CVE-2022-23973: Asus RT-AX56U Firmware RCE Vulnerability

CVE-2022-23973 Overview

CVE-2022-23973 is a stack-based buffer overflow vulnerability affecting the ASUS RT-AX56U router's user profile configuration function. The vulnerability stems from insufficient validation of parameter length, allowing an unauthenticated attacker on the local area network (LAN) to execute arbitrary code, perform unauthorized operations, or cause a denial of service condition on the affected device.

Critical Impact

Unauthenticated LAN attackers can achieve arbitrary code execution on affected ASUS RT-AX56U routers, potentially compromising the entire network infrastructure.

Affected Products

• ASUS RT-AX56U Firmware version 3.0.0.4.386.45898
• ASUS RT-AX56U hardware devices

Discovery Timeline

• 2022-04-07 - CVE-2022-23973 published to NVD
• 2024-11-21 - Last updated in NVD database

Technical Details for CVE-2022-23973

Vulnerability Analysis

This vulnerability is classified as CWE-787 (Out-of-bounds Write), specifically a stack-based buffer overflow condition. The flaw exists within the user profile configuration function of the ASUS RT-AX56U router's firmware. When processing user-supplied input, the function fails to properly validate the length of incoming parameters before copying them to a fixed-size stack buffer.

The adjacent network attack vector means an attacker must be positioned on the same local network segment as the target router, which limits exposure but still represents a significant threat in home and small office environments. No authentication is required to exploit this vulnerability, and no user interaction is necessary, making it particularly dangerous for exposed devices.

Root Cause

The root cause of CVE-2022-23973 is insufficient input validation in the user profile configuration handling code. The firmware does not properly verify the length of user-supplied parameters before performing memory copy operations to a stack-allocated buffer. This lack of bounds checking allows an attacker to supply oversized input that overflows the buffer, potentially overwriting critical stack data including return addresses and saved registers.

Attack Vector

The vulnerability is exploitable from the adjacent network (local LAN), requiring the attacker to have network access to the router. The attack does not require any form of authentication or user interaction, making exploitation straightforward once an attacker gains LAN access.

An attacker would craft a malicious request to the user profile configuration function with an oversized parameter value. The excessive input would overflow the stack buffer, allowing the attacker to overwrite the function's return address and gain control of program execution. This can be leveraged to execute arbitrary shell commands with the privileges of the web server process, typically running as root on embedded devices like the RT-AX56U.

The exploitation mechanism involves sending specially crafted HTTP requests to the router's web management interface with parameter values exceeding expected buffer sizes in the user profile configuration handler. For detailed technical information, refer to the Taiwan TW-CERT Advisory.

Detection Methods for CVE-2022-23973

Indicators of Compromise

• Unexpected router reboots or crashes indicating potential exploitation attempts
• Unusual outbound network connections originating from the router
• Modified router configuration settings, particularly in user profile sections
• Suspicious processes or unexpected services running on the router
• Anomalous traffic patterns from the router's management interface

Detection Strategies

• Monitor HTTP traffic to the router's web management interface for unusually long parameter values in POST requests
• Implement network intrusion detection rules to identify buffer overflow patterns targeting the user profile configuration endpoint
• Enable logging on the router and review for crash events or unexpected restarts
• Deploy network segmentation to limit exposure of router management interfaces

Monitoring Recommendations

• Configure alerts for any direct access to router management interfaces from unexpected internal hosts
• Monitor for changes to router firmware or configuration files
• Implement regular firmware version auditing to ensure devices are running patched versions
• Use network traffic analysis to detect anomalous communication patterns from router devices

How to Mitigate CVE-2022-23973

Immediate Actions Required

• Update ASUS RT-AX56U firmware to the latest available version that addresses this vulnerability
• Restrict access to the router's web management interface to trusted hosts only
• Implement network segmentation to isolate router management from general network traffic
• Disable remote management features if not required

Patch Information

ASUS has addressed this vulnerability in firmware updates released after the affected version 3.0.0.4.386.45898. Users should check the ASUS support website for the latest firmware available for the RT-AX56U router and apply updates immediately. For additional information, consult the Taiwan TW-CERT Advisory.

Workarounds

• Configure firewall rules to restrict access to the router's management interface to specific trusted IP addresses
• Disable the web management interface entirely if command-line administration is feasible
• Enable MAC address filtering to limit which devices can communicate with the router's management interface
• Consider placing the router behind an additional firewall with strict access controls

# Example: Restrict management access via iptables (if shell access is available)
# Allow management access only from trusted admin workstation
iptables -A INPUT -p tcp --dport 80 -s 192.168.1.100 -j ACCEPT
iptables -A INPUT -p tcp --dport 80 -j DROP
iptables -A INPUT -p tcp --dport 443 -s 192.168.1.100 -j ACCEPT
iptables -A INPUT -p tcp --dport 443 -j DROP