CVE-2026-109938: FreeRDP Client DOS Vulnerability

CVE-2026-109938 is a denial of service vulnerability in FreeRDP clients caused by positive mapped-video coordinate overflow. Malicious RDP servers can terminate client connections when video redirection is enabled. This article covers technical details, affected versions, impact assessment, and mitigation strategies.

CVE-2026-109938 Overview

CVE-2026-109938 is an integer overflow vulnerability in FreeRDP, an open-source implementation of the Remote Desktop Protocol (RDP). The flaw affects FreeRDP versions 3.11.0 through versions before 3.32.0 when video redirection is enabled on the client. A malicious or compromised RDP server can send crafted mapped-video geometry coordinates that overflow during processing, causing the FreeRDP client to abort. The issue is tracked under CWE-190: Integer Overflow or Wraparound.

Critical Impact
A compromised or malicious RDP server can forcibly terminate connected FreeRDP clients after a user initiates a session with video redirection enabled, resulting in denial of service.

Affected Products

FreeRDP versions 3.11.0 through versions prior to 3.32.0
FreeRDP client applications with video redirection enabled
Downstream projects and distributions bundling vulnerable FreeRDP builds

Discovery Timeline

2026-10-13 - CVE-2026-109938 published to the National Vulnerability Database (NVD)
2026-10-15 - Last updated in NVD database

Technical Details for CVE-2026-109938

Vulnerability Analysis

The vulnerability resides in the FreeRDP video redirection subsystem, which processes mapped-video geometry updates sent by the RDP server. When the server supplies specific positive coordinate values for the mapped video region, the client performs arithmetic on those coordinates without adequately validating that the result fits within the destination integer type.

The overflow produces an invalid geometry calculation that fails internal sanity checks or triggers an assertion. The client then aborts, severing the active RDP session. Exploitation requires the user to connect to the attacker-controlled server with video redirection enabled, so user interaction is a prerequisite.

The impact is limited to availability. There is no indication the condition yields code execution, information disclosure, or integrity loss on the client host.

Root Cause

The root cause is unchecked arithmetic on attacker-supplied width, height, or offset values in a mapped-video geometry update message. The product of positive coordinates exceeds the range of the integer type used for the computation, producing a wrapped or oversized value that the subsequent code path treats as invalid, leading to process termination.

Attack Vector

The attack vector is network-based and requires an RDP client to initiate a connection to an attacker-controlled server. Once the FreeRDP client negotiates video redirection, the server sends a crafted geometry update packet with coordinates engineered to trigger the overflow. The client aborts after processing the message. Technical specifics are documented in the GitHub Security Advisory GHSA-96rv-gf42-7wq9 and the VulnCheck Advisory on FreeRDP Integer Overflow.

No verified proof-of-concept exploit code is publicly available at this time.

Detection Methods for CVE-2026-109938

Indicators of Compromise

Unexpected termination or crash of FreeRDP client processes (xfreerdp, wlfreerdp, sdl-freerdp) shortly after an RDP session is established.
RDP sessions to untrusted hosts where video redirection channels (tsmf, video) are negotiated.
Core dumps or crash telemetry originating from the FreeRDP video redirection code path.

Detection Strategies

Inventory endpoints and servers running FreeRDP and identify installed versions between 3.11.0 and 3.32.0.
Monitor outbound RDP connections (TCP 3389) from workstations and jump hosts to external or untrusted destinations.
Correlate FreeRDP process crash events with recent RDP session initiation to identify potential exploitation attempts.

Monitoring Recommendations

Enable crash and abort reporting for FreeRDP clients and forward events to centralized logging.
Alert on anomalous outbound RDP traffic from administrative workstations to new or low-reputation hosts.
Track package versions of FreeRDP across the fleet using software inventory tooling and flag versions below 3.32.0.

How to Mitigate CVE-2026-109938

Immediate Actions Required

Upgrade FreeRDP to version 3.32.0 or later on all client systems.
Restrict outbound RDP connections to a known allowlist of trusted servers through firewall or egress policy.
Advise users to avoid connecting to untrusted RDP endpoints until patching is complete.

Patch Information

The vulnerability is fixed in FreeRDP version 3.32.0. Users should update using distribution package managers once the fixed version is available, or build from the upstream release. Refer to the GitHub Security Advisory GHSA-96rv-gf42-7wq9 for commit-level details and backport guidance.

Workarounds

Disable video redirection in the FreeRDP client configuration or omit the /video command-line option when launching sessions.
Limit RDP client usage to connections targeting trusted, administratively controlled servers.
Deploy network segmentation to prevent FreeRDP clients from reaching arbitrary external RDP endpoints.

bash

# Launch xfreerdp without video redirection to avoid the vulnerable code path
xfreerdp /v:trusted-server.example.com /u:username

# Verify installed FreeRDP version meets the fixed release
xfreerdp --version