    print("Macros found, check for dangerous code!")

But after exploiting CVE-2022-41104, the file may not show as containing macros, *even though the macro exists*—a classic feature bypass.

Impact: Code execution, data theft, ransomware, further malware installation.

- Attack vector: Low, since it requires successful file delivery and user opening the file. But social engineering with trusted-looking documents increases risk.
- Who is at Risk: Anyone running affected Excel versions—especially organizations with weak email screening and endpoint protection.

5. Mitigation Steps

A. Patch Excel

First and foremost, ensure you have installed the official patches issued for your version of Excel

- Microsoft Patch Information

B. Disable Macros by Default

File > Options > Trust Center > Trust Center Settings > Macro Settings

C. Use Protected View  
Though the exploit attempts to bypass this, keeping Protected View enabled helps mitigate unlikely scenarios.

D. User Awareness  
Educate users about the risks of opening unsolicited excel attachments.

E. Email Gateway Protection  
Use email filtering to block or quarantine all unexpected Excel attachments.

6. References and Further Reading

- Microsoft CVE-2022-41104 Official Details & Mitigation
- NIST Vulnerability Database Entry
- Technical Write-ups on Macro Malware (oletools)
- CERT Guidance for Microsoft Office Macro Security

Conclusion

CVE-2022-41104 is a classic example of how criminals constantly find new angles to bypass software security features—not by breaking through a locked door, but by finding a side window left open. By keeping Microsoft Excel updated, using security best practices, and staying informed, individuals and organizations can significantly reduce their risk.

If you’ve got Excel in your workflow (and who doesn’t?), updating and training your team today is well worth it.


*This article was created for educational purposes. Never run untrusted macros on your system.*

Timeline

Published on: 11/09/2022 22:15:00 UTC
Last modified on: 11/10/2022 00:33:00 UTC