CVE-2026-24683: FreeRDP Use After Free Vulnerability

CVE-2026-24683 Overview

CVE-2026-24683 is a Use After Free vulnerability in FreeRDP, a free implementation of the Remote Desktop Protocol. The vulnerability exists in the ainput_send_input_event function, which caches channel_callback in a local variable and later uses it without proper synchronization. A concurrent channel close operation can free or reinitialize the callback, leading to a use after free condition that can be exploited remotely over the network.

Critical Impact
Remote attackers can exploit this race condition vulnerability to cause denial of service conditions by triggering a use after free through concurrent channel close operations.

Affected Products

FreeRDP versions prior to 3.22.0
Systems using FreeRDP for Remote Desktop Protocol connections
Applications integrating FreeRDP client libraries

Discovery Timeline

2026-02-09 - CVE-2026-24683 published to NVD
2026-02-10 - Last updated in NVD database

Technical Details for CVE-2026-24683

Vulnerability Analysis

This Use After Free vulnerability (CWE-416) stems from a race condition in FreeRDP's ainput channel handling. The ainput_send_input_event function stores a reference to channel_callback in a local variable without implementing proper thread synchronization. When a concurrent channel close operation occurs, the callback memory can be freed or reinitialized while the function still holds a stale reference to it.

The vulnerability is exploitable over the network without requiring authentication or user interaction. Successful exploitation leads to denial of service by crashing the FreeRDP client through memory corruption. The lack of synchronization primitives around the callback access creates a Time-of-Check Time-of-Use (TOCTOU) race condition window.

Root Cause

The root cause is the absence of proper locking mechanisms when accessing shared channel_callback data structures in a multi-threaded context. The ainput_send_input_event function reads the callback pointer without holding any lock, while other threads can simultaneously close the channel and free the associated memory.

Attack Vector

The vulnerability can be exploited remotely over a network connection. An attacker would need to trigger specific timing conditions where:

The victim's FreeRDP client initiates an input event via the ainput channel
The callback pointer is cached locally in ainput_send_input_event
A concurrent operation closes the channel, freeing the callback memory
The function attempts to use the now-freed callback, causing a use after free

The security patch introduces a CRITICAL_SECTION lock to synchronize access to the context when updating the listener:

 	AInputClientContext* context;
 	UINT32 MajorVersion;
 	UINT32 MinorVersion;
+	CRITICAL_SECTION lock;
 };
 
 /**

Source: GitHub FreeRDP Commit Update

Detection Methods for CVE-2026-24683

Indicators of Compromise

Unexpected FreeRDP client crashes during RDP sessions
Memory access violation errors in FreeRDP logs related to ainput channel operations
Core dumps showing use after free patterns in ainput_send_input_event or related functions

Detection Strategies

Monitor FreeRDP client processes for abnormal termination events
Implement crash analysis to identify memory corruption signatures consistent with use after free conditions
Deploy endpoint detection rules that flag FreeRDP crashes with memory access violations in the ainput module

Monitoring Recommendations

Enable verbose logging on FreeRDP clients to capture channel close operations and timing anomalies
Monitor network traffic for unusual RDP session patterns that may indicate exploitation attempts
Set up alerting for repeated FreeRDP client crashes across the environment

How to Mitigate CVE-2026-24683

Immediate Actions Required

Upgrade FreeRDP to version 3.22.0 or later immediately
Audit systems for FreeRDP installations and prioritize patching based on exposure
Consider temporarily disabling ainput channel functionality if upgrade is not immediately possible

Patch Information

The vulnerability is fixed in FreeRDP version 3.22.0. The fix introduces a CRITICAL_SECTION lock in the AInputClientContext structure to properly synchronize access when updating the listener, preventing the race condition that enables the use after free.

Patch details are available at:

Workarounds

Restrict network access to systems running vulnerable FreeRDP versions
Implement network segmentation to limit exposure of RDP clients to untrusted networks
Monitor for and block suspicious RDP traffic patterns at network boundaries

bash

# Check FreeRDP version on Linux systems
xfreerdp --version

# Update FreeRDP to patched version on Debian/Ubuntu
sudo apt update && sudo apt install freerdp2-x11

# For systems using compiled FreeRDP, rebuild from patched source
git clone https://github.com/FreeRDP/FreeRDP.git
cd FreeRDP && git checkout 3.22.0
cmake -B build && cmake --build build && sudo cmake --install build