CVE-2021-1580: Cisco APIC RCE Vulnerability Explained

CVE-2021-1580 Overview

Multiple vulnerabilities exist in the web UI and API endpoints of Cisco Application Policy Infrastructure Controller (APIC) and Cisco Cloud APIC that could allow a remote attacker to perform command injection or file upload attacks on affected systems. These vulnerabilities affect critical network infrastructure management components, potentially allowing attackers with elevated privileges to execute arbitrary commands on the underlying operating system.

Critical Impact

Authenticated attackers with high privileges can execute arbitrary commands and upload malicious files, potentially leading to complete system compromise of Cisco APIC infrastructure.

Affected Products

• Cisco Application Policy Infrastructure Controller (APIC)
• Cisco Cloud Application Policy Infrastructure Controller (Cloud APIC)

Discovery Timeline

• 2021-08-25 - CVE-2021-1580 published to NVD
• 2024-11-21 - Last updated in NVD database

Technical Details for CVE-2021-1580

Vulnerability Analysis

This vulnerability combines two dangerous weakness types: CWE-77 (Improper Neutralization of Special Elements used in a Command - Command Injection) and CWE-284 (Improper Access Control). The web UI and API endpoints fail to properly sanitize user-supplied input before passing it to system-level commands, enabling command injection attacks. Additionally, improper access controls in the file upload functionality allow attackers to upload arbitrary files to the affected system.

The attack requires network access and high-level privileges on the target system. Once exploited, an attacker can achieve high impact on confidentiality, integrity, and availability of the affected infrastructure. Given that Cisco APIC serves as the centralized policy and network management controller for Application Centric Infrastructure (ACI) deployments, compromise of this system could have cascading effects across the entire network fabric.

Root Cause

The root cause stems from insufficient input validation in the web UI and API endpoints of Cisco APIC and Cloud APIC. The application fails to properly sanitize special characters and command sequences before incorporating user input into operating system commands. Additionally, access control mechanisms do not adequately restrict file upload capabilities, allowing authenticated users to upload potentially malicious files to sensitive system directories.

Attack Vector

The attack is conducted remotely over the network against the web UI or API endpoints. An attacker must first authenticate to the system with high-level privileges. Once authenticated, the attacker can craft malicious requests that include command injection payloads or upload arbitrary files. The command injection attack allows execution of arbitrary commands with the privileges of the web application service, while the file upload vulnerability could enable deployment of web shells or other malicious payloads.

The vulnerability mechanism involves injecting shell metacharacters or command sequences into API parameters that are processed by backend system commands. When the application constructs shell commands using unsanitized user input, the injected payload executes on the underlying operating system. See the Cisco Security Advisory for detailed technical information.

Detection Methods for CVE-2021-1580

Indicators of Compromise

• Unusual command execution patterns or shell activity originating from APIC web service processes
• Unexpected files appearing in web-accessible directories or system folders on APIC controllers
• Authentication logs showing high-privilege account access followed by anomalous API requests
• System logs containing shell metacharacters (;, |, &&, ||, $()) in web application parameters

Detection Strategies

• Monitor APIC API endpoint access logs for requests containing shell metacharacters or encoded command sequences
• Implement file integrity monitoring on APIC systems to detect unauthorized file uploads or modifications
• Deploy network intrusion detection systems with signatures for command injection patterns targeting Cisco APIC
• Review authentication logs for suspicious high-privilege account activity, especially from unusual source IPs

Monitoring Recommendations

• Enable detailed logging on Cisco APIC web UI and API endpoints to capture all request parameters
• Configure SIEM alerts for command injection attempt patterns in APIC-related log sources
• Establish baseline behavior for administrative API usage and alert on deviations
• Monitor for new or modified files in APIC system directories, particularly executable files or scripts

How to Mitigate CVE-2021-1580

Immediate Actions Required

• Apply the security patches provided by Cisco as outlined in the security advisory
• Restrict network access to APIC management interfaces using firewall rules and access control lists
• Review and audit high-privilege account access, implementing principle of least privilege
• Monitor APIC systems for signs of compromise using the detection strategies outlined above

Patch Information

Cisco has released security updates to address these vulnerabilities. Administrators should consult the Cisco Security Advisory (cisco-sa-capic-mdvul-HBsJBuvW) for specific version information and upgrade instructions. Organizations should prioritize patching APIC systems given the critical role these controllers play in ACI network infrastructure.

Workarounds

• Limit network access to APIC management interfaces to trusted administrative networks only
• Implement additional authentication controls such as multi-factor authentication for high-privilege accounts
• Consider placing APIC management interfaces behind a VPN or jump host to add an additional security layer
• Disable or restrict API access if not operationally required until patches can be applied

# Example: Restrict APIC management access using ACLs
# Apply on network devices protecting APIC management network
access-list APIC-MGMT-RESTRICT permit tcp TRUSTED_ADMIN_NETWORK APIC_MGMT_SUBNET eq 443
access-list APIC-MGMT-RESTRICT deny tcp any APIC_MGMT_SUBNET eq 443 log
access-list APIC-MGMT-RESTRICT deny tcp any APIC_MGMT_SUBNET eq 80 log