CVE-2026-24680: FreeRDP Use-After-Free Vulnerability

CVE-2026-24680 Overview

CVE-2026-24680 is a Use-After-Free vulnerability in FreeRDP, a free implementation of the Remote Desktop Protocol. Prior to version 3.22.0, the sdl_Pointer_New function frees data on failure, but subsequently pointer_free calls sdl_Pointer_Free and frees the same memory again, triggering a double-free condition that was detected by AddressSanitizer (ASan) as a Use-After-Free. This vulnerability affects the SDL3 client component of FreeRDP and can be exploited remotely over the network.

Critical Impact

Remote attackers can exploit this Use-After-Free vulnerability to cause denial of service conditions through memory corruption, potentially crashing FreeRDP client sessions.

Affected Products

• FreeRDP versions prior to 3.22.0
• FreeRDP SDL3 client implementations
• Systems using FreeRDP for Remote Desktop Protocol connections

Discovery Timeline

• 2026-02-09 - CVE-2026-24680 published to NVD
• 2026-02-10 - Last updated in NVD database

Technical Details for CVE-2026-24680

Vulnerability Analysis

This Use-After-Free vulnerability (CWE-416) occurs in the SDL3 pointer handling code within FreeRDP's client implementation. The flaw manifests when memory allocated for pointer data is freed during error handling in sdl_Pointer_New, but the pointer variable is not reset to null. Subsequently, when pointer_free invokes sdl_Pointer_Free, the code attempts to free the already-released memory, resulting in undefined behavior.

Use-After-Free vulnerabilities are particularly dangerous because they can lead to memory corruption, program crashes, and in some scenarios, arbitrary code execution. The vulnerability is exploitable remotely over the network, requiring no user interaction or authentication, which makes it accessible to unauthenticated attackers targeting FreeRDP client sessions.

Root Cause

The root cause is improper memory management in the sdl_pointer.cpp file within the SDL3 client code. When sdl_Pointer_New encounters a failure condition, it correctly frees the allocated memory using winpr_aligned_free(ptr->data), but fails to set ptr->data to nullptr. This leaves a dangling pointer that is later accessed and freed again by the cleanup routine, causing the Use-After-Free condition.

Attack Vector

The attack vector is network-based, allowing remote exploitation without requiring authentication or user interaction. An attacker could potentially craft malicious RDP session data that triggers the error condition in pointer handling, causing the double-free scenario. This would result in denial of service through client crashes.

// Security patch from client/SDL/SDL3/sdl_pointer.cpp
// Source: https://github.com/FreeRDP/FreeRDP/commit/c42ecbd183b001e76bfc3614cddfad0034acc758

 	        &context->gdi->palette))
 	{
 		winpr_aligned_free(ptr->data);
+		ptr->data = nullptr;
 		return FALSE;
 	}

The fix ensures that after freeing the pointer data, it is immediately set to nullptr, preventing the subsequent double-free when cleanup routines attempt to free the memory again.

Detection Methods for CVE-2026-24680

Indicators of Compromise

• Unexpected FreeRDP client crashes during RDP sessions
• Memory corruption errors or segmentation faults in FreeRDP processes
• AddressSanitizer (ASan) reports indicating Use-After-Free conditions in SDL pointer functions
• Abnormal RDP connection terminations without user initiation

Detection Strategies

• Monitor FreeRDP client processes for unexpected terminations or crash dumps
• Deploy memory debugging tools like AddressSanitizer on development and testing systems to detect UAF conditions
• Implement logging for FreeRDP client session failures and analyze patterns
• Use endpoint detection solutions to identify crash signatures associated with this vulnerability

Monitoring Recommendations

• Enable detailed logging for FreeRDP client applications to capture error conditions
• Monitor system logs for repeated crashes of FreeRDP processes
• Configure crash reporting mechanisms to collect and analyze FreeRDP client failures
• Track network connections to RDP endpoints for suspicious activity patterns

How to Mitigate CVE-2026-24680

Immediate Actions Required

• Upgrade FreeRDP to version 3.22.0 or later immediately
• Review deployment environments for affected FreeRDP versions
• Temporarily disable FreeRDP SDL3 clients if upgrade is not immediately possible
• Implement network segmentation to limit exposure of vulnerable FreeRDP clients

Patch Information

FreeRDP has released version 3.22.0 which includes the fix for this vulnerability. The patch adds a critical null pointer assignment after memory deallocation to prevent the double-free condition. Organizations should apply this update as soon as possible.

The specific fix can be reviewed in the GitHub commit c42ecbd. Additional details are available in the GitHub Security Advisory GHSA-j893-9wg8-33rc.

Workarounds

• Use alternative RDP clients until patching is complete
• Restrict network access to systems running vulnerable FreeRDP versions
• Monitor FreeRDP client sessions for unusual behavior or crashes
• Consider using the non-SDL client implementations if available and applicable to your environment

# Upgrade FreeRDP to patched version
# For package manager installations:
apt update && apt install freerdp2-x11

# For source installations, build from the patched version:
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