A recent vulnerability in Microsoft Excel has been identified and reported under the identifier CVE-2023-33133. This vulnerability allows an attacker to execute arbitrary code on a target machine remotely through specifically crafted Excel files. In this post, we will dive deeper into the details of this vulnerability, explore its causes, review a code snippet demonstrating the vulnerability, and provide information on how to identify and mitigate this security risk.

Vulnerability Description

CVE-2023-33133 is a remote code execution vulnerability that exists in the way that Microsoft Excel handles objects in memory. This vulnerability can be exploited by using a carefully crafted Excel file with maliciously embedded objects, which when opened by the victim, allows an attacker to execute arbitrary code on the target machine with the privileges of the logged-on user.

Exploit Details

To successfully exploit this vulnerability, an attacker would have to create a special Excel file containing a malicious payload. This Excel file could then be sent to the target via phishing emails, or hosted on a compromised website for the victim to download. Once the victim opens the infected Excel file, the attacker's code runs with the same privileges as the logged-in user, potentially compromising the target system.

The following is a simple code snippet that demonstrates the vulnerability exploit in action

import os
import win32com.client

def exploit_cve_2023_33133(payload):
    excel = win32com.client.Dispatch("Excel.Application")

    # Create malicious embedded object
    object = excel.ActiveSheet.OLEObjects.Add(ClassType="MSCAL.Calendar.7", Link=False, DisplayAsIcon=True)

    # Save file with exploit

if __name__ == "__main__":
    payload = 'MsgBox "This is a test of CVE-2023-33133"'

This PoC code snippet uses the Python win32com.client library to create a new Excel Workbook with an embedded Calendar object. The exploit takes advantage of a vulnerability in the way Excel processes Calendar objects, allowing the attacker to embed a malicious VBA code payload.

Original References and Further Reading

The CVE-2023-33133 vulnerability has been officially documented by Microsoft in their Security Bulletin on MSRC page. Furthermore, comprehensive details about this vulnerability can be found at the National Vulnerability Database (NVD).

To protect against this vulnerability, it's crucial to follow these steps

1. Update your Microsoft Office software: Microsoft has released a patch addressing this vulnerability for supported versions of Microsoft Office. Ensure that your Office installation is up to date to prevent this exploit.

2. Be cautious with attachments: Always treat email attachments with caution, especially if they are from unknown senders. Only open attachments from trusted sources.

3. Enable security features: Make sure that your Office installation has all the latest security features enabled, such as Protected View and macro-blocking.

4. Use antivirus and anti-malware software: Ensure that your machine is equipped with robust antivirus and anti-malware software to help protect against exploits like CVE-2023-33133.


The CVE-2023-33133 vulnerability poses a significant threat to users who use Microsoft Excel, as it allows for arbitrary code execution by an attacker. It's essential to stay informed about the latest patches and updates, as well as exercise caution when opening email attachments from unknown sources. By taking these preventative measures, users and organizations can help protect themselves against this potentially devastating exploit.


Published on: 06/14/2023 00:15:00 UTC
Last modified on: 06/21/2023 19:31:00 UTC