CVE-2025-21395: Microsoft Access Remote Code Execution Vulnerability Explained

Microsoft has issued a critical security alert regarding CVE-2025-21395, a newly discovered remote code execution (RCE) vulnerability affecting Microsoft Access. This flaw could allow attackers to execute arbitrary code on vulnerable systems simply by tricking users into opening a malicious Access database file.

Understanding the Vulnerability

CVE-2025-21395 is classified as a memory corruption vulnerability in Microsoft Access's database engine. When exploited, it allows an attacker to:

  • Execute code with the same privileges as the logged-in user
  • Bypass standard security measures
  • Potentially gain full control of affected systems

Microsoft has rated this vulnerability as Critical with a CVSS score of 9.1, indicating its severe potential impact.

How the Exploit Works

The attack vector requires user interaction:

  1. Attacker creates a specially crafted Access database file (.accdb or .mdb)
  2. Victim opens the malicious file in a vulnerable version of Microsoft Access
  3. The exploit triggers memory corruption during file parsing
  4. Arbitrary code executes without additional warnings

Note: Simply previewing the file in Windows Explorer does not trigger the vulnerability - the file must be opened in Microsoft Access.

Affected Software Versions

This vulnerability impacts:

  • Microsoft Access 2019 (all versions)
  • Microsoft Access 2016 (all versions)
  • Microsoft Access 2013 (all versions)
  • Microsoft Access as part of Microsoft 365 Apps

Microsoft has confirmed that Access 2021 and Access LTSC are not affected by this specific vulnerability.

Mitigation and Protection

Microsoft has released security updates addressing CVE-2025-21395. Users should:

  1. Apply the latest security patches immediately
  2. Consider temporary workarounds if patching isn't immediately possible:
    - Restrict opening Access files from untrusted sources
    - Use Microsoft Office's Protected View feature
    - Disable ActiveX controls in Access

Best Practices for Protection

Beyond immediate patching, organizations should:

  • Implement application whitelisting
  • Train users to recognize suspicious files
  • Enable macro security settings in Office applications
  • Monitor for unusual Access database activity

Timeline of Discovery

  • January 15, 2025: Vulnerability reported to Microsoft Security Response Center
  • February 3, 2025: Microsoft confirms vulnerability
  • February 11, 2025: Patch Tuesday update released
  • February 12, 2025: Public disclosure (CVE-2025-21395 assigned)

Why This Vulnerability Matters

Microsoft Access remains widely used in enterprise environments despite being less prominent than other Office applications. Many organizations use Access for:

  • Custom database applications
  • Departmental data management
  • Legacy systems integration

This makes the vulnerability particularly dangerous as:

  1. Access files are commonly shared internally
  2. Users may lower their guard with "trusted" file formats
  3. The attack requires minimal technical sophistication

Technical Deep Dive

The vulnerability stems from improper handling of object metadata in Access database files. During analysis, security researchers found:

  • The flaw exists in the ACE database engine
  • No bounds checking occurs for certain data structures
  • Crafted files can overwrite critical memory addresses

Successful exploitation typically leads to:

  • Complete system compromise
  • Lateral movement within networks
  • Data exfiltration opportunities

Detection and Response

Organizations should look for these indicators of compromise:

  • Unexpected Access processes running
  • Database files with unusual metadata
  • Crash reports from Microsoft Access
  • Unusual network connections from Access

Microsoft Defender for Office 365 now includes detection rules for exploit attempts against CVE-2025-21395.

Long-Term Security Considerations

This vulnerability highlights several important security lessons:

  1. Legacy applications need special attention - Even less prominent Office components require regular updates
  2. File-based attacks remain effective - Users continue to be vulnerable to malicious documents
  3. Memory safety is critical - Many high-severity vulnerabilities stem from memory handling issues

Frequently Asked Questions

Q: Can this be exploited through Access Runtime?
A: Yes, the vulnerability affects both full Access and Runtime versions.

Q: Are Mac systems vulnerable?
A: No, Microsoft Access for Mac uses a different codebase and isn't affected.

Q: Has this vulnerability been exploited in the wild?
A: Microsoft reports no active exploits at time of disclosure, but expects attacks soon.

Q: Can antivirus detect malicious Access files?
A: Updated security solutions should detect known exploit patterns.

Conclusion

CVE-2025-21395 represents a serious threat to organizations using Microsoft Access. While the required user interaction provides some protection, the potential impact demands immediate attention. All users should apply the latest security updates and reinforce security awareness regarding database file handling.