CVE-2022-25595: Asus RT-AC86U Firmware DOS Vulnerability

CVE-2022-25595 Overview

CVE-2022-25595 is a denial of service vulnerability affecting the ASUS RT-AC86U router. The vulnerability stems from improper user request handling, which allows an unauthenticated attacker on the local network (LAN) to cause a denial of service by sending specially crafted requests that trigger a server-to-client reply attempt. This improper input validation flaw (CWE-20) can disrupt network services for all devices relying on the affected router.

Critical Impact

An unauthenticated attacker on the adjacent network can cause complete denial of service to the ASUS RT-AC86U router, potentially disrupting network connectivity for all connected devices without requiring any user interaction or authentication.

Affected Products

• ASUS RT-AC86U Firmware version 3.0.0.4.386.45956
• ASUS RT-AC86U Hardware

Discovery Timeline

• 2022-04-07 - CVE-2022-25595 published to NVD
• 2024-11-21 - Last updated in NVD database

Technical Details for CVE-2022-25595

Vulnerability Analysis

This vulnerability exists in the ASUS RT-AC86U router's request handling mechanism. The router fails to properly validate and sanitize incoming user requests, allowing malformed or malicious packets to trigger unexpected behavior in the server-to-client reply functionality. When exploited, this improper input validation causes the device to enter a state where it can no longer serve legitimate network requests, effectively creating a denial of service condition.

The attack requires the attacker to be on the same local area network (adjacent network) as the target router. While this limits the attack surface compared to remotely exploitable vulnerabilities, it remains a significant threat in shared network environments such as offices, public networks, or compromised IoT ecosystems where an attacker may gain LAN access.

Root Cause

The root cause is improper input validation (CWE-20) in the ASUS RT-AC86U firmware's request handling component. The firmware does not adequately validate incoming requests before processing them, allowing specially crafted packets to cause unintended behavior in the server-to-client reply mechanism. This lack of proper boundary checking and input sanitization allows attackers to send requests that the router cannot properly handle, leading to service disruption.

Attack Vector

The attack vector requires adjacent network access, meaning the attacker must be connected to the same local network as the vulnerable router. The attack does not require authentication or user interaction, making it exploitable by any device on the LAN. An attacker would craft specific malicious requests targeting the router's request handling functionality. When these packets are processed, they trigger improper server-to-client reply attempts that result in denial of service.

The attack can be launched from any device connected to the network, including potentially compromised IoT devices, guest network segments (if not properly isolated), or through an attacker who has gained physical access to the network. For detailed technical information, see the TW-CERT Security Advisory.

Detection Methods for CVE-2022-25595

Indicators of Compromise

• Unexpected router restarts or service interruptions without apparent cause
• Network connectivity issues affecting all devices connected to the ASUS RT-AC86U
• Unusual traffic patterns or high volumes of malformed requests in router logs
• Router becoming unresponsive to management interface access

Detection Strategies

• Monitor network traffic for anomalous request patterns targeting the router's management interfaces
• Implement network monitoring to detect unusual traffic volumes from specific LAN hosts
• Enable and review router logging to identify repeated failed request attempts
• Deploy network-based intrusion detection systems to flag suspicious LAN traffic patterns

Monitoring Recommendations

• Enable comprehensive logging on the ASUS RT-AC86U router and forward logs to a centralized SIEM
• Set up alerts for router availability and response time degradation
• Monitor for devices sending high volumes of traffic to router management ports
• Implement network segmentation to limit exposure of critical network infrastructure

How to Mitigate CVE-2022-25595

Immediate Actions Required

• Update the ASUS RT-AC86U firmware to the latest available version from ASUS
• Segment the network to limit which devices can directly communicate with the router
• Review and restrict access to router management interfaces
• Monitor network traffic for suspicious activity targeting the router

Patch Information

ASUS users should check for firmware updates through the ASUS support website or the router's built-in update functionality. Refer to the TW-CERT Security Advisory for additional vendor guidance. Ensure the router is running firmware newer than version 3.0.0.4.386.45956 which contains the vulnerable code.

Workarounds

• Implement network segmentation using VLANs to isolate critical network infrastructure from potentially compromised devices
• Restrict physical and wireless access to the network to trusted devices only
• Consider placing the router behind an additional firewall or security appliance that can filter malicious traffic
• Monitor network activity and implement rate limiting where possible to prevent abuse

# Network monitoring configuration example
# Monitor traffic to router management interface
tcpdump -i eth0 -n host 192.168.1.1 -w router_traffic.pcap

# Check current firmware version via SSH (if enabled)
nvram get firmver
nvram get buildno