CVE-2021-21535
📋 TL;DR
CVE-2021-21535 is a missing authentication vulnerability in Dell Hybrid Client that allows local unauthenticated attackers to gain root access. This affects Dell Hybrid Client versions before 1.5, potentially compromising the entire system. Attackers with physical or remote access to the device can exploit this to take full control.
💻 Affected Systems
- Dell Hybrid Client
📦 What is this software?
⚠️ Risk & Real-World Impact
Worst Case
Complete system compromise with root-level persistence, data theft, lateral movement to other systems, and installation of backdoors or ransomware.
Likely Case
Local attacker gains administrative control, accesses sensitive data, modifies system configurations, and potentially uses the system as a foothold for further attacks.
If Mitigated
Limited impact with proper network segmentation, minimal local user access, and monitoring in place, though root access still poses significant risk.
🎯 Exploit Status
The vulnerability requires local access but no authentication, making exploitation straightforward for attackers with any level of access to the system.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Dell Hybrid Client 1.5 and later
Vendor Advisory: https://www.dell.com/support/kbdoc/en-us/000184667/dsa-2021-071-dell-hybrid-client-security-update-for-multiple-vulnerabilities
Restart Required: Yes
Instructions:
1. Download Dell Hybrid Client version 1.5 or later from Dell's support site. 2. Backup system data. 3. Install the update following Dell's documentation. 4. Reboot the system. 5. Verify the update was successful.
🔧 Temporary Workarounds
Restrict Local Access
allLimit physical and remote access to Dell Hybrid Client systems to authorized personnel only.
Network Segmentation
allIsolate Dell Hybrid Client systems from critical network segments to limit lateral movement.
🧯 If You Can't Patch
- Implement strict access controls to limit who can physically or remotely access the system
- Monitor system logs for unauthorized access attempts and privilege escalation activities
🔍 How to Verify
Check if Vulnerable:
Check the Dell Hybrid Client version via system settings or command line. If version is below 1.5, the system is vulnerable.Check Version:
Check system information in Dell Hybrid Client interface or consult Dell documentation for version checking commands.Verify Fix Applied:
After updating, verify the version is 1.5 or higher and test that authentication is required for critical functions.📡 Detection & Monitoring
Log Indicators:
- Unauthenticated access attempts to critical functions
- Unexpected privilege escalation events
- Authentication bypass logs
Network Indicators:
- Unusual outbound connections from Dell Hybrid Client systems
- Traffic patterns indicating lateral movement
SIEM Query:
Search for authentication failures followed by successful privileged access on Dell Hybrid Client systems