CVE-2021-42855
📋 TL;DR
CVE-2021-42855 is a local privilege escalation vulnerability in SteelCentral AppInternals Dynamic Sampling Agent (DSA) where an attacker with local access can write malicious commands to a misconfigured debug configuration file. When the agent processes this file via its API, it executes those commands with elevated privileges. This affects organizations using vulnerable versions of Riverbed SteelCentral AppInternals.
💻 Affected Systems
- Riverbed SteelCentral AppInternals Dynamic Sampling Agent (DSA)
📦 What is this software?
Steelcentral Appinternals Dynamic Sampling Agent by Riverbed
View all CVEs affecting Steelcentral Appinternals Dynamic Sampling Agent →
⚠️ Risk & Real-World Impact
Worst Case
Full system compromise via arbitrary command execution with SYSTEM/root privileges, enabling lateral movement, data exfiltration, or ransomware deployment.
Likely Case
Local attackers gain administrative privileges on affected systems, allowing them to install malware, steal credentials, or disable security controls.
If Mitigated
Minimal impact with proper file permissions and network segmentation limiting attacker access to vulnerable systems.
🎯 Exploit Status
Exploitation requires local access to write to the configuration file, but the technique is straightforward once access is obtained.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: 12.14.0 and later
Restart Required: Yes
Instructions:
1. Download and install SteelCentral AppInternals DSA version 12.14.0 or later from Riverbed support portal. 2. Restart the DSA service. 3. Verify the .debug_command.config file now has restricted permissions.
🔧 Temporary Workarounds
Restrict File Permissions
allManually set proper permissions on the .debug_command.config file to prevent unauthorized writes.
Windows: icacls "C:\Program Files\Riverbed\AppInternals\Agent\.debug_command.config" /inheritance:r /grant "SYSTEM:(R)" /grant "Administrators:(R)"
Linux: chmod 600 /opt/riverbed/appinternals/agent/.debug_command.config && chown root:root /opt/riverbed/appinternals/agent/.debug_command.config
🧯 If You Can't Patch
- Remove write permissions for non-administrative users from the .debug_command.config file using the workaround commands.
- Implement strict access controls and monitoring on systems running vulnerable DSA agents to detect unauthorized local access attempts.
🔍 How to Verify
Check if Vulnerable:
Check if DSA version is below 12.14.0 and verify the .debug_command.config file has insecure write permissions (e.g., non-admin users can modify it).Check Version:
Windows: Check agent logs or installed programs list. Linux: Check /opt/riverbed/appinternals/agent/version.txt or agent status output.Verify Fix Applied:
Confirm DSA version is 12.14.0 or higher and that .debug_command.config file permissions only allow SYSTEM/root and administrators to write.📡 Detection & Monitoring
Log Indicators:
- Unauthorized modifications to .debug_command.config file in file integrity monitoring logs
- Unusual command execution events from the DSA agent process in system logs
Network Indicators:
- Unusual outbound connections from DSA agent systems following local privilege escalation
SIEM Query:
Example: (event_source="file_integrity" AND file_path="*debug_command.config") OR (process_name="AppInternalsAgent" AND command_line_contains="suspicious_command")🔗 References
- https://aternity.force.com/customersuccess/s/article/Local-privilege-escalation-due-to-misconfigured-write-permission-on-debug-command-config-file-CVE-2021-42855
- https://aternity.force.com/customersuccess/s/article/Local-privilege-escalation-due-to-misconfigured-write-permission-on-debug-command-config-file-CVE-2021-42855
