TFTP/Bittorrent-tracker - Port 69/UDP

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Basic Info

Trivial File Transfer Protocol (TFTP) is one of the simplest file transfer protocols. It operates over UDP port 69, allowing file transfers without the need for user authentication or encryption. TFTP's simplicity makes it efficient for internal network operations, such as deploying configuration files and ROM images to devices like VoIP handsets, but this simplicity also introduces serious security risks.

Key vulnerabilities:

1. No authentication: Anyone with access to a TFTP server can potentially download or upload files.

2. No encryption: Data transferred via TFTP is sent in clear text, meaning attackers can intercept it (e.g., via a man-in-the-middle attack) and view the content.

3. No access controls: TFTP lacks file permission mechanisms, leading to unrestricted access to certain files if proper configurations are not in place.

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Attacker Workflow: How Hackers Exploit TFTP

Below is a step-by-step workflow demonstrating how an attacker could exploit TFTP vulnerabilities.

Enumeration

Once a TFTP server is discovered, the attacker will try to enumerate files on the server. Since TFTP does not allow directory listing, they will rely on brute-forcing known file paths or using tools like tftp-enum to discover sensitive files.

nmap -n -Pn -sU -p69 -sV --script tftp-enum <IP>

Downloading/Uploading Files

After identifying files, you can attempt to download them for analysis or upload malicious files to compromise the system.

Metasploit provides a built-in module for TFTP file transfers:

msf5> auxiliary/admin/tftp/tftp_transfer_util

Python's Tftpy library can be used to download or upload files:

import tftpy
client = tftpy.TftpClient(<ip>, <port>)
client.download("filename in server", "/tmp/filename", timeout=5)
client.upload("filename to upload", "/local/path/file", timeout=5)

These methods allow you to retrieve critical system files, such as configuration files that contain sensitive information, or plant malicious files to be executed by devices relying on TFTP.

Exploitation and Privilege Escalation

The goal of exploitation is to leverage the downloaded files to gain higher privileges or move laterally within the network. For example:

• Configuration files may contain default or hardcoded credentials that give attackers access to other network services (e.g., SSH or Telnet).

• Firmware images can reveal vulnerabilities that attackers can use to re-flash devices with backdoored firmware, effectively compromising the entire device.

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Common CVEs Related to TFTP

Here are some notable CVEs related to TFTP that have been exploited in real-world attacks:

• CVE-2017-14205: This vulnerability affects SolarWinds TFTP Server, a popular TFTP implementation. It allows remote attackers to execute arbitrary code by uploading crafted files. The root of the issue lies in improper file handling, where unchecked file uploads lead to code execution.

• CVE-2010-4652: A buffer overflow vulnerability in the TFTP server of NetBSD. This allowed remote attackers to cause a denial of service (crash) or execute arbitrary code by sending crafted packets to the server.

• CVE-2019-12904: Found in haneWIN TFTP Server, this vulnerability allows an attacker to bypass security measures through directory traversal, giving them access to arbitrary files on the TFTP server.

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BitTorrent Trackers and Port 69: Why Shodan Labels This Port

In certain cases, Shodan identifies port 69 as associated with a BitTorrent tracker. This occurs because some BitTorrent trackers (software that coordinates peer-to-peer file sharing) may also run on UDP-based services, even though it’s uncommon. This could lead to a port conflict or identification error, but attackers could leverage the same reconnaissance tools to discover vulnerable services.