CVE-2021-41286
📋 TL;DR
CVE-2021-41286 is an authentication bypass vulnerability in Omikron MultiCash Desktop where password validation occurs client-side. Attackers can manipulate the login function to gain unauthorized access to any account, including administrative accounts. This affects all users of vulnerable MultiCash Desktop installations.
💻 Affected Systems
- Omikron MultiCash Desktop
📦 What is this software?
Multicash by Omikron
⚠️ Risk & Real-World Impact
Worst Case
Complete compromise of the MultiCash system allowing attackers to access all financial data, modify transactions, and perform unauthorized financial operations as any user including administrators.
Likely Case
Unauthorized access to sensitive financial data and potential manipulation of accounting records by attackers with local access to the system.
If Mitigated
Limited impact if proper network segmentation, application whitelisting, and administrative access controls are implemented.
🎯 Exploit Status
Exploitation requires local access to the system and basic reverse engineering skills. Attackers can use debuggers or binary patching to manipulate the login function return value.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Contact Omikron for patched version
Vendor Advisory: https://www.syss.de/fileadmin/dokumente/Publikationen/Advisories/SYSS-2021-047.txt
Restart Required: Yes
Instructions:
1. Contact Omikron support for the patched version
2. Backup current configuration and data
3. Install the updated version
4. Restart the application and verify authentication works correctly
🔧 Temporary Workarounds
Application Whitelisting
windowsRestrict execution of MultiCash Desktop to prevent unauthorized modifications or debugging
Using Windows AppLocker or similar: New-AppLockerPolicy -RuleType Publisher,Path -User Everyone -Action Deny
Network Segmentation
windowsIsolate MultiCash systems from general network access
Windows Firewall: New-NetFirewallRule -DisplayName "Block MultiCash Network" -Direction Inbound -Program "C:\Path\To\MultiCash.exe" -Action Block
🧯 If You Can't Patch
- Implement strict access controls to limit who can physically or remotely access systems running MultiCash Desktop
- Deploy endpoint detection and response (EDR) solutions to monitor for debugging tools and unauthorized process manipulation
🔍 How to Verify
Check if Vulnerable:
Check if MultiCash Desktop version is 4.00.008.SP5 or earlier. Verify if authentication validation occurs client-side by examining the login process behavior.Check Version:
Check application properties or About dialog in MultiCash Desktop interfaceVerify Fix Applied:
Test authentication with incorrect credentials after patch installation. The application should properly reject invalid login attempts.📡 Detection & Monitoring
Log Indicators:
- Multiple failed login attempts followed by successful login from same system
- Unusual account access patterns or administrative access from non-standard workstations
Network Indicators:
- Database connections from unexpected user accounts or systems
- Unusual transaction patterns in financial data
SIEM Query:
source="multicash.log" AND (event_type="login" AND result="success" AND previous_attempts>3) OR (user="admin" AND source_ip NOT IN allowed_admin_ips)