CVE-2026-44799: Remote Desktop Client Buffer Overflow

CVE-2026-44799 Overview

CVE-2026-44799 is a heap-based buffer overflow [CWE-122] in the Microsoft Remote Desktop Client. An unauthorized attacker can execute code over a network when a user connects to an attacker-controlled Remote Desktop Protocol (RDP) server. The vulnerability requires user interaction, since the victim must initiate or accept an RDP connection to a malicious endpoint. Successful exploitation grants the attacker code execution in the context of the RDP client process on the victim machine.

Critical Impact
Remote code execution on client systems that connect to a malicious RDP server, with full impact to confidentiality, integrity, and availability.

Affected Products

Microsoft Remote Desktop Client (see vendor advisory for affected builds)

Discovery Timeline

2026-06-09 - CVE-2026-44799 published to NVD
2026-06-09 - Last updated in NVD database

Technical Details for CVE-2026-44799

Vulnerability Analysis

The flaw is a heap-based buffer overflow within the Remote Desktop Client. The client mishandles the size or layout of data received from a remote RDP server, writing beyond the bounds of a heap-allocated buffer. An attacker who controls the server can craft protocol responses that trigger the overflow during the RDP session setup or data exchange.

Overwriting adjacent heap structures can corrupt object metadata, function pointers, or virtual table pointers used by the client. With reliable heap shaping, the attacker can pivot the corruption into arbitrary code execution in the client process. The high attack complexity reflects the heap grooming and timing required to achieve a stable exploit.

Root Cause

The root cause is improper validation of attacker-supplied length or structure fields before they are used to size a heap copy. This [CWE-122] pattern allows a server-controlled value to drive a copy operation into a buffer that is too small, corrupting the heap.

Attack Vector

Exploitation is network-based but requires user interaction. The victim must connect their Remote Desktop Client to a server that the attacker controls or has compromised. Common delivery mechanisms include phishing links that embed .rdp files, malicious shortcuts, or social engineering that directs a user to connect to a hostile endpoint. Once the session is established, the malicious server returns crafted RDP messages that trigger the overflow.

No public proof-of-concept code is referenced in the advisory. See the Microsoft CVE-2026-44799 Advisory for vendor technical detail.

Detection Methods for CVE-2026-44799

Indicators of Compromise

Outbound RDP connections (TCP/3389 or UDP/3389) from user workstations to untrusted external IP addresses or domains.
Unexpected child processes spawned by mstsc.exe or related Remote Desktop Client binaries.
Execution or download of .rdp files delivered through email, chat, or web downloads.
Crashes or abnormal termination of the Remote Desktop Client process shortly after initiating a session.

Detection Strategies

Hunt for mstsc.exe launching shells, scripting hosts (powershell.exe, cmd.exe, wscript.exe), or LOLBins.
Alert on RDP egress to IP addresses outside approved jump-host or corporate ranges.
Inspect endpoint telemetry for heap corruption indicators such as access violations in the Remote Desktop Client.

Monitoring Recommendations

Log and review .rdp file creations in user download and temp directories.
Correlate process creation events with network connection events from RDP client binaries.
Track Windows Error Reporting and crash dumps tied to the Remote Desktop Client for repeated failures.

How to Mitigate CVE-2026-44799

Immediate Actions Required

Apply the Microsoft security update referenced in the Microsoft CVE-2026-44799 Advisory as soon as it is available in your environment.
Block outbound RDP (TCP/UDP 3389) at the perimeter firewall except to known, sanctioned destinations.
Warn users not to open .rdp files received via email or untrusted web sources.

Patch Information

Microsoft has published guidance and updates through the Microsoft Security Response Center. Refer to the Microsoft CVE-2026-44799 Advisory for the list of affected builds and corresponding patch identifiers, and deploy through Windows Update, WSUS, or your endpoint management platform.

Workarounds

Restrict outbound RDP to an allow-list of internal jump hosts using host firewall rules or group policy.
Use Remote Desktop Gateway to broker connections and prevent direct client-to-server sessions with untrusted endpoints.
Enforce attachment policies that block .rdp files at the email gateway.

bash

# Example: block outbound RDP on Windows endpoints via PowerShell
New-NetFirewallRule -DisplayName "Block Outbound RDP" `
  -Direction Outbound `
  -Protocol TCP `
  -RemotePort 3389 `
  -Action Block

New-NetFirewallRule -DisplayName "Block Outbound RDP UDP" `
  -Direction Outbound `
  -Protocol UDP `
  -RemotePort 3389 `
  -Action Block