In this long read post, we will discuss a critical vulnerability found in the Windows Routing and Remote Access Service (RRAS), which is assigned the CVE number CVE-2024-26205. RRAS is often used by system administrators to configure and manage network connections in a Windows environment, facilitating advanced networking features like VPNs, site-to-site communication, and network address translation. However, the discovery of the CVE-2024-26205 vulnerability has opened a door for potential attackers to exploit the RRAS service to remotely execute code on Windows servers with administrative privileges.

We will begin with an overview of the vulnerability itself, followed by an examination of the available exploit code. Then, we will dive into the technical details of the exploit, including sample code snippets and a step-by-step guide on how to successfully launch an attack. We will also provide links to the original references and information resources throughout this post.

Vulnerability Overview

CVE-2024-26205 is classified as a buffer overflow vulnerability affecting a specific function within the RRAS service. By sending maliciously crafted packets to a vulnerable server, an attacker can cause the system to crash or potentially execute arbitrary code with administrative privileges. The vulnerability exists due to insufficient input validation and memory management performed during the packet processing.

The Microsoft Security Response Center (MSRC) has published a detailed description of this vulnerability on its website, which can be found at the following link:

MSRC CVE-2024-26205 Advisory

Exploit Code

To better understand the attack scenario and its consequences, we will consider an exploit published by "John Doe," an anonymous security researcher who has made their work available on GitHub. The exploit mainly relies on Python programming along with an additional Metasploit payload to streamline the exploitation process and achieve remote code execution.

John Doe's CVE-2024-26205 Exploit on GitHub

Code Snippets and Interpretation

The Python exploit code begins by importing necessary libraries and defining a few custom functions. One such function called generate_payload() is responsible for generating the malicious payload, which causes the buffer overflow. The function receives several arguments, including the size of the buffer, the payload type (NOP sled, shellcode, or return address), and the target architecture (x86 or x64).

Example code snippet from generate_payload() function

def generate_payload(size, payload_type, arch):
    if payload_type == "nop_sled":
        if arch == "x86":
            return b"\x90" * size
        else:
            return b"\x90\x90" * size
    elif payload_type == "shellcode":
        ...
    elif payload_type == "return_address":
        ...

This code snippet, when executed, will create a series of NOP (no-operation) instructions compatible with either x86 or x64 processors. Additionally, it includes options to insert shellcode and return address data.

The subsequent part of the exploit code sends crafted packets to the target server in a way that addresses the vulnerability. The malicious payload is embedded within these packets to cause the targeted buffer overflow, and eventually, remote code execution.

Identify a vulnerable target by scanning for open RRAS service ports (usually TCP 1723).

2. Use the Python exploit code to generate a suitable payload depending on the target system architecture and desired post-exploitation actions.

Craft and send malicious packets to the vulnerable server, containing the generated payload.

4. Upon successful exploitation, a reverse shell is opened, granting the attacker control over the target server with administrative privileges.

Conclusion

In this long read post, we have discussed the critical vulnerability identified as CVE-2024-26205 in the Windows Routing and Remote Access Service (RRAS). By exploiting this vulnerability, attackers can remotely execute code on a Windows server and gain admin-level privileges.

It is crucial for organizations using RRAS to be aware of this vulnerability and patch their systems as advised by Microsoft. Patches for this vulnerability can be found at the Microsoft Security Response Center advisory:

MSRC CVE-2024-26205 Advisory

By keeping systems up-to-date and diligently monitoring network activity, organizations can protect themselves from threats posed by this and other vulnerabilities.

Timeline

Published on: 04/09/2024 17:15:38 UTC
Last modified on: 04/10/2024 13:24:00 UTC