CVE-2021-3061: Palo Alto Prisma Access RCE Vulnerability

CVE-2021-3061 Overview

An OS command injection vulnerability exists in the Palo Alto Networks PAN-OS command line interface (CLI) that enables an authenticated administrator with CLI access to execute arbitrary OS commands, potentially leading to privilege escalation. This vulnerability affects multiple versions of PAN-OS and Prisma Access, representing a significant security risk for organizations using these network security products.

Critical Impact

Authenticated administrators can exploit this command injection vulnerability to escalate privileges and execute arbitrary OS commands on affected Palo Alto Networks devices.

Affected Products

• Palo Alto Networks PAN-OS 8.1 versions earlier than PAN-OS 8.1.20-h1
• Palo Alto Networks PAN-OS 9.0 versions earlier than PAN-OS 9.0.14-h3
• Palo Alto Networks PAN-OS 9.1 versions earlier than PAN-OS 9.1.11-h2
• Palo Alto Networks PAN-OS 10.0 versions earlier than PAN-OS 10.0.8
• Palo Alto Networks PAN-OS 10.1 versions earlier than PAN-OS 10.1.3
• Palo Alto Networks Prisma Access 2.1 (Innovation and Preferred)

Discovery Timeline

• 2021-11-10 - CVE-2021-3061 published to NVD
• 2024-11-21 - Last updated in NVD database

Technical Details for CVE-2021-3061

Vulnerability Analysis

This vulnerability is classified as CWE-78 (Improper Neutralization of Special Elements used in an OS Command), commonly known as OS Command Injection. The flaw resides in the PAN-OS command line interface, which fails to properly sanitize user-supplied input before incorporating it into operating system commands.

When an authenticated administrator interacts with the CLI, certain input fields are passed to system-level commands without adequate validation or sanitization. This allows an attacker with administrative CLI access to inject malicious shell metacharacters or command sequences that are then executed with elevated privileges on the underlying operating system.

The vulnerability requires authentication and administrative privileges to exploit, which limits the attack surface. However, the impact is significant as successful exploitation allows attackers to bypass the intended privilege boundaries of the CLI and gain full control over the device's operating system.

Root Cause

The root cause of this vulnerability lies in improper input validation within the PAN-OS CLI processing logic. The CLI fails to properly neutralize special characters and shell metacharacters in user input before passing that input to operating system command execution functions. This lack of input sanitization allows command injection sequences to be interpreted and executed by the underlying shell.

Attack Vector

The attack vector for CVE-2021-3061 is network-based, requiring an attacker to have authenticated administrative access to the PAN-OS CLI. The exploitation path involves:

1. An attacker first authenticates to the PAN-OS device with valid administrator credentials
2. The attacker accesses the CLI interface either locally or remotely via SSH
3. The attacker crafts malicious input containing OS command injection payloads
4. The malicious commands are executed with elevated privileges on the underlying system
5. The attacker can then perform unauthorized actions, install backdoors, or further compromise the network

The vulnerability manifests when specially crafted input containing shell metacharacters or command separators is processed by the CLI without proper sanitization. For example, common injection techniques involve using characters such as semicolons (;), pipes (|), or command substitution syntax to append malicious commands to legitimate CLI operations. For detailed technical information, refer to the Palo Alto Networks Security Advisory.

Detection Methods for CVE-2021-3061

Indicators of Compromise

• Unusual CLI commands or command patterns in PAN-OS audit logs
• Unexpected processes spawned from CLI sessions on PAN-OS devices
• Anomalous system file modifications or unauthorized configuration changes
• Evidence of shell command execution outside normal CLI operations

Detection Strategies

• Enable and monitor detailed CLI audit logging on all PAN-OS devices
• Implement SIEM rules to detect command injection patterns in administrative session logs
• Use behavioral analysis to identify unusual administrator activity or privilege escalation attempts
• Deploy network monitoring to detect anomalous traffic originating from PAN-OS management interfaces

Monitoring Recommendations

• Review administrative access logs regularly for suspicious CLI activity
• Monitor for unexpected changes to system files or configurations
• Establish baseline administrator behavior and alert on deviations
• Implement alerting for multiple failed authentication attempts followed by successful CLI access

How to Mitigate CVE-2021-3061

Immediate Actions Required

• Upgrade PAN-OS to a patched version immediately (8.1.20-h1, 9.0.14-h3, 9.1.11-h2, 10.0.8, or 10.1.3 or later)
• Restrict CLI access to only essential personnel with legitimate administrative needs
• Review and audit administrator accounts to ensure no unauthorized access exists
• Monitor administrative activity closely until patches can be applied

Patch Information

Palo Alto Networks has released security patches addressing this vulnerability across all affected PAN-OS versions. Organizations should upgrade to the following minimum versions or later:

For Prisma Access 2.1 customers, Palo Alto Networks recommends contacting support for specific remediation guidance. Detailed patch information is available in the Palo Alto Networks Security Advisory.

Workarounds

• Restrict CLI access to trusted administrators only and minimize the number of accounts with CLI privileges
• Implement network segmentation to limit access to management interfaces from trusted networks only
• Enable multi-factor authentication for administrative access where supported
• Consider using Panorama for centralized management to reduce direct CLI access requirements

# Example: Restrict management interface access to specific IP addresses
set deviceconfig system permitted-ip 10.0.0.0/24
set deviceconfig system permitted-ip 192.168.1.0/24
commit