CVE-2026-24682: FreeRDP Buffer Overflow Vulnerability

CVE-2026-24682 Overview

CVE-2026-24682 is a heap-based buffer overflow vulnerability in FreeRDP, a free implementation of the Remote Desktop Protocol. The vulnerability exists in the audin_server_recv_formats function, which incorrectly calculates the number of audio formats to free on parse failure. This miscalculation (i + i instead of the correct value) leads to an out-of-bounds access when audio_formats_free is called, potentially causing a denial of service condition or memory corruption.

Critical Impact

Network-accessible FreeRDP servers prior to version 3.22.0 are vulnerable to remote denial of service attacks through malformed audio format data that triggers heap-based out-of-bounds memory access.

Affected Products

• FreeRDP versions prior to 3.22.0
• Systems running FreeRDP server with audio input redirection enabled
• Applications integrating the FreeRDP library for RDP functionality

Discovery Timeline

• 2026-02-09 - CVE-2026-24682 published to NVD
• 2026-02-10 - Last updated in NVD database

Technical Details for CVE-2026-24682

Vulnerability Analysis

The vulnerability resides in the audio input channel server implementation within channels/audin/server/audin.c. When the server receives and parses audio format data from a client, it iterates through each format structure. If a parse failure occurs during this iteration, the cleanup code attempts to free the already-allocated audio formats. However, the code incorrectly passes i + i (doubling the iterator) to the audio_formats_free function instead of the correct count, causing the function to attempt freeing more memory than was actually allocated.

This heap-based buffer overflow (CWE-122) occurs because the incorrect calculation causes out-of-bounds memory access, reading and potentially corrupting heap memory beyond the allocated buffer boundaries. An attacker can exploit this by sending specially crafted audio format data that causes a parse failure at a strategic point in the iteration, maximizing the out-of-bounds access.

Root Cause

The root cause is a programming error in the error handling path of audin_server_recv_formats. The developer mistakenly used i + i instead of the correct iterator value when calling audio_formats_free upon encountering a parse failure. This arithmetic error doubles the count of formats to free, leading to heap memory corruption when the function attempts to access and free memory beyond the allocated array.

Attack Vector

The attack vector is network-based, requiring no authentication or user interaction. An attacker can connect to a vulnerable FreeRDP server and send malformed audio format data through the audio input redirection channel. When the server attempts to parse this data and encounters the crafted failure condition, the vulnerable cleanup code is triggered, causing out-of-bounds memory access.

The following patch from the FreeRDP security commit shows the fix:

 		AUDIO_FORMAT* format = &pdu.SoundFormats[i];
 
 		if (!audio_format_read(s, format))
-		{
-			WLog_Print(audin->log, WLOG_ERROR, "Failed to read audio format");
-			audio_formats_free(pdu.SoundFormats, i + i);
-			return ERROR_INVALID_DATA;
-		}
+			goto fail;
 
 		audio_format_print(audin->log, WLOG_DEBUG, format);
 	}

Source: GitHub Commit Reference

The fix removes the inline error handling with the incorrect i + i calculation and instead uses a goto fail statement to ensure proper cleanup with the correct iterator count.

Detection Methods for CVE-2026-24682

Indicators of Compromise

• Unexpected crashes or segmentation faults in FreeRDP server processes
• FreeRDP server log entries showing "Failed to read audio format" errors followed by abnormal termination
• Core dumps from FreeRDP processes indicating heap corruption or out-of-bounds access
• Anomalous RDP connections with malformed audio channel data

Detection Strategies

• Monitor FreeRDP server processes for unexpected termination or restart patterns
• Implement network-level inspection for malformed RDP audio input channel traffic
• Deploy application crash monitoring to detect heap corruption signatures in FreeRDP processes
• Use SentinelOne's behavioral AI to detect exploitation attempts targeting memory corruption vulnerabilities

Monitoring Recommendations

• Enable verbose logging on FreeRDP servers to capture audio format parsing errors
• Configure alerting for FreeRDP process crashes or abnormal memory usage patterns
• Monitor network traffic for unusual patterns in RDP audio input redirection channels
• Implement SentinelOne endpoint protection to detect and block memory corruption exploitation attempts

How to Mitigate CVE-2026-24682

Immediate Actions Required

• Upgrade FreeRDP to version 3.22.0 or later immediately
• If immediate patching is not possible, consider disabling audio input redirection on FreeRDP servers
• Review network access controls to limit exposure of FreeRDP servers to trusted networks
• Deploy SentinelOne endpoint protection to detect potential exploitation attempts

Patch Information

FreeRDP version 3.22.0 contains the official fix for this vulnerability. The patch corrects the error handling logic in audin_server_recv_formats to use a centralized cleanup routine with the correct iterator value. Organizations should upgrade to this version or later through their standard package management systems. The security fix is documented in the GitHub Security Advisory GHSA-vcw2-pqgw-mx6g.

Workarounds

• Disable audio input redirection on FreeRDP servers by removing the audin channel from the server configuration
• Implement network segmentation to restrict RDP server access to trusted clients only
• Deploy network-level filtering to inspect and block malformed RDP traffic
• Use application-level firewalls to limit RDP functionality to required features only

# Disable audio input redirection in FreeRDP server configuration
# Add to freerdp server command line or configuration:
--disable-audin

# Or remove audin from static channels if using channel configuration
# Ensure the audin channel is not loaded on server startup