CVE-2025-26671 - Use After Free Vulnerability in Windows Remote Desktop Services Allows Unauthorized Attackers to Execute Code Over a Network

The recent discovery of the vulnerability CVE-2025-26671 in Windows Remote Desktop Services (RDS) has raised significant concerns for many system administrators and IT professionals. Unauthorized attackers can exploit this use-after-free vulnerability to execute code on a remote system over a network, potentially causing significant damage or leading to the theft of sensitive data. This post will provide an in-depth explanation of the vulnerability, along with code snippets, links to original references, and details on the exploit.

Vulnerability Details

CVE Identifier: CVE-2025-26671
Severity: High
Affected Software: Windows Remote Desktop Services
Impact: Allows unauthorized attackers to execute code on a remote system over a network

Description of the Vulnerability

The use-after-free vulnerability, also known as "dangling pointer," occurs when memory is accessed after it has been freed. This can lead to code corruption, control flow manipulation, and the unauthorized execution of arbitrary code.

In the context of Windows Remote Desktop Services, a specific part of the RDS code improperly handles the use of an earlier freed memory. An attacker can exploit this vulnerability by sending a specially crafted request to a remote system over a network, triggering the use-after-free condition. Once triggered, the attacker can manipulate the system’s memory and potentially execute arbitrary code on the target system.

Code Snippet

The core of the vulnerability lies in the handling of a specific type of message. The following code snippet demonstrates the incorrect handling of a freed memory:

// Sample Code: Simulates the improper handling of freed memory in Windows RDS

void process_request(RemoteRequest* request) {
  // ...
  // Code here processes the request and eventually frees the request object
  // ...
  
  delete request;

  // Later on in the code, "request" is still being accessed, leading to a use-after-free vulnerability
  if (request->is_valid()) {
    process_valid_request(request);
  }

}

Exploit Details

To exploit the vulnerability, an attacker must craft a specially formatted request that triggers the use-after-free condition. The attacker must then send this request to the target RDS system over a network.

Once the request is received, the vulnerability will be triggered, allowing the attacker to manipulate the system's memory and execute arbitrary code. The following snippet demonstrates a potential payload:

// Sample Code: Exploit payload to trigger the use-after-free vulnerability

void craft_and_send_payload(char* target) {
  RemoteRequest* crafted_request = new RemoteRequest(/*...*/);
  
  // Manipulating the request object to trigger the use-after-free on the target system
  // ...

  // Sending the crafted payload to the target system
  send_request_to_target(target, crafted_request);
}

Mitigation and Remediation

To mitigate the risk of this vulnerability, it is recommended that users and administrators apply all available security updates for Windows Remote Desktop Services. Always ensure that systems are running the latest patches to address known security vulnerabilities.

Microsoft has provided a security update for this vulnerability, which can be found at the following link:

https://portal.msrc.microsoft.com/en-us/security-guidance/advisory/CVE-2025-26671

Additionally, limiting exposure to remote connections can also help mitigate the risk of exploitation. Consider using network segmentation and firewalls to restrict access to Remote Desktop Services to only authorized users and systems.

Conclusion

The CVE-2025-26671 vulnerability in Windows Remote Desktop Services presents a notable risk to any organization using these services. By understanding the details of the vulnerability - including the code snippets, original references, and exploit details provided in this post - you can take the proper steps to protect your systems and safeguard sensitive information.

Stay vigilant and ensure your systems are patched and up-to-date to avoid the potential negative impacts of this critical vulnerability.

Timeline

Published on: 04/08/2025 18:15:51 UTC
Last modified on: 04/30/2025 17:14:15 UTC