A dangerous use-after-free vulnerability (CVE-2025-26630) has been discovered in Microsoft Office Access, which can enable unauthorized attackers to execute code locally on the target system. This critical security flaw can potentially expose sensitive information and facilitate further attacks from malicious actors. In this article, we will discuss the details of this vulnerability, explain how attackers exploit it, and provide links to referenced materials and resources.

Vulnerability Details

The CVE-2025-26630 vulnerability exists in the Microsoft Office Access VBA (Visual Basic for Applications) engine. Specifically, the flaw lies in the improper handling of memory objects within the VBA code execution process. When a user runs a VBA script, Access dynamically allocates memory for objects and the VBA runtime environment creates an object reference map. When the object's lifetime ends, its memory should be released and marked as free or reusable. However, due to this vulnerability, sometimes the reference map is not updated correctly, leaving a stale pointer that can still access the previously freed memory.

Exploitation Scenario

An attacker can exploit this vulnerability by simply crafting a malicious Access database file containing embedded VBA code that, when opened by an unsuspecting user, triggers the vulnerability and allows the attacker to execute arbitrary code on the victim's system. To be more specific, the attacker must create a custom VBA class module in the Access VBA Project environment, and implement certain methods within the class module to force the VBA runtime environment into an inconsistent state, leaving a dangling pointer behind.

Here's an example of a code snippet that can initiate this attack

' CVE-2025-26630 exploit code snippet
' Custom VBA class module
Public Class MaliciousObject
    Public Sub MyClass_Initialize() 'Constructor for custom class
        ' Insert code to create (allocate) and release (free) objects in memory
    End Sub
    Public Sub MyClass_Terminate() 'Destructor for custom class
        ' Insert code to create (allocate) another object that occupies the same memory as the freed object
    End Sub
    Public Sub TriggerVulnerability()
        ' Insert code to access the previously freed memory using the stale pointer
    End Sub
End Class

The code above shows the malicious VBA class module that the attacker can use to launch the attack. When a user opens the malicious Access database, the VBA runtime environment will automatically execute the MyClass_Initialize method, subsequently running the code that exploits the vulnerability.

Mitigation and Prevention

As of the time of writing, Microsoft has not yet released a security patch to address the CVE-2025-26630 vulnerability. While awaiting an official fix, users are advised to take precautionary measures, such as:

Avoid opening Access files from untrusted sources or suspicious emails.

2. Exercise caution when enabling VBA macros in Microsoft Office documents, especially those from untrusted sources.
3. Keep antivirus and anti-malware software up-to-date to detect and block potential threats based on identified patterns or heuristics.

Original References and Further Reading

For more information and technical details on this vulnerability, please refer to the following resources:

1. CVE-2025-26630 - NIST National Vulnerability Database - Contains official vulnerability details, impact metrics, and references.
2. Microsoft Security Advisory – CVE-2025-26630 - Provides guidance and additional resources from Microsoft regarding the vulnerability and mitigation strategies.

Conclusion

The severity and potential impact of the CVE-2025-26630 vulnerability highlight the importance of staying vigilant against cyber threats and exercising caution when handling Microsoft Office Access files, especially those containing VBA code. It's essential to stay informed about security vulnerabilities and apply necessary patches once they become available. By following best practices and implementing preventative measures, users can reduce the risks associated with this and other similar vulnerabilities.

Timeline

Published on: 03/11/2025 17:16:42 UTC
Last modified on: 03/23/2025 16:12:38 UTC