CVE-2022-23970: Asus RT-AX56U Path Traversal Flaw

CVE-2022-23970 Overview

CVE-2022-23970 is a path traversal vulnerability affecting the ASUS RT-AX56U router's update_json function. The vulnerability exists due to insufficient filtering for special characters in the URL parameter, allowing an unauthenticated attacker on the local network to overwrite system files by uploading malicious files with specific filenames. Successful exploitation can result in service disruption and potential system compromise.

Critical Impact

An unauthenticated LAN attacker can overwrite system files, causing service disruption and potential loss of device availability and integrity.

Affected Products

• ASUS RT-AX56U Firmware version 3.0.0.4.386.45898
• ASUS RT-AX56U Hardware

Discovery Timeline

• April 7, 2022 - CVE-2022-23970 published to NVD
• November 21, 2024 - Last updated in NVD database

Technical Details for CVE-2022-23970

Vulnerability Analysis

This path traversal vulnerability (CWE-22) resides in the update_json function of the ASUS RT-AX56U router firmware. The function fails to properly sanitize special characters within URL parameters, enabling directory traversal sequences to escape the intended file path restrictions. An attacker positioned on the adjacent network can exploit this weakness without authentication to write arbitrary files to system locations.

The vulnerability allows attackers to traverse the file system by injecting directory traversal sequences (such as ../) into URL parameters processed by the update_json function. By crafting malicious requests with path traversal payloads, an attacker can target critical system files and overwrite them with attacker-controlled content.

Root Cause

The root cause of CVE-2022-23970 lies in improper input validation within the update_json function. The function does not adequately filter or sanitize special characters—particularly path traversal sequences—from user-supplied URL parameters before using them in file system operations. This insufficient input validation allows attackers to break out of the intended directory structure and access or modify files in arbitrary locations on the device.

Attack Vector

The attack requires adjacency to the target network (LAN access) but does not require authentication or user interaction. An attacker connected to the same local network as the vulnerable ASUS RT-AX56U router can send specially crafted HTTP requests to the device's web interface. These requests contain malicious URL parameters with path traversal sequences that, when processed by the update_json function, allow the attacker to specify arbitrary file paths.

The exploitation flow typically involves:

1. The attacker identifies an ASUS RT-AX56U router on the local network
2. A crafted HTTP request is sent to the update_json endpoint containing path traversal sequences in the URL parameter
3. The vulnerable function processes the malicious input without proper sanitization
4. The attacker-controlled file content is written to an arbitrary system location, overwriting existing files
5. Service disruption or further compromise occurs depending on which system files are overwritten

For detailed technical information, refer to the TW-CERT Security Advisory.

Detection Methods for CVE-2022-23970

Indicators of Compromise

• Unexpected HTTP requests to the router's web interface containing path traversal sequences (../, ..%2f, etc.) in URL parameters
• Modified or corrupted system configuration files on the ASUS RT-AX56U device
• Unexplained service disruptions or router instability
• Unusual network traffic patterns originating from or directed to the router's management interface

Detection Strategies

• Monitor network traffic for HTTP requests to the ASUS RT-AX56U web interface containing path traversal patterns in URL parameters
• Implement intrusion detection rules to alert on requests to the update_json endpoint with suspicious character sequences
• Review router logs for unusual file access patterns or error messages indicating failed file operations
• Deploy network-based anomaly detection to identify unauthorized access attempts to router management interfaces

Monitoring Recommendations

• Enable comprehensive logging on the ASUS RT-AX56U router if available
• Implement network segmentation to limit exposure of router management interfaces
• Use a security information and event management (SIEM) solution to correlate router logs with network traffic anomalies
• Regularly audit router configuration integrity to detect unauthorized modifications

How to Mitigate CVE-2022-23970

Immediate Actions Required

• Update the ASUS RT-AX56U firmware to the latest available version from ASUS
• Restrict access to the router's management interface to trusted devices only
• Implement network segmentation to isolate the router management network from general user traffic
• Monitor for exploitation attempts using the detection strategies outlined above

Patch Information

ASUS users should check for and apply the latest firmware update for the RT-AX56U router. Visit the official ASUS support website to download the most recent firmware version that addresses CVE-2022-23970. For additional security guidance, refer to the TW-CERT Security Advisory.

Workarounds

• Disable remote management features if not required for your environment
• Implement firewall rules to restrict access to the router's web management interface to specific trusted IP addresses
• Consider deploying a separate network management VLAN to isolate administrative access
• Use a VPN for remote administration instead of exposing the management interface directly

# Example: Restrict management interface access (check router UI for specific options)
# Access the ASUS router web interface at http://router.asus.com
# Navigate to Administration > System
# Set "Enable Web Access from WAN" to "No"
# Apply MAC filtering for LAN management access if available