CVE-2026-24681: FreeRDP Use After Free Vulnerability

CVE-2026-24681 Overview

CVE-2026-24681 is a Use After Free vulnerability affecting FreeRDP, a free implementation of the Remote Desktop Protocol. Prior to version 3.22.0, asynchronous bulk transfer completions can use a freed channel callback after URBDRC channel close, leading to a use after free condition in the urb_write_completion function. This memory corruption vulnerability can be exploited remotely over the network without requiring authentication.

Critical Impact

This use after free vulnerability in FreeRDP's URBDRC channel handling could allow remote attackers to cause denial of service conditions or potentially achieve code execution through memory corruption when USB redirection is enabled.

Affected Products

• FreeRDP versions prior to 3.22.0
• Systems utilizing FreeRDP's USB device redirection (URBDRC) channel functionality
• Remote Desktop clients and servers implementing the FreeRDP library

Discovery Timeline

• February 9, 2026 - CVE-2026-24681 published to NVD
• February 10, 2026 - Last updated in NVD database

Technical Details for CVE-2026-24681

Vulnerability Analysis

This vulnerability is classified as CWE-416 (Use After Free), a memory corruption flaw that occurs when a program continues to use a pointer after the memory it references has been freed. In FreeRDP's URBDRC (USB Redirection) channel implementation, asynchronous bulk USB transfer completions may reference channel callbacks that have already been freed during channel closure. This race condition between the channel close operation and pending USB transfer completions creates a window where freed memory can be accessed.

The attack can be conducted remotely over the network without requiring user interaction or prior authentication. The primary impact is on system availability, potentially causing crashes or service disruption. While the immediate impact is denial of service, use after free conditions can sometimes be leveraged for more severe exploitation including arbitrary code execution, depending on heap state and exploit sophistication.

Root Cause

The root cause lies in the improper lifecycle management of USB transfer callbacks in the URBDRC channel. When the channel is closed, pending asynchronous USB transfers are not properly cancelled before the channel callback structures are freed. This creates a race condition where completion handlers for in-flight transfers attempt to use deallocated callback structures, resulting in undefined behavior including potential crashes or memory corruption.

Attack Vector

An attacker could potentially trigger this vulnerability by:

1. Establishing a remote desktop connection to a vulnerable FreeRDP server with USB redirection enabled
2. Initiating USB device redirection and triggering bulk USB transfers
3. Timing the channel closure to coincide with pending transfer completions
4. Exploiting the race condition to cause memory access violations

The network-based attack vector allows remote exploitation without requiring local access to the target system.

// Security patch from FreeRDP commit 414f701
// Source: https://github.com/FreeRDP/FreeRDP/commit/414f701464929c217f2509bcbd6d2c1f00f7ed73

 		const uint8_t devNr = idev->get_dev_number(idev);
 
 		pdev->status |= URBDRC_DEVICE_CHANNEL_CLOSED;
+		pdev->iface.cancel_all_transfer_request(&pdev->iface);
 		urbdrc->udevman->unregister_udevice(urbdrc->udevman, busNr, devNr);
 	}
 }

The patch ensures that all pending USB transfer requests are cancelled via cancel_all_transfer_request() before the device is unregistered, preventing completion handlers from accessing freed memory.

Detection Methods for CVE-2026-24681

Indicators of Compromise

• Unexpected crashes or segmentation faults in FreeRDP processes, particularly in URBDRC-related functions
• Core dumps containing references to urb_write_completion or URBDRC channel handling code
• Anomalous network traffic patterns indicating USB redirection channel manipulation
• Memory corruption artifacts in FreeRDP service logs

Detection Strategies

• Monitor FreeRDP process stability and collect crash reports for analysis
• Implement runtime memory corruption detection tools (ASAN, Valgrind) in development and testing environments
• Deploy network intrusion detection rules to identify suspicious RDP traffic with USB redirection activity
• Review system logs for FreeRDP process termination events with SIGSEGV or SIGABRT signals

Monitoring Recommendations

• Enable verbose logging for FreeRDP URBDRC channel operations to track USB redirection activity
• Set up automated alerting for FreeRDP service crashes or unexpected restarts
• Monitor memory usage patterns for FreeRDP processes to detect potential exploitation attempts
• Implement endpoint detection and response (EDR) capabilities to identify memory corruption attacks

How to Mitigate CVE-2026-24681

Immediate Actions Required

• Upgrade FreeRDP to version 3.22.0 or later immediately
• If upgrade is not immediately possible, consider temporarily disabling USB device redirection (URBDRC) functionality
• Implement network segmentation to limit exposure of systems running vulnerable FreeRDP versions
• Review and restrict remote desktop access to trusted networks and authenticated users only

Patch Information

The vulnerability is fixed in FreeRDP version 3.22.0. The security patch is available through the FreeRDP GitHub Security Advisory. The specific fix can be reviewed in commit 414f701, which adds proper cancellation of all USB transfer requests before channel closure.

Workarounds

• Disable URBDRC (USB Redirection) channel in FreeRDP configurations if not required for operations
• Use network firewall rules to restrict RDP connections to trusted IP addresses only
• Deploy application-level firewalls or proxies to inspect and filter RDP traffic
• Consider using alternative remote desktop solutions while awaiting patch deployment

# Configuration example - Disable USB redirection in FreeRDP
# Add the following to FreeRDP client configuration or command line

# Disable dynamic virtual channels including URBDRC
xfreerdp /v:server /u:user -urbdrc

# Or explicitly disable USB redirection
xfreerdp /v:server /u:user /usb:disable