External risk intelligence

FreeRDP Heap Buffer Overflow Vulnerability.

CVE advisorySeverity: CRITICAL (CVSS 9.3)

CVE-2026-31806

FreeRDP is a client-side implementation of the Remote Desktop Protocol. While the vulnerability is triggered by a malicious server, the software typically runs as a client on end-user systems to connect to internal or controlled RDP environments, rather than serving as a public-facing gateway or internet-exposed service.

Buffer Overflow

Freerdp

before 3.24.0

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 FreeRDP, an open-source Remote Desktop Protocol implementation, could allow a malicious RDP server to overwrite memory. This could potentially lead to security compromise. The main concern is confirming relevance and exposure.

A server could write beyond memory boundaries.
It affects remote desktop connections.
Confirm if FreeRDP is used internally.

Attack Path

How an attacker could exploit the issue

An attacker controlling an RDP server could send specially crafted commands to a vulnerable FreeRDP client. These commands would manipulate bitmap dimensions, exceeding expected limits during processing. This could lead to memory corruption, potentially allowing the attacker to overwrite critical data and gain control.

Vulnerable RDP server connection required.
Crafted commands trigger memory overflow.
Heap corruption, leading to compromise.

Live Threat

Current exploitation, exposure, and threat context

A malicious RDP server could potentially cause a heap buffer overflow by sending crafted bitmap dimensions. This overflow, when combined with controlled pixel data, may allow an attacker to overwrite adjacent memory. This could affect the stability or security of the FreeRDP client application when connected to a specially crafted server.

Affected asset: FreeRDP client application memory.
Exposure: Malicious RDP server sends crafted bitmap data.
Consequence: Application instability or potential memory corruption.

Operational Fix

Recommended remediation, mitigation, and detection steps

This vulnerability in FreeRDP affects systems where it's deployed as an RDP client. The first practical step is to identify all instances of FreeRDP, confirm their reachability and business criticality, and then determine the accountable owner for remediation. Planning should consider risk and potential operational impacts, coordinating with vendors if applicable.

Application owners and infrastructure teams should own this.
Verify FreeRDP client exposure and usage.
Plan updates during maintenance windows.

Supplementary metadata

CVSS vector

Validate whether this threat affects your internet-facing exposure.

Halo Threat Intelligence helps prioritize remediation with Halo Surface Signal and H/A/L/O context. Start exposure validation with a free external attack surface trial.

Free EASM Trial See How Signal Works

Frequently asked questions

What is FreeRDP?

FreeRDP is an open-source software library and client application that enables users to connect to remote desktop environments. It implements the Remote Desktop Protocol (RDP), allowing a client to interact with a Windows or Linux desktop session hosted on a remote server. Developers and organizations often embed FreeRDP into custom applications or use it as a standalone client for virtual desktop infrastructure access.

How does CVE-2026-31806 cause a heap buffer overflow?

The vulnerability involves a failure to check bounds during bitmap processing. When the FreeRDP client receives specific surface commands using the NSCodec format, it fails to verify that the provided width and height fit within memory. This class of weakness, categorized as heap-based buffer overflow (CWE-122) and improper length validation (CWE-131), allows a server to supply dimensions that trigger a memory overflow, potentially corrupting data stored near the buffer.

What must happen to trigger this vulnerability?

To trigger the bug, a user must establish an active RDP connection to a malicious or compromised server that intentionally sends malformed bitmap dimension data. The issue is specific to the handling of NSCodec surface commands; standard, well-formed RDP traffic that adheres to expected surface size constraints will not initiate the memory overflow.

Is my system at risk according to Halo Surface Signal?

Halo Surface Signal assesses this as unlikely to be internet-exposed because FreeRDP operates as a client, not a public-facing service. While the threat requires connecting to a malicious server, the risk depends on where your clients connect. If your internal RDP clients are managed and connect only to known, trusted infrastructure, the practical risk is significantly lower than if clients frequently connect to uncontrolled or untrusted remote servers.

How do I address CVE-2026-31806?

The primary response is to update FreeRDP to version 3.24.0 or later, which includes the necessary bounds checking to prevent this overflow. Start by auditing your environment to locate all systems running FreeRDP. Once identified, prioritize these for patching during your next maintenance window, focusing first on machines that connect to the broadest range of external or untrusted remote servers.

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.