CVE-2025-21364 – This vulnerability allows attackers to bypass s... (How to Fix)

Q: What is the severity of CVE-2025-21364?

CVE-2025-21364 has a CVSS score of 7.8 (HIGH). This vulnerability allows attackers to bypass security features in Microsoft Excel, potentially enabling malicious code execution by opening specially crafted documents. It affects users running vulnerable versions of Microsoft Excel on Windows systems.

📋 TL;DR

This vulnerability allows attackers to bypass security features in Microsoft Excel, potentially enabling malicious code execution by opening specially crafted documents. It affects users running vulnerable versions of Microsoft Excel on Windows systems.

💻 Affected Systems

Products:

Microsoft Excel

Versions: Specific versions as listed in Microsoft Security Update Guide

Operating Systems: Windows

Default Config Vulnerable: ⚠️ Yes

Notes: Requires user to open malicious Excel file; macro security settings may affect exploitability

📦 What is this software?

⚠️ Risk & Real-World Impact

🔴

Worst Case

Remote code execution with user privileges leading to full system compromise, data theft, or ransomware deployment.

🟠

Likely Case

Malicious macro execution leading to credential harvesting, data exfiltration, or lateral movement within networks.

🟢

If Mitigated

Limited impact with proper macro security settings and application control policies in place.

🌐 Internet-Facing: LOW (Excel files typically require user interaction, not directly internet-exposed)

🏢 Internal Only: HIGH (phishing campaigns and malicious documents can bypass security features internally)

🎯 Exploit Status

Public PoC: ✅ No

Weaponized: UNKNOWN

Unauthenticated Exploit: ✅ No

Complexity: MEDIUM

Requires user interaction (opening malicious file); exploit likely involves bypassing macro security features

🛠️ Fix & Mitigation

✅ Official Fix

Patch Version: Latest security updates from Microsoft

Vendor Advisory: https://msrc.microsoft.com/update-guide/vulnerability/CVE-2025-21364

Restart Required: No

Instructions:

1. Open Excel > File > Account > Update Options > Update Now 2. Install latest Windows Updates 3. Verify patch installation in Control Panel > Programs > View installed updates

🔧 Temporary Workarounds

Disable Macros

Windows

Configure Excel to disable all macros without notification

Excel Options > Trust Center > Trust Center Settings > Macro Settings > Disable all macros without notification

Block External Content

Windows

Prevent Excel from loading external content in documents

Excel Options > Trust Center > Trust Center Settings > External Content > Block all external content

🧯 If You Can't Patch

Implement application control to block Excel execution
Use email filtering to block suspicious Excel attachments
Educate users about phishing risks and safe document handling

🔍 How to Verify

Check if Vulnerable:

Check Excel version against patched versions in Microsoft advisory

Check Version:

Excel: File > Account > About Excel (shows version)

Verify Fix Applied:

Verify latest security updates are installed via Windows Update history

📡 Detection & Monitoring

Log Indicators:

Excel crash logs
Suspicious macro execution events
Unusual file opens from email attachments

Network Indicators:

Outbound connections from Excel process to suspicious domains
DNS requests for known malicious domains after Excel file open

SIEM Query:

EventID=1 OR EventID=4688 | where ProcessName contains "EXCEL.EXE" | where CommandLine contains suspicious patterns

📊 Metadata

CVE ID: CVE-2025-21364

CVSS v3 Score: 7.8 (HIGH)

CVSS Vector: CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H

CWE: CWE-502

EPSS Score: 0.58% exploit probability (68.4th percentile)

Published: January 14, 2025

Last Updated: July 1, 2025

🔗 References

https://msrc.microsoft.com/update-guide/vulnerability/CVE-2025-21364 Patch,Vendor Advisory

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