CVE-2026-50504: Remote Desktop Client Info Disclosure Bug

CVE-2026-50504 Overview

CVE-2026-50504 is a buffer over-read vulnerability in the Microsoft Remote Desktop Client. An unauthorized attacker can exploit this flaw to disclose information over a network. Exploitation requires user interaction, typically by convincing a target to connect to an attacker-controlled Remote Desktop server. The weakness is classified under [CWE-126] (Buffer Over-read), where the application reads memory beyond the intended buffer boundary and returns that data to the requester. Successful exploitation exposes confidential in-process memory, which may include sensitive session data, credentials, or protocol state used by the RDP client.

Critical Impact

A network-adjacent attacker can read unintended memory contents from a victim's Remote Desktop Client session, resulting in disclosure of sensitive information without authentication.

Affected Products

• Microsoft Remote Desktop Client (see the Microsoft Security Update Guide for affected builds)

Discovery Timeline

• 2026-07-14 - CVE-2026-50504 published to NVD
• 2026-07-14 - Last updated in NVD database

Technical Details for CVE-2026-50504

Vulnerability Analysis

The vulnerability is a buffer over-read in the Microsoft Remote Desktop Client. The client reads data past the end of an allocated buffer when parsing input received from a remote Remote Desktop Protocol (RDP) server. The over-read exposes adjacent process memory to the attacker-controlled server, producing an information disclosure primitive. Confidentiality is impacted, while integrity and availability are not affected. Exploitation is limited to disclosure and does not by itself yield code execution.

Because the attack vector is network-based with no privileges required, a remote server can attempt exploitation as soon as a client establishes a session. However, the flaw requires user interaction, meaning the victim must initiate a connection to a malicious or compromised RDP endpoint. This aligns with typical social-engineering delivery patterns where victims are lured via .rdp file attachments or crafted links.

Root Cause

The root cause is improper validation of a length or index value during processing of server-supplied protocol data. The client trusts a size field or terminator that extends past the allocated buffer, causing the read to spill into adjacent memory regions. This is a classic [CWE-126] pattern where boundary checks either use attacker-controlled length values or fail to enforce the actual buffer size.

Attack Vector

Exploitation requires a victim to connect the Remote Desktop Client to an attacker-controlled server. The malicious server returns a specifically crafted RDP response that triggers the over-read in the client parser. The server then receives leaked memory contents through subsequent client-to-server protocol messages that echo or reference the over-read data. No authentication on the target system is required, and the attacker never needs to reach the victim over an inbound port.

No verified public proof-of-concept code is available for CVE-2026-50504. For authoritative technical details, refer to the Microsoft Security Update for CVE-2026-50504.

Detection Methods for CVE-2026-50504

Indicators of Compromise

• Outbound RDP (TCP/UDP 3389) connections from user workstations to untrusted or newly registered external hosts.
• Execution of .rdp files delivered via email, chat, or web downloads, especially files signed by unknown publishers.
• mstsc.exe processes spawned by Office applications, browsers, or mail clients rather than by user shell activity.

Detection Strategies

• Correlate mstsc.exe launches with the parent process and the source of the .rdp file to identify social-engineering delivery chains.
• Alert on RDP client connections to destinations outside approved corporate IP ranges or jump host inventories.
• Inspect endpoint telemetry for unusual memory access patterns or crashes in the RDP client process shortly after connection establishment.

Monitoring Recommendations

• Enable process creation and network connection logging on all endpoints and forward events to a centralized analytics platform.
• Baseline normal RDP client destinations per user role and flag deviations for review.
• Monitor Microsoft Defender and vendor patch state to confirm the July 2026 update covering CVE-2026-50504 is installed.

How to Mitigate CVE-2026-50504

Immediate Actions Required

• Apply the Microsoft security update referenced in the Microsoft Security Update Guide for CVE-2026-50504 to all Windows endpoints and servers running the Remote Desktop Client.
• Restrict outbound RDP connectivity at the perimeter firewall to only approved internal jump hosts and known third-party destinations.
• Train users to avoid opening .rdp files from untrusted sources and to verify server hostnames before authenticating.

Patch Information

Microsoft has published a security update addressing CVE-2026-50504. Administrators should consult the Microsoft Security Update Guide for the list of affected products, build numbers, and knowledge base article identifiers. Deploy the update through Windows Update, WSUS, Microsoft Intune, or Configuration Manager according to organizational patch policy.

Workarounds

• Block outbound TCP and UDP port 3389 at egress points where users have no business need to reach external RDP servers.
• Enforce Group Policy or Attack Surface Reduction rules that prevent mstsc.exe from launching in response to files originating from email or the internet zone.
• Require RDP connections to traverse an authenticated Remote Desktop Gateway, limiting exposure to attacker-controlled endpoints.

# Example: block outbound RDP from workstations using Windows Defender Firewall
New-NetFirewallRule -DisplayName "Block Outbound RDP" `
  -Direction Outbound `
  -Protocol TCP `
  -RemotePort 3389 `
  -Action Block `
  -Profile Any