CVE-2025-26645 - Exploiting Relative Path Traversal in Remote Desktop Client for Remote Code Execution

A new high-severity vulnerability—CVE-2025-26645—has been discovered in popular Remote Desktop Client software. This flaw allows attackers anywhere on your network to execute arbitrary code on your computer. Worse, they don’t even need to log in or have special access. Here’s what you need to know, including code snippets on how this attack works, links to references, and practical details for both defenders and curious hackers.

What is CVE-2025-26645?

CVE-2025-26645 is a “relative path traversal” bug found in the way Remote Desktop Clients (many based on open source code) handle resource files, plugins, or dynamic libraries submitted by a server. A remote attacker can trick the client into loading a malicious file from an attacker-chosen directory, leading to arbitrary code execution—effectively, the attacker gets to run programs on your computer just by having you *connect* to their malicious server.

How the Exploit Works

This vulnerability is rooted in poor validation of file paths. Instead of only allowing safe, expected paths, the client accepts paths like ../malicious.dll—which points *outside* the folder where resources are supposed to be loaded, reaching other places on the drive.

Attacker sets up a fake RDP server and prepares malicious plugin or library files.

2. When a victim connects to that server, the server tells the RDP client to fetch a resource—with a sneaky path (../evil.dll).
3. The client, failing to sanitize the path, loads and runs the malicious file, which may contain any code at all, such as a reverse shell or ransomware.

Example Code Snippet

Below is a *conceptual Python snippet* showing how unsafe path handling might look, and how it can be exploited:

# Vulnerable code: Resource extraction in Remote Desktop Client
def extract_plugin(plugin_path):
    # Suppose received from the server: plugin_path = "../malicious.dll"
    open_path = os.path.join(client_plugins_dir, plugin_path)
    with open(open_path, "rb") as f:
        data = f.read()
    # ...load plugin (dangerous if not checked!)

# Attacker can make the client call:
extract_plugin("../evil.dll")  # This path points OUTSIDE the safe directory!

Why is this bad?
If plugin_path is controlled by an attacker, they can fetch and run any file the user can access—or even drop new ones if the client allows downloading plugins.

Exploit Proof-of-Concept

Many Remote Desktop Clients allow plugin downloads via encrypted RDP messages. Here's a *basic outline* of how you might trigger the vulnerability from a malicious server:

# Attacker's malicious RDP server logic (pseudocode)
def send_malicious_plugin_request(connection):
    # Craft a resource request with the bad path
    resource_message = {
        "plugin": "../evil.dll"  # Relative path escape
    }
    connection.send(serialize(resource_message))
# When the victim RDP client connects, this triggers code execution via evil.dll

On the client, evil.dll could do anything, such as spawn a shell

// evil.dll - Malicious payload (simplified)
#include <windows.h>
BOOL APIENTRY DllMain(HMODULE hModule, DWORD  ul_reason_for_call, LPVOID lpReserved)
{
    if(ul_reason_for_call == DLL_PROCESS_ATTACH) {
        WinExec("cmd.exe /c echo Hacked by CVE-2025-26645 > C:\\Users\\Public\\hacked.txt", SW_HIDE);
    }
    return TRUE;
}

Mitigation

Patch Immediately!
Check your vendor’s security page for an updated client. Most have fixed this by strictly validating all received paths, disallowing ../ sequences, and ensuring only files inside allowed directories can be loaded.

Manual Workaround:
If you can’t update, block outgoing connections to unknown or untrusted RDP servers. Monitor network traffic for odd connections. For developers, always sanitize file paths before using!

References

- NVD Entry for CVE-2025-26645 (official details, updated as vendors file reports)
- Remote Desktop Client GitHub Releases (check for patched versions)
- Microsoft Security Response Center (search for RDP client advisories)
- OWASP Path Traversal Cheat Sheet (background on path traversal risks)

Conclusion

CVE-2025-26645 is a critical security risk for anyone using Remote Desktop software. All it takes is connecting to a bad server, and an attacker could gain control of your device. Always update your software, beware of unknown RDP servers, and for those building networked applications—never trust file paths sent across the wire!

Timeline

Published on: 03/11/2025 17:16:44 UTC
Last modified on: 04/03/2025 21:15:36 UTC