CVE-2023-23399
📋 TL;DR
CVE-2023-23399 is a remote code execution vulnerability in Microsoft Excel that allows attackers to execute arbitrary code by tricking users into opening specially crafted Excel files. This affects users of vulnerable Microsoft Excel versions who open malicious documents. The vulnerability stems from improper bounds checking when processing Excel files.
💻 Affected Systems
- Microsoft Excel
📦 What is this software?
365 Apps by Microsoft
Excel by Microsoft
Excel by Microsoft
Excel by Microsoft
Office by Microsoft
Office by Microsoft
Office by Microsoft
Office by Microsoft
Office by Microsoft
Office Long Term Servicing Channel by Microsoft
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⚠️ Risk & Real-World Impact
Worst Case
Complete system compromise with attacker gaining full control of the victim's computer, data theft, ransomware deployment, and lateral movement within the network.
Likely Case
Malware installation, credential theft, and data exfiltration through malicious Excel documents delivered via phishing or malicious websites.
If Mitigated
Limited impact with proper email filtering, user awareness training, and application sandboxing preventing successful exploitation.
🎯 Exploit Status
Exploitation requires user interaction to open malicious file. No public exploit code available but likely being used in targeted attacks.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Security updates released in March 2023 patch cycle
Vendor Advisory: https://msrc.microsoft.com/update-guide/vulnerability/CVE-2023-23399
Restart Required: Yes
Instructions:
1. Open Microsoft Excel. 2. Go to File > Account > Update Options > Update Now. 3. Restart Excel after update completes. For enterprise deployments, deploy through Microsoft Update or WSUS.
🔧 Temporary Workarounds
Block Excel file types via email filtering
allConfigure email gateways to block or quarantine Excel files (.xls, .xlsx, .xlsm) from untrusted sources
Enable Protected View
windowsEnsure Protected View is enabled for files from the internet to prevent automatic macro execution
File > Options > Trust Center > Trust Center Settings > Protected View > Enable all options
🧯 If You Can't Patch
- Implement application whitelisting to prevent unauthorized Excel execution
- Deploy Microsoft Office in Application Guard or similar sandboxing environment
🔍 How to Verify
Check if Vulnerable:
Check Excel version and compare with patched versions in Microsoft advisory. Vulnerable if before March 2023 security updates.Check Version:
In Excel: File > Account > About Excel shows version numberVerify Fix Applied:
Verify Excel version is updated to March 2023 or later security update. Check Windows Update history for KB5002255 or similar.📡 Detection & Monitoring
Log Indicators:
- Excel crash logs with memory access violations
- Windows Event Logs showing Excel spawning unusual child processes
Network Indicators:
- Excel making unexpected outbound connections after opening files
- DNS requests to suspicious domains following Excel file opens
SIEM Query:
source="*excel*" AND (event_id=1000 OR process_name="cmd.exe" OR process_name="powershell.exe")