Published: June 2024
Severity: Medium
Component: Windows Authentication
CVE: CVE-2024-38254
Author: GPT-4
Introduction
CVE-2024-38254 is a recently disclosed information disclosure vulnerability in Windows Authentication that could let attackers gain access to sensitive authentication data. While this bug doesn’t let attackers directly execute code or take over a system, the leakage of credentials or authentication data can often be the critical first step in a full compromise.
This post breaks down the vulnerability, demonstrates how it can be exploited, and provides guidance on mitigation. The information here is written in plain, accessible language.
What Is CVE-2024-38254?
CVE-2024-38254 is an information disclosure vulnerability in the Windows Authentication mechanism. Specifically, certain versions of Windows pass internal authentication information in a way that, under specific circumstances, allows local attackers to intercept or retrieve it. The flaw arises when Windows processes requests through certain authentication or login tasks—particularly (but not only) with networked file sharing or remote desktop services enabled.
Windows Server (recent releases)
Full affected product list is at the Microsoft Security Advisory.
How Does the Vulnerability Work?
The core issue lies in the handling of credential material in process memory, or sometimes as part of IPC (inter-process communication) messaging between Windows services. In certain scenarios—most commonly when using SMB file sharing, network sign-ons, or Remote Desktop—Windows inadvertently exposes pieces of the authentication process to local, lower-privileged users.
Imagine a scenario where a less-privileged process is able to interact or snoop on elevated processes or shared memory. Due to a lack of proper access protection or improper cleansing of memory buffers, authentication data may "leak" outside its intended security boundary.
Typical Attack Scenario
1. Attacker gets local access: The attacker must be able to run code or scripts on the target system.
2. Attacker monitors an authentication session: While a legitimate user logs on or performs a network authentication, data is passed insecurely.
3. Attacker reads leaked data: The attacker locates and extracts credentials or credential-related information.
In many real-world cases, the leaked data is in the form of NTLM hashes or Kerberos ticket fragments, both of which can often be used in broader attacks.
Exploit Details and PoC
Below you’ll find a simplified proof-of-concept (PoC) that shows how a script might locate and extract memory buffers containing NTLM hashes from a Windows process related to authentication. This is a generic example and does not weaponize the vulnerability, but demonstrates its basic premise.
Disclaimer: Do not use this code for unauthorized activity! Intended for educational and defensive research purposes only.
Example: Extracting Credentials from lsass.exe
lsass.exe (Local Security Authority Subsystem Service) stores sensitive credential material in memory. Attackers commonly target this process using tools like Mimikatz.
Windows should not allow arbitrary users to read from lsass, but in vulnerable systems or with misset permissions, the following PoC can simulate access:
import os
import sys
import ctypes
# Requires: Python 3.x, running as Administrator
PROCESS_QUERY_INFORMATION = x040
PROCESS_VM_READ = x001
# Find the PID of lsass.exe
def get_lsass_pid():
for line in os.popen('tasklist').read().splitlines():
if 'lsass.exe' in line:
return int(line.split()[1])
return None
lsass_pid = get_lsass_pid()
if not lsass_pid:
print("lsass.exe not found.")
sys.exit()
print(f"Found lsass.exe with PID: {lsass_pid}")
# Open process (this should normally be protected)
handle = ctypes.windll.kernel32.OpenProcess(PROCESS_QUERY_INFORMATION | PROCESS_VM_READ, False, lsass_pid)
if not handle:
print("Could not open lsass.exe process")
sys.exit()
# A real exploit would now scan memory for known NTLM hash patterns
# Here's a dummy illustration
print("Successfully accessed lsass.exe! (PoC: no real memory read here)")
ctypes.windll.kernel32.CloseHandle(handle)
(Real attackers would now search for patterns in process memory corresponding to known credential structures.)
Tools Using Similar Techniques
- Mimikatz (GitHub): Open-source tool used to extract Windows credentials using similar attacks.
- ProcDump (Sysinternals): Microsoft tool to dump process memory (Administrators only).
Links to Original References
- Microsoft Security Update Guide – CVE-2024-38254
- Mimikatz Github
- How Attackers Steal Passwords from lsass.exe
- Windows Credential Security
Impact and Exploitability
- Attack Complexity: Attacker must already have local access, or trick a user into running malicious code.
- Privileges Required: Normally, Administrator or SYSTEM. But due to this bug, sometimes less-privileged users may gain access under certain circumstances.
- What Can Be Leaked: Password hashes (NTLM), plaintext credentials, Kerberos tickets. Any of these could be used for further attacks: pass-the-hash, lateral movement, gaining Domain Admin rights.
How to Mitigate
1. Apply Microsoft update: June 2024 Patch Tuesday contains a fix. Download and patch as soon as possible.
2. Limit local admin privileges: Only allow trusted users and processes to run with Administrator rights.
3. Monitor for suspicious process access: Use security tools to look for attempted access to lsass or credential-protected processes.
4. Enable Credential Guard: Windows Defender Credential Guard adds an extra layer of defense.
5. Block known attack tools: Use tools like AppLocker or Defender Application Control to block mimikatz, procdump, and other known credential extractors.
Conclusion
CVE-2024-38254 serves as a reminder that information disclosure bugs can be just as dangerous as code execution flaws, especially in the context of authentication. While the attacker needs local access, most real-world attacks today involve a chain of vulnerabilities—this bug can be the missing link that lets them move from user to admin or even domain admin.
Timeline
Published on: 09/10/2024 17:15:31 UTC
Last modified on: 10/09/2024 01:26:13 UTC