CVE-2020-3205: Cisco IOS RCE Vulnerability via Inter-VM

CVE-2020-3205 Overview

A command injection vulnerability exists in the implementation of the inter-VM channel of Cisco IOS Software for Cisco 809 and 829 Industrial Integrated Services Routers (Industrial ISRs) and Cisco 1000 Series Connected Grid Routers (CGR1000). This vulnerability allows an unauthenticated, adjacent attacker to execute arbitrary shell commands on the Virtual Device Server (VDS) of an affected device.

The vulnerability stems from insufficient validation of signaling packets destined to VDS. An attacker can exploit this vulnerability by sending malicious packets to an affected device, potentially achieving arbitrary command execution in the context of the Linux shell of VDS with root privileges. Due to the hypervisor architecture design of these devices, successful exploitation may lead to complete system compromise.

Critical Impact

Unauthenticated adjacent attackers can execute arbitrary shell commands with root privileges on the Virtual Device Server, potentially leading to complete system compromise of industrial routers and connected grid infrastructure.

Affected Products

• Cisco IOS Software (versions 12.2 through 15.9)
• Cisco 809 Industrial Integrated Services Router
• Cisco 829 Industrial Integrated Services Router
• Cisco 1120 Connected Grid Router
• Cisco 1240 Connected Grid Router

Discovery Timeline

• June 3, 2020 - CVE-2020-3205 published to NVD
• November 21, 2024 - Last updated in NVD database

Technical Details for CVE-2020-3205

Vulnerability Analysis

This vulnerability affects the inter-VM communication channel within Cisco's industrial router platforms that utilize a hypervisor-based architecture. The affected devices run multiple virtual machines, including the main IOS instance and a Virtual Device Server (VDS) running Linux. The inter-VM channel facilitates communication between these components but fails to properly validate incoming signaling packets.

The vulnerability is classified under CWE-20 (Improper Input Validation) and CWE-78 (OS Command Injection), indicating that the root cause involves accepting malformed or malicious input that is then passed to shell command execution without proper sanitization. The attack requires adjacent network access, meaning the attacker must be on the same network segment as the target device.

Root Cause

The root cause of this vulnerability is insufficient validation of signaling packets that are destined to the Virtual Device Server (VDS). When packets are received through the inter-VM channel, the IOS software fails to properly sanitize the input before processing. This allows specially crafted packets to inject arbitrary shell commands that execute within the VDS Linux environment with elevated privileges.

Attack Vector

The attack requires the adversary to have adjacent network access to the target device. From this position, the attacker can craft and send malicious UDP packets targeting the inter-VM channel communication pathway. The lack of proper input validation allows these malicious packets to be processed by the VDS, resulting in command injection.

The attack flow involves:

1. Attacker gains adjacent network access to the target Cisco industrial router
2. Malicious signaling packets are crafted to contain shell command payloads
3. Packets are sent to the affected device's inter-VM channel interface
4. The VDS processes these packets without proper validation
5. Injected commands execute in the Linux shell context with root privileges
6. Due to the hypervisor architecture, this may enable complete system compromise

Detection Methods for CVE-2020-3205

Indicators of Compromise

• Unexpected or unauthorized shell commands executing on the VDS component
• Anomalous network traffic patterns targeting inter-VM communication channels
• Unusual process activity or new processes spawning on the Virtual Device Server
• Log entries indicating command execution from the VDS with suspicious parameters

Detection Strategies

• Monitor network traffic for malformed or suspicious UDP packets directed at industrial router interfaces
• Implement network intrusion detection signatures for packets targeting inter-VM communication channels
• Review system logs on affected Cisco devices for signs of unauthorized command execution
• Deploy network segmentation monitoring to detect adjacent network attack attempts

Monitoring Recommendations

• Enable detailed logging on affected Cisco IOS devices to capture inter-VM channel activity
• Implement network traffic analysis to identify anomalous packets targeting affected router models
• Configure alerting for any unexpected administrative access or configuration changes on industrial routers
• Establish baseline behavior for VDS processes to detect deviations indicating compromise

How to Mitigate CVE-2020-3205

Immediate Actions Required

• Apply the security patch provided by Cisco immediately for all affected devices
• Implement strict network segmentation to limit adjacent network access to industrial routers
• Review and restrict physical and network access to segments containing affected devices
• Monitor affected devices for any signs of exploitation or compromise

Patch Information

Cisco has released software updates that address this vulnerability. Administrators should consult the Cisco Security Advisory for specific fixed software versions and upgrade guidance. The advisory provides detailed information on determining if your device is running a vulnerable version and instructions for obtaining and applying the appropriate patches.

Affected IOS versions span from 12.2(60)EZ16 through 15.9(3)M0a. Organizations should upgrade to the latest patched release for their specific hardware platform.

Workarounds

• Implement access control lists (ACLs) to restrict network access to affected devices from untrusted adjacent networks
• Deploy network segmentation to isolate industrial routers from potentially compromised network segments
• Consider implementing 802.1X port-based authentication to limit adjacent network access
• Enable logging and monitoring to detect potential exploitation attempts while awaiting patch deployment

# Example ACL configuration to restrict adjacent network access
# Apply to interfaces facing untrusted network segments
access-list 101 deny udp any host [ROUTER_IP] eq [VDS_PORT]
access-list 101 permit ip any any
interface GigabitEthernet0/0
 ip access-group 101 in