CVE-2025-26005

Executive Summary

CVE-2025-26005 is a critical, unauthenticated stack buffer overflow vulnerability discovered in the Telesquare TLR-2005KSH router, specifically in firmware version 1.1.4. The flaw resides in the admin.cgi script when processing the setNtp parameter. An attacker can send a specially crafted HTTP request to the vulnerable CGI endpoint, causing a stack-based buffer overflow. This can lead to remote code execution (RCE) with the privileges of the web server (typically root on embedded devices), allowing full compromise of the device. No authentication is required, and no patch is currently available from the vendor. Public proof-of-concept (PoC) code exists, making this a high-priority threat for network defenders.

CVSS Breakdown & Threat Level

While an official CVSS vector is not provided, based on the vulnerability characteristics, the following assessment is made:

• Attack Vector (AV): Network (N) – Exploitable remotely.
• Attack Complexity (AC): Low (L) – No special conditions required.
• Privileges Required (PR): None (N) – No authentication needed.
• User Interaction (UI): None (N) – No user action required.
• Scope (S): Unchanged (U) – The vulnerable component is the router itself.
• Confidentiality (C): High (H) – Full device compromise leads to data exposure.
• Integrity (I): High (H) – Attacker can modify device configuration and firmware.
• Availability (A): High (H) – Attack can cause denial of service or complete device takeover.

Estimated CVSS Score: 9.8 (Critical)

Threat Level: Critical. The combination of remote exploitability, no authentication, and public PoC makes this an extremely dangerous vulnerability for any organization using the Telesquare TLR-2005KSH.

Deep Dive & Mechanics

The vulnerability is a classic stack-based buffer overflow in the CGI binary handling the admin.cgi endpoint. The setNtp parameter is likely copied into a fixed-size stack buffer without proper bounds checking. By providing an input string longer than the allocated buffer, the attacker overwrites adjacent stack memory, including the saved return address and other critical data.

Technical Flow:

1. The attacker sends an HTTP GET or POST request to /cgi-bin/admin.cgi with a long setNtp parameter.
2. The CGI program parses the parameter and uses a vulnerable function (e.g., strcpy, sprintf, or a custom copy routine) to copy the user-supplied data into a stack buffer.
3. The oversized input overwrites the stack frame, corrupting the saved return address.
4. When the function returns, execution jumps to an address controlled by the attacker.
5. The attacker typically uses a ROP (Return-Oriented Programming) chain or shellcode to execute arbitrary commands, such as spawning a reverse shell or adding a backdoor user.

The vulnerability is unauthenticated because the admin.cgi endpoint does not require a valid session or credentials to process the setNtp parameter.

Vulnerable vs. Patched Code

Since no patch is available, a direct code comparison is not possible. However, the vulnerable code pattern is typical of embedded CGI applications:

Vulnerable Code (Conceptual C):

void handle_setNtp(char *input) {
    char buffer[64];
    // VULNERABLE: No bounds checking
    strcpy(buffer, input);
    // ... process NTP settings
}

Patched Code (Conceptual C):

void handle_setNtp(char *input) {
    char buffer[64];
    // SAFE: Use strncpy with length limit
    strncpy(buffer, input, sizeof(buffer) - 1);
    buffer[sizeof(buffer) - 1] = '\0';
    // ... process NTP settings
}

The fix involves replacing unbounded string copy functions with bounded alternatives (e.g., strncpy, snprintf) and ensuring proper null-termination.

Exploitation & Lab Setup

Red Team (Exploitation)

Prerequisites:

• A Telesquare TLR-2005KSH router with firmware 1.1.4 (or a vulnerable emulated environment).
• Network access to the router's web interface (typically port 80 or 443).
• A tool to send crafted HTTP requests (e.g., curl, python, metasploit).

Exploitation Steps:

1. Identify Target: Scan for devices with the default web interface or use Shodan dorks.
2. Craft Payload: Create a buffer overflow payload. The payload structure is:
   • Padding to reach the return address.
   • Overwritten return address pointing to a ROP gadget or shellcode.
   • Shellcode (e.g., MIPS or ARM depending on the router's architecture) to execute a command.
3. Send Exploit: Use a tool like curl to send the malicious request.

Example Exploit (Python):

import socket

def exploit(target_ip, target_port=80):
    # Placeholder for actual payload generation
    # This is a conceptual example
    padding = b"A" * 100  # Adjust offset based on reverse engineering
    return_address = b"\x00\x00\x00\x00"  # Replace with actual address
    shellcode = b"\x00" * 200  # Replace with actual shellcode

    payload = b"setNtp=" + padding + return_address + shellcode

    request = (
        b"GET /cgi-bin/admin.cgi?" + payload + b" HTTP/1.1\r\n"
        b"Host: " + target_ip.encode() + b"\r\n"
        b"Connection: close\r\n\r\n"
    )

    sock = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
    sock.connect((target_ip, target_port))
    sock.send(request)
    response = sock.recv(4096)
    print(response.decode(errors='ignore'))
    sock.close()

if __name__ == "__main__":
    exploit("192.168.1.1")

Note: The actual exploit requires reverse engineering the firmware to determine the exact offset, ROP gadgets, and architecture-specific shellcode.

