CVE-2021-1421
📋 TL;DR
CVE-2021-1421 is a command injection vulnerability in Cisco Enterprise NFV Infrastructure Software (NFVIS) that allows authenticated local attackers to execute arbitrary commands with root privileges. The vulnerability affects users with restricted CLI access who can exploit insufficient input validation in a configuration command. This enables privilege escalation from non-privileged to root-level access on affected devices.
💻 Affected Systems
- Cisco Enterprise NFV Infrastructure Software (NFVIS)
📦 What is this software?
⚠️ Risk & Real-World Impact
Worst Case
An attacker gains complete control of the NFVIS device, can install persistent backdoors, exfiltrate sensitive data, pivot to other network segments, and disrupt NFV services.
Likely Case
Privilege escalation leading to unauthorized configuration changes, service disruption, and potential lateral movement within the network infrastructure.
If Mitigated
Limited impact with proper network segmentation, strict access controls, and monitoring preventing successful exploitation or containing damage.
🎯 Exploit Status
Exploitation requires authenticated access to the restricted CLI; command injection techniques are well-documented and relatively simple to implement.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Release 4.7.1 or later
Vendor Advisory: https://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-nfvis-cmdinj-DkFjqg2j
Restart Required: Yes
Instructions:
1. Download NFVIS Release 4.7.1 or later from Cisco Software Center. 2. Backup current configuration. 3. Upload and install the new release via NFVIS web interface or CLI. 4. Reboot the system as required. 5. Verify the upgrade completed successfully.
🔧 Temporary Workarounds
Restrict CLI Access
allLimit access to the restricted CLI interface to only authorized administrators using strict access controls.
Network Segmentation
allIsolate NFVIS management interfaces from general user networks to reduce attack surface.
🧯 If You Can't Patch
- Implement strict access controls to limit who can authenticate to the NFVIS restricted CLI interface.
- Monitor and audit all CLI commands executed on NFVIS devices for suspicious patterns.
🔍 How to Verify
Check if Vulnerable:
Check NFVIS version via CLI command: 'show version' or web interface System Information page. If version is earlier than 4.7.1, the system is vulnerable.Check Version:
show versionVerify Fix Applied:
After patching, verify version is 4.7.1 or later using 'show version' command. Test restricted CLI commands to ensure proper input validation.📡 Detection & Monitoring
Log Indicators:
- Unusual CLI command execution patterns
- Multiple failed authentication attempts followed by successful login
- Commands with unusual characters or patterns in input fields
Network Indicators:
- Unexpected outbound connections from NFVIS management interface
- Unusual traffic patterns to/from NFVIS device
SIEM Query:
source="nfvis" AND (event_type="cli_command" AND command CONTAINS ["|", ";", "&", "`", "$"])