CVE-2021-45608: Netgear D7800 Firmware RCE Vulnerability

CVE-2021-45608 Overview

CVE-2021-45608 is a critical integer overflow vulnerability affecting the KCodes NetUSB kernel module used in multiple router devices from D-Link, Edimax, NETGEAR, TP-Link, Tenda, and Western Digital. The vulnerability exists in the SoftwareBus_dispatchNormalEPMsgOut function and can be exploited by an unauthenticated attacker via the WAN interface on TCP port 20005. While remote code execution cannot be ruled out, the exploitation was assessed to be of "rather significant complexity" but not "impossible."

Critical Impact

This integer overflow vulnerability in the KCodes NetUSB kernel module potentially affects millions of end-user routers, allowing unauthenticated attackers to remotely target devices via the WAN interface, potentially leading to complete device compromise.

Affected Products

• NETGEAR D7800 firmware before version 1.0.1.68
• NETGEAR R6400v2 firmware before version 1.0.4.122
• NETGEAR R6700v3 firmware before version 1.0.4.122

Discovery Timeline

• 2021-12-26 - CVE-2021-45608 published to NVD
• 2024-11-21 - Last updated in NVD database

Technical Details for CVE-2021-45608

Vulnerability Analysis

The vulnerability resides in the KCodes NetUSB kernel module, a third-party component widely deployed across consumer routers from multiple vendors. NetUSB provides functionality for sharing USB devices over a network connection. The integer overflow occurs within the SoftwareBus_dispatchNormalEPMsgOut function when processing specially crafted network packets.

The vulnerability is accessible from the WAN interface via TCP port 20005, which significantly increases the attack surface as it exposes affected devices to attacks originating from the internet. The flaw allows an unauthenticated attacker to trigger the integer overflow condition, which could potentially lead to a buffer overflow and subsequent memory corruption.

Root Cause

The root cause is an integer overflow vulnerability (CWE-190) in the SoftwareBus_dispatchNormalEPMsgOut function within the KCodes NetUSB kernel module. When processing input data, the function fails to properly validate size calculations, allowing an attacker to provide values that cause an integer wrap-around. This results in an undersized buffer allocation followed by an out-of-bounds write when the actual data is copied.

Attack Vector

The attack is network-based and requires no authentication or user interaction. An attacker can target the vulnerability by:

1. Sending crafted TCP packets to port 20005 on the WAN interface of an affected device
2. Triggering the integer overflow in the SoftwareBus_dispatchNormalEPMsgOut function
3. Exploiting the resulting memory corruption to potentially achieve code execution

While the vulnerability is remotely accessible, researchers noted that successful exploitation requires overcoming "rather significant complexity," though it is not considered impossible. The kernel-level nature of the vulnerability means successful exploitation could result in complete device compromise with the highest privileges.

The vulnerability mechanism involves crafted network traffic that exploits improper size validation in the NetUSB kernel module. For detailed technical analysis, refer to the SentinelOne CVE-2021-45608 Analysis.

Detection Methods for CVE-2021-45608

Indicators of Compromise

• Unexpected network connections to TCP port 20005 from external IP addresses
• Unusual kernel crashes or router reboots indicating potential exploitation attempts
• Anomalous outbound traffic from the router suggesting post-exploitation activity
• Unexpected modifications to router configuration or firmware

Detection Strategies

• Monitor network traffic for suspicious connections to TCP port 20005, particularly from untrusted sources
• Implement intrusion detection rules to identify malformed NetUSB protocol traffic
• Deploy network segmentation to isolate IoT devices and routers from critical network segments
• Review router logs for authentication failures or unusual administrative activity

Monitoring Recommendations

• Enable logging on edge firewalls to capture connection attempts to port 20005
• Implement network flow analysis to detect anomalous traffic patterns to router devices
• Configure alerts for any WAN-side access attempts to management or service ports
• Regularly audit firmware versions across all network devices to identify vulnerable systems

How to Mitigate CVE-2021-45608

Immediate Actions Required

• Update affected NETGEAR devices to the latest firmware immediately
• Block inbound connections to TCP port 20005 on the WAN interface using firewall rules
• Disable remote management features if not required
• Consider replacing end-of-life devices that will not receive security updates

Patch Information

NETGEAR has released firmware updates to address this vulnerability. Update to the following minimum versions:

• NETGEAR D7800: Firmware version 1.0.1.68 or later
• NETGEAR R6400v2: Firmware version 1.0.4.122 or later
• NETGEAR R6700v3: Firmware version 1.0.4.122 or later

For detailed patch information and download links, refer to the Netgear Security Advisory PSV-2021-0278.

Workarounds

• Block TCP port 20005 on the WAN interface using router ACLs or upstream firewall
• Disable NetUSB/USB over network functionality if not required for your use case
• Place affected devices behind an additional firewall that blocks external access to service ports
• Consider network segmentation to limit the impact of potential compromise

# Example firewall rule to block external access to NetUSB port
# (Implementation varies by device - consult your router documentation)
iptables -A INPUT -i eth0 -p tcp --dport 20005 -j DROP