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In early 2024, a new Windows vulnerability came to light: CVE-2024-26207. This flaw impacts the Remote Access Connection Manager (RasMan), a service responsible for managing dial-up and VPN connections. Because so many systems use VPNs and remote access, this issue caught the attention of security experts worldwide.

In this long read, I’ll break down the vulnerability, show what went wrong in simple terms, and use code snippets to help you understand how an attacker could exploit it. At the end, I’ll link official resources and make clear how to stay protected.

What Is RasMan and Why Does It Matter?

RasMan is a core Windows service used for managing connections over the internet, like VPNs or dial-ups. Whenever your computer makes a remote connection, RasMan helps set it up, authenticate, and tear it down. If something in this service is broken, it can leak important info or allow attackers to get a foot in the door.

What Is CVE-2024-26207?

CVE-2024-26207 is an information disclosure vulnerability in Remote Access Connection Manager. This means that an attacker could trick the RasMan service into sharing data it shouldn't—potentially leaking sensitive information or the contents of memory.

Microsoft's official brief is here:
https://msrc.microsoft.com/update-guide/vulnerability/CVE-2024-26207

How Does the Vulnerability Work?

The vulnerability involves how RasMan handles certain requests made from lower-privileged users or processes. If an attacker is able to interact with RasMan in the right way, they can cause it to return memory data that could contain credentials, configuration options, or even fragments of other users' data.

Essentially, RasMan isn't properly checking who is asking for what information, and ends up leaking data.

Exploit Details (Simplified)

To exploit CVE-2024-26207, an attacker must already have limited access to the target system. For example, they might have a regular user account or a foothold via malware. The attacker would then use an API or system call to talk to the RasMan service, asking it for connection details or status, but crafting the request in a way RasMan does not expect.

Here’s a high-level pseudo-code example to demonstrate the basic exploit concept

import ctypes

# The RasMan service exposes APIs like RasEnumEntries
# Attackers can call these with malformed data to extract info

# This is a placeholder example. Real exploitation requires Windows internals knowledge!

rasapi32 = ctypes.windll.rasapi32

def leak_rasman_info():
    buffer = ctypes.create_string_buffer(4096)
    buffer_size = ctypes.c_ulong(len(buffer))
    entries = ctypes.c_ulong()

    # Attempt to enumerate entries (VPNs, dial-ups) with oversized buffer
    ret = rasapi32.RasEnumEntriesW(
        None,      # reserved
        None,      # phonebook
        buffer,    # buffer to receive entries
        ctypes.byref(buffer_size),  # receives buffer size needed
        ctypes.byref(entries)       # receives number of entries
    )

    if ret == :
        print("Success! Data leaked:")
        print(buffer.raw[:buffer_size.value])
    else:
        print("Failed or no info leaked.")

leak_rasman_info()

Note:

Information disclosed could include

- Usernames of VPN/dial-up connections

The easiest way to stay safe is to apply the official Microsoft update.

Direct link to update guide

References

- Microsoft’s Official CVE-2024-26207 Advisory
- Windows Remote Access Connection Manager documentation
- Security researcher writeups—watch for blogs on this issue

Final Thoughts

CVE-2024-26207 reminds us how even core Windows services can have hidden flaws. The risk is greatest in environments where untrusted local accounts are present. An attacker won’t get control of your system with this bug, but information disclosure might let them escalate attacks or move laterally.

Always update your systems and encourage your organization to patch early. If you want to test whether you are vulnerable, use the code snippet above and observe the data returned—but never try these techniques on systems you don’t own!

Timeline

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