Blue Team (Defense & Detection)

Detection Strategy:

1. Network Monitoring: Monitor for HTTP requests to /cgi-bin/admin.cgi with an abnormally long setNtp parameter.
2. Anomaly Detection: Baseline normal setNtp parameter lengths (typically < 100 bytes). Flag requests exceeding this threshold.
3. Honeypot: Deploy a decoy Telesquare router to capture exploit attempts.

Mitigation Steps:

1. Isolate Devices: Place the router on a separate VLAN with strict access controls.
2. Web Application Firewall (WAF): Deploy a WAF rule to block requests with setNtp parameters exceeding a reasonable length.
3. Firmware Update: Monitor the vendor's website for a patch. If none is available, consider replacing the device.
4. Disable Remote Management: If not required, disable remote access to the web interface.

Indicators of Compromise (IOCs)

Network IOCs:

• HTTP requests to /cgi-bin/admin.cgi with setNtp parameter length > 200 bytes.
• Outbound connections from the router to unknown IP addresses on non-standard ports (e.g., 4444, 31337).
• Unusual DNS queries from the router.

Host IOCs (on the router):

• Unexpected processes running (e.g., /tmp/.x, /var/run/...).
• Modified or new files in /tmp/ or /var/.
• Changes to the router's configuration (e.g., new admin user, modified DNS settings).
• Log entries showing repeated crashes of the admin.cgi process.

File IOCs:

• Suspicious files in /tmp/ with names like .* (hidden files) or shell.

Detection Engineering

YARA Rule

rule CVE_2025_26005_Exploit_Attempt {
    meta:
        description = "Detects HTTP requests attempting to exploit CVE-2025-26005 in Telesquare TLR-2005KSH"
        author = "Valters IT"
        date = "2025-04-10"
        reference = "CVE-2025-26005"
        hash = "d41d8cd98f00b204e9800998ecf8427e"
    strings:
        $cgi_path = "/cgi-bin/admin.cgi"
        $setNtp_param = "setNtp="
        $long_payload = /setNtp=[A-Za-z0-9%]{200,}/  // Matches payloads >= 200 chars
    condition:
        $cgi_path and $setNtp_param and $long_payload
}

Sigma Rule

title: CVE-2025-26005 Telesquare TLR-2005KSH Stack Overflow Attempt
id: 8a9b7c6d-5e4f-3a2b-1c0d-9e8f7a6b5c4d
status: experimental
description: Detects HTTP requests with an abnormally long setNtp parameter targeting the admin.cgi endpoint.
author: Valters IT
date: 2025-04-10
references:
    - https://nvd.nist.gov/vuln/detail/CVE-2025-26005
logsource:
    category: webserver
    product: apache
    service: http
detection:
    selection:
        cs-uri-query|contains: "/cgi-bin/admin.cgi"
        cs-uri-query|contains: "setNtp="
        cs-uri-query|length: >= 250
    condition: selection
falsepositives:
    - Legitimate long NTP server names (unlikely)
level: high

Suricata Rule

alert http any any -> any any (msg:"CVE-2025-26005 Telesquare TLR-2005KSH Stack Overflow Attempt"; flow:to_server; content:"/cgi-bin/admin.cgi"; http_uri; content:"setNtp="; http_uri; pcre:"/setNtp=[A-Za-z0-9%]{200,}/Ri"; classtype:attempted-admin; sid:1000001; rev:1;)

Remediation & Mitigation

Immediate Actions:

1. Isolate Affected Devices: Disconnect the Telesquare TLR-2005KSH from the internet and place it on an isolated management VLAN.
2. Disable Remote Management: If remote access is not critical, disable the web interface or restrict access to trusted IPs only.
3. Monitor for Exploitation: Deploy the provided detection rules (YARA, Sigma, Suricata) to identify any exploitation attempts.

Long-Term Actions:

1. Vendor Patch: Contact Telesquare for a firmware update. If no patch is released, consider replacing the device with a supported alternative.
2. Network Segmentation: Ensure that all IoT/embedded devices are on a separate network segment with strict egress filtering.
3. Regular Audits: Conduct regular vulnerability scans of network devices and apply patches promptly.

Workaround (if patching is not possible):

• Implement a reverse proxy or WAF that inspects and sanitizes HTTP requests to the vulnerable endpoint.
• Block all HTTP requests containing setNtp in the query string at the network perimeter.

Valters IT