A new, high-impact vulnerability has been discovered: CVE-2025-27480. This dangerous bug is a _use-after-free_ issue in the Remote Desktop Gateway (RD Gateway) Service. The flaw lets an attacker execute their own code on a target machine—without needing to log in—by sending specially crafted network traffic.

If your organization uses Microsoft Remote Desktop Services (RDS) and exposes RD Gateway to the internet, this CVE should have your full attention. This post explains in plain English _what’s vulnerable, how the bug works, and how attackers might exploit it_. We’ll also show an example snippet to help you recognize the issue and point to official advisories and technical write-ups.

What is Remote Desktop Gateway?

RD Gateway lets you securely connect to remote Windows desktops and servers over the Internet. It wraps Remote Desktop Protocol (RDP) inside HTTPS, allowing RDP communications to go through firewalls securely.

However, any bug granting attackers code execution on this service exposes your internal network to takeover.

What’s a Use-After-Free?

A _use-after-free_ happens when a program tries to use memory after it has been freed (released). This stale pointer can be exploited by attackers to trick the program into running malicious code. In the context of a networked service like RD Gateway, this means an external party can send data, trigger the bug, and potentially run their own programs on your server.

How CVE-2025-27480 Works

In vulnerable versions of RD Gateway, there’s a flaw in the way the gateway processes certain types of incoming requests. If an attacker sends specially crafted packets during the handshake phase, the server frees a chunk of memory but continues using the pointer. A quick attacker can prime that stale memory with their own data, hijacking the flow of the program.

Code Snippet: Example Vulnerable Logic (Pseudocode)

Here’s a simplified pseudocode, _not the actual source code_, to illustrate how this vulnerability can occur:

// Vulnerable Pseudocode

struct Session {
    char* data;
    // Other fields...
};

void handle_session(Session* s) {
    free(s->data);               // Free memory
    if (special_condition(s)) {
        // Still tries to use freed memory!
        process(s->data);        // Use-after-free: potential hijack
    }
}

If an attacker controls the timing (e.g., special packets, as in CVE-2025-27480), they can take over the data pointer and direct the server’s next action.

Proof-of-Concept Exploit Walkthrough

While we won’t share weaponized exploit code, the public research community reports steps like these:

Heap Manipulation: Injects payload data to overlap freed memory.

4. RCE: The gateway, running as a high-privilege process, executes attacker instructions—often opening a remote shell.

> Note: The attack requires _no user interaction_ and _no credentials_. A single malicious packet can be enough.

- Microsoft Security Advisory for CVE-2025-27480
- Rapid7 Analysis of RD Gateway Use-After-Free
- ZDI Blog on Remote Desktop Exploits
- Common Vulnerabilities and Exposures

Apply Microsoft’s official patch for all affected RD Gateway servers ASAP.

2. Restrict access to RD Gateway from only trusted IPs—never expose to the open Internet if possible.

Final Word

CVE-2025-27480 is another wake-up call about the dangers of exposing critical infrastructure with insufficient patching or monitoring. If you’re running RD Gateway, stop what you’re doing and patch now. Attackers can and will scan for this vulnerability.

Stay safe!

*This write-up was made exclusively for this conversation. For technical deep-dive or hands-on analysis, refer to the linked advisories and go straight to Microsoft’s patch resources.*

Timeline

Published on: 04/08/2025 18:15:58 UTC
Last modified on: 04/30/2025 17:14:23 UTC