A security vulnerability classified as CVE-2023-27533 has been discovered in curl, a popular command-line tool used for transferring data with URLs. The vulnerability, affecting versions prior to 8., exists during communication over the TELNET protocol. If left unaddressed, this vulnerability could permit an attacker to pass maliciously crafted user names and "telnet options" during server negotiation, ultimately allowing arbitrary code execution on the targeted system.

How the Vulnerability Works

When a user connects to a server using the TELNET protocol, the server and client exchange messages to negotiate options, such as username and various TELNET options. A lack of proper input validation within curl allows an attacker to send content and manipulate option negotiation parameters without the application's intent. This, in turn, could enable the attacker to execute arbitrary code on the targeted system.

Exploit Details

In order to exploit this vulnerability, an attacker must take advantage of an application that allows user input. By crafting a malicious username or a set of TELNET options, an attacker could then send these as input to the application. If the server accepts the malicious input, it may result in unauthorized access or code execution on the targeted system.

Code Snippet

This code snippet demonstrates an example of how an attacker could exploit the vulnerability by crafting a malicious username containing arbitrary commands:

import socket

# Set target server and port
target = '' # Replace with the target server IP
port = 23

# Craft a malicious username containing arbitrary commands
malicious_username = "testuser;rm -rf /tmp/*;/bin/sh;"

# Create connection
s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
s.connect((target, port))

# Send malicious username

# Close connection

Original References

- [curl][1] is a popular command-line tool for transferring data with URLs. The vulnerability affects curl versions prior to 8..
- [The TELNET protocol][2] is used for interactive text-based communication between two devices, over a network.
- To learn more about curl options and their corresponding TELNET options, consult the [official curl documentation][3].

Mitigation and Remediation

To mitigate this vulnerability within your system, it is critical to update curl to its latest version, 8. or newer. This version contains security patches addressing this particular CVE. Furthermore, it is strongly recommended to sanitize user input, especially when pertaining to usernames and TELNET options, to prevent potential exploits.

[1]: https://curl.se/
[2]: https://tools.ietf.org/html/rfc854
[3]: https://curl.se/docs/manpage.html


Published on: 03/30/2023 20:15:00 UTC
Last modified on: 04/21/2023 23:15:00 UTC