External risk intelligence

FreeRDP Windows Client Heap Buffer Overflow Via Clipboard Channel

CVE advisorySeverity: CRITICAL (CVSS 9.4)

CVE-2026-67305

The vulnerability exists in the FreeRDP Windows client and requires a user to connect to a malicious RDP server. While the protocol is network-based, the client is typically used for internal connections or connecting to trusted remote endpoints, making arbitrary public internet exposure of the client-side clipboard processing uncommon.

Remote Code Execution

Halo Surface Signal: 2 out of 5 — less likely to be public-facing.

External exposure likelihood

Horizon Alert

Summary of the vulnerability and why it matters

A vulnerability in the FreeRDP Windows client could allow a malicious RDP server to corrupt system memory when a user pastes content, potentially leading to the execution of unauthorized code. This occurs due to improper handling of clipboard data responses.

Client flaw allows server-controlled memory corruption.
Executive leaders should monitor for impact to remote access.
Confirm relevance and exposure; impact is conditional.

Attack Path

How an attacker could exploit the issue

An attacker acting as a malicious RDP server can target users who connect to their server. The vulnerability is in how the client processes file content responses for the clipboard. If the server sends a response larger than expected, it can corrupt memory, potentially allowing the attacker to run code on the user's machine when they paste content.

Entry condition: User connects to a malicious RDP server.
Trigger point: User pastes clipboard content.
Resulting risk: Arbitrary code execution on the client.

Live Threat

Current exploitation, exposure, and threat context

A malicious RDP server could exploit this vulnerability by sending a specially crafted response, leading to a heap buffer overflow in the FreeRDP Windows client's clipboard virtual channel. This could result in remote code execution when a user attempts to paste content.

Client clipboard data could be corrupted.
Malicious RDP server sends oversized data.
Remote code execution is possible.

Operational Fix

Recommended remediation, mitigation, and detection steps

The FreeRDP Windows client's clipboard functionality is susceptible to a heap buffer overflow when interacting with a malicious RDP server. This could lead to remote code execution if a user performs a paste operation. The first practical step is to identify where the FreeRDP client is deployed, assess its exposure to untrusted RDP servers, and then determine the accountable owner for remediation planning.

Ownership: Application or endpoint owners.
Verify: Client exposure to untrusted servers.
Action: Plan remediation or user-driven updates.

Supplementary metadata

CVSS vector

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Frequently asked questions

What is FreeRDP?

FreeRDP is an open-source implementation of the Remote Desktop Protocol (RDP). It enables users to connect to remote Windows environments or servers. This specific vulnerability affects the Windows client version used to facilitate these connections, specifically impacting how the software manages data transferred via the clipboard.

What does CWE-122 mean for CVE-2026-67305?

CWE-122 refers to a heap-based buffer overflow. In this context, it means the FreeRDP client fails to verify the size of data sent by a remote server before copying it into memory. Because the software does not check if the server-provided data exceeds the allocated buffer space, it can corrupt adjacent memory, which might allow an attacker to execute unauthorized code.

How is this vulnerability triggered?

An attacker must first convince a user to connect to a malicious RDP server. The vulnerability does not trigger automatically upon connection; it requires the user to perform a paste operation. When the client attempts to process the clipboard file content response from the server, the flaw is triggered if that response contains an oversized data payload.

Is my system at risk?

Halo Surface Signal indicates that while this is a network-based issue, active exploitation requires a user to interact with a malicious server. Because FreeRDP is most commonly used for controlled, internal connections or to reach known, trusted endpoints, arbitrary public internet exposure is less common. Risk is highest if your users connect to untrusted or third-party RDP hosts.

Do I need to patch FreeRDP immediately?

Your first step should be to inventory where FreeRDP is deployed across your systems. Once you have identified which endpoints use the software, assess whether those users frequently connect to untrusted remote environments. Prioritize patching for systems with broader or less-vetted remote access needs, and coordinate with the relevant application owners to plan the update.

References

Written by Nicholas Merritt

Nicholas Merritt is VP of Security Solutions at Halo Security. With more than 25 years across application security, vulnerability prioritization, and offensive security, he helps teams translate threat data into practical exposure validation and remediation focus. He authors Halo Threat Intelligence CVE advisories using Halo Surface Signal and H/A/L/O context to prioritize internet-facing risk.