CVE-2021-35064: Kramerav Viaware Privilege Escalation

CVE-2021-35064 Overview

CVE-2021-35064 is a privilege escalation vulnerability affecting KramerAV VIAWare, a wireless presentation and collaboration solution. The vulnerability exists due to misconfiguration of the sudo utility, which permits unprivileged users to execute multiple dangerous commands including unzip, systemctl, and dpkg. This improper access control flaw allows attackers to escalate privileges and potentially gain full control of affected systems.

Critical Impact

This vulnerability allows unauthenticated remote attackers to escalate privileges and execute arbitrary commands with elevated permissions, potentially leading to complete system compromise.

Affected Products

• KramerAV VIAWare (all tested versions)

Discovery Timeline

• 2021-07-12 - CVE-2021-35064 published to NVD
• 2024-11-21 - Last updated in NVD database

Technical Details for CVE-2021-35064

Vulnerability Analysis

This privilege escalation vulnerability stems from improper access control (CWE-269) in the sudo configuration of KramerAV VIAWare systems. The sudoers file is configured to allow execution of several powerful system commands without proper authentication or privilege verification. The flaw enables network-based attacks without requiring prior authentication or user interaction, making it particularly dangerous for internet-exposed systems.

The affected commands—unzip, systemctl, and dpkg—are particularly dangerous in this context. Each of these utilities can be leveraged to execute arbitrary code or manipulate system services. An attacker can exploit this misconfiguration to install malicious packages, start unauthorized services, or extract malicious archives that overwrite critical system files.

Root Cause

The root cause of this vulnerability is an insecure default configuration in the sudoers file. The VIAWare system permits users to run dangerous system administration commands via sudo without proper authentication controls. This represents a fundamental violation of the principle of least privilege, where users are granted excessive permissions that extend far beyond what is necessary for normal operation.

Attack Vector

The attack vector is network-based, allowing remote exploitation. An attacker can connect to an exposed VIAWare system and leverage the misconfigured sudo permissions to execute privileged commands. The exploitation chain typically involves:

1. Gaining initial access to the VIAWare system (potentially through other exposed services)
2. Identifying the overly permissive sudo configuration
3. Using permitted commands like dpkg to install malicious packages or systemctl to enable backdoor services
4. Achieving full root-level access to the underlying system

The vulnerability mechanism centers on the sudo misconfiguration. When a user executes a command with sudo, the system checks the sudoers file to determine if the action is permitted. In vulnerable VIAWare installations, commands such as sudo dpkg -i malicious.deb or sudo systemctl enable backdoor.service are allowed without password verification, enabling attackers to install arbitrary software or manipulate system services. For additional technical details, see the Packet Storm RCE Advisory.

Detection Methods for CVE-2021-35064

Indicators of Compromise

• Unusual sudo command executions involving unzip, systemctl, or dpkg from non-administrative users
• New system services or daemons appearing without authorized changes
• Unexpected package installations visible in dpkg logs (/var/log/dpkg.log)
• Modifications to the sudoers file or /etc/sudoers.d/ directory

Detection Strategies

• Monitor authentication logs and sudo command history for unusual patterns of privileged command execution
• Implement file integrity monitoring (FIM) on critical system directories and configuration files
• Deploy network intrusion detection rules to identify exploitation attempts targeting VIAWare systems
• Review audit logs for suspicious systemctl operations, particularly service enablement or daemon starts

Monitoring Recommendations

• Enable comprehensive logging for all sudo command executions on VIAWare devices
• Configure SIEM alerts for patterns matching privilege escalation attempts, including unexpected dpkg or systemctl usage
• Implement network segmentation to isolate presentation systems from critical infrastructure
• Establish baseline behavior for VIAWare systems to detect anomalous activity

How to Mitigate CVE-2021-35064

Immediate Actions Required

• Isolate affected VIAWare devices from network segments containing sensitive resources
• Restrict network access to VIAWare systems using firewall rules, limiting exposure to trusted networks only
• Audit the sudoers configuration and remove unnecessary command permissions
• Contact KramerAV support to obtain information about available patches or firmware updates

Patch Information

Organizations should consult the Kramer AV Product Information page for the latest firmware updates and security patches. Apply vendor-provided updates as soon as they become available. Due to the severity of this vulnerability, prioritize patching or implementing compensating controls immediately.

Workarounds

• Manually edit the sudoers configuration to remove or restrict access to dangerous commands (unzip, systemctl, dpkg)
• Implement network access controls to limit who can reach VIAWare devices remotely
• Place VIAWare systems on isolated VLANs without direct internet access
• Enable additional authentication mechanisms where possible to protect administrative functions

# Example: Restricting sudo permissions (review your specific configuration)
# Edit sudoers file safely using visudo
sudo visudo

# Remove or comment out lines that permit unrestricted access to dangerous commands
# Example problematic line to remove or restrict:
# user ALL=(ALL) NOPASSWD: /usr/bin/dpkg, /bin/systemctl, /usr/bin/unzip