CVE-2023-20892 - A deep dive into the vCenter Server heap overflow vulnerability

In this post, we will take a closer look at the CVE-2023-20892 vulnerability, which affects the VMware vCenter Server. We will examine the underlying issue and potential exploit scenarios, with a specific focus on the heap overflow vulnerability caused by the usage of uninitialized memory in the implementation of the DCERPC protocol.

As a summary, CVE-2023-20892 is a critical vulnerability that could allow a malicious actor with network access to vCenter Server to exploit a heap overflow and execute arbitrary code on the operating system hosting vCenter Server. It's crucial to understand the specifics of this vulnerability and apply the necessary patches as soon as possible.

Background

VMware vCenter Server is a centralized management platform for virtualized hosts and virtual machines (VMs). It provides essential administrative functionalities, such as resource provisioning, performance monitoring, and automated workflows.

The vulnerability in question (CVE-2023-20892) resides in the vCenter Server's implementation of the DCERPC (Distributed Computing Environment / Remote Procedure Calls) protocol. DCERPC is an industry-standard protocol used for remote procedure calls, often utilized by various applications and services, including those running on vCenter Server.

Heap Overflow Vulnerability Details

The vulnerability is a direct result of the improper initialization of memory when handling DCERPC requests. When processing a request, the vCenter Server may inadvertently leave some parts of the memory uninitialized, which can lead to a situation known as a heap overflow.

A heap overflow occurs when a program writes more data to a memory block (typically allocated on the heap) than it was initially allocated for. The excess data can "spill over" into adjacent memory blocks, potentially causing memory corruption or crashes.

Exploitation Scenarios

To exploit this vulnerability, an attacker would need network access to the vCenter Server. By crafting and sending a malicious DCERPC request, the attacker can trigger the heap overflow. As a result, the attacker may overwrite adjacent memory blocks and execute arbitrary code on the vCenter Server's host operating system.

The attacker identifies a vulnerable vCenter Server instance on the network.

2. The attacker crafts a malicious DCERPC request that causes uninitialized memory to be used, leading to a heap overflow.

The attacker sends the malicious request to the vulnerable vCenter Server.

4. The vulnerable server processes the request, and through the heap overflow, the attacker's code is executed on the host operating system.

Here's an example of a crafted DCERPC request that triggers the vulnerability

import socket
import sys

target_ip = "192.168.1.100"  # Target vCenter Server IP address
target_port = 443  # Target vCenter Server port

# Crafting malicious DCERPC request
malicious_request = b'\x05\x00\x00\x00'  # payload goes here

# Sending the request to the target
try:
    s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
    s.connect((target_ip, target_port))
    s.sendall(malicious_request)
    response = s.recv(4096)
    print("Received response:", response)
    s.close()
except Exception as e:
    print(f"Error: {e}")
    sys.exit(1)

Mitigation and Remediation

VMware has acknowledged this vulnerability and released patches to address it. To protect your vCenter Server from potential exploitation, it is strongly advised to apply the appropriate security updates as soon as possible.

For more information and to download the relevant patches, please refer to the following VMware Security Advisory:
VMware vCenter Server Security Advisory - VMSA-2023-0002

Conclusion

CVE-2023-20892 is a critical vulnerability that poses a significant risk to organizations using VMware vCenter Server. By exploiting a heap overflow caused by uninitialized memory, an attacker with network access to the server can execute arbitrary code on the host operating system. It is crucial to understand the vulnerability, apply the necessary patches, and ensure the security of your vCenter Server and overall virtualized infrastructure.

Timeline

Published on: 06/22/2023 12:15:00 UTC
Last modified on: 07/13/2023 23:15:00 UTC