CVE-2026-24676: FreeRDP Use After Free Vulnerability

CVE-2026-24676 Overview

CVE-2026-24676 is a Use After Free vulnerability in FreeRDP, the free implementation of the Remote Desktop Protocol. The vulnerability exists in the AUDIN (Audio Input) channel subsystem where format renegotiation frees the active format list while the capture thread continues using audin->format, leading to a use after free condition in the audio_format_compatible function. This vulnerability can be exploited remotely over the network without authentication, potentially causing denial of service conditions.

Critical Impact

Remote attackers can trigger a use after free condition in FreeRDP's audio input subsystem, potentially causing application crashes or denial of service without requiring any user interaction or authentication.

Affected Products

• FreeRDP versions prior to 3.22.0
• All platforms running vulnerable FreeRDP client implementations
• Systems utilizing FreeRDP's AUDIN channel for audio input redirection

Discovery Timeline

• 2026-02-09 - CVE-2026-24676 published to NVD
• 2026-02-10 - Last updated in NVD database

Technical Details for CVE-2026-24676

Vulnerability Analysis

This Use After Free vulnerability (CWE-416) occurs in FreeRDP's audio input channel implementation. The flaw manifests when AUDIN format renegotiation occurs - the system frees the active format list through audio_formats_free() while a concurrent capture thread continues to reference audin->format. This creates a classic use after free scenario where the capture thread accesses memory that has already been deallocated.

The vulnerability is exploitable over the network with low attack complexity and requires no privileges or user interaction, making it particularly concerning for exposed RDP clients. The primary impact is on system availability, as successful exploitation leads to memory corruption that can crash the FreeRDP client.

Root Cause

The root cause is a race condition between the format renegotiation logic and the audio capture thread. When the AUDIN channel receives a format renegotiation request, it calls audio_formats_free() to release the current format list. However, the code failed to reset the audin->format pointer to NULL before freeing the formats. This leaves a dangling pointer that the capture thread may continue to dereference, accessing freed memory.

Attack Vector

An attacker can exploit this vulnerability by establishing an RDP connection to a vulnerable FreeRDP client and triggering AUDIN format renegotiation at a precise moment when the audio capture thread is actively using the format data. The attack is network-based and does not require authentication, making it accessible to any attacker who can reach the target system over the network.

// Security patch in channels/audin/client/audin_main.c
// Source: https://github.com/FreeRDP/FreeRDP/commit/026b81ae5831ac1598d8f7371e0d0996fac7db00
 
 	Stream_Seek_UINT32(s); /* cbSizeFormatsPacket */
 
+	audin->format = NULL;
 	audio_formats_free(callback->formats, callback->formats_count);
 	callback->formats_count = 0;

Source: GitHub Commit Update

The fix ensures that audin->format is set to NULL before the formats are freed, preventing the capture thread from accessing freed memory.

Detection Methods for CVE-2026-24676

Indicators of Compromise

• Unexpected FreeRDP client crashes during active RDP sessions with audio input enabled
• Crash dumps indicating memory access violations in audio_format_compatible or AUDIN-related functions
• Unusual AUDIN format renegotiation requests in RDP traffic analysis

Detection Strategies

• Monitor for FreeRDP process crashes and collect crash dumps for analysis of the call stack
• Implement network monitoring to detect anomalous AUDIN channel activity during RDP sessions
• Deploy endpoint detection rules to identify memory corruption patterns in FreeRDP processes

Monitoring Recommendations

• Enable verbose logging for FreeRDP client connections to track AUDIN channel events
• Implement application crash monitoring specifically for FreeRDP client processes
• Configure SentinelOne agents to detect and alert on use after free exploitation patterns in RDP-related processes

How to Mitigate CVE-2026-24676

Immediate Actions Required

• Upgrade FreeRDP to version 3.22.0 or later immediately
• If immediate upgrade is not possible, disable audio input redirection in FreeRDP client configurations
• Review and restrict network access to systems running vulnerable FreeRDP versions

Patch Information

The vulnerability is fixed in FreeRDP version 3.22.0. The fix is available in commit 026b81ae5831ac1598d8f7371e0d0996fac7db00. Organizations should upgrade to the patched version as soon as possible. The security advisory with full details is available at the GitHub Security Advisory GHSA-qh5p-frq4-pgxj.

Workarounds

• Disable AUDIN channel by using the /mic:sys:none or -mic command-line options when launching FreeRDP
• Block or restrict RDP connections from untrusted networks until patching is complete
• Consider using alternative RDP clients that are not affected until FreeRDP can be updated

# Configuration example - Disable audio input redirection in FreeRDP
# Launch FreeRDP without microphone/audio input support
xfreerdp /v:server.example.com /u:username -mic

# Alternative: Explicitly disable audio input
xfreerdp /v:server.example.com /u:username /mic:sys:none