CVE-2026-24677: FreeRDP Use-After-Free Vulnerability

CVE-2026-24677 Overview

CVE-2026-24677 is a high-severity out-of-bounds read vulnerability affecting FreeRDP, the widely-used open-source implementation of the Remote Desktop Protocol (RDP). The vulnerability exists in the ecam_encoder_compress_h264 function, which improperly trusts server-controlled dimensions without validating the source buffer size, resulting in an out-of-bounds read condition when calling sws_scale. This flaw allows a malicious RDP server to trigger memory access violations in connected clients, potentially leading to denial of service or information disclosure.

Critical Impact

Remote attackers operating a malicious RDP server can exploit this vulnerability to cause denial of service conditions in FreeRDP clients by triggering out-of-bounds memory reads through manipulated dimension parameters.

Affected Products

• FreeRDP versions prior to 3.22.0
• FreeRDP rdpecam channel implementations using H.264 encoding
• Systems utilizing FreeRDP client libraries for Remote Desktop connections

Discovery Timeline

• 2026-02-09 - CVE CVE-2026-24677 published to NVD
• 2026-02-10 - Last updated in NVD database

Technical Details for CVE-2026-24677

Vulnerability Analysis

This vulnerability represents an out-of-bounds read condition in FreeRDP's camera redirection channel (rdpecam). The core issue lies in the ecam_encoder_compress_h264 function's handling of video stream dimensions. When processing H.264 encoded camera data, the function accepts dimension parameters that are controlled by the remote server without performing adequate validation against the actual source buffer size.

The vulnerable code path involves the sws_scale function from the FFmpeg/libswscale library, which performs image scaling and format conversion. When the server provides malicious dimensions that exceed the actual buffer boundaries, sws_scale attempts to read beyond allocated memory regions, resulting in an out-of-bounds read condition.

Root Cause

The root cause of CVE-2026-24677 is improper input validation in the CameraDeviceStream structure handling. The vulnerability stems from a missing size validation check that should ensure the sws (software scaling) context dimensions match the actual source buffer dimensions. The patch introduces swsWidth and swsHeight tracking variables to the CameraDeviceStream structure, enabling proper validation before scaling operations occur.

Attack Vector

The attack vector is network-based, requiring no authentication or user interaction beyond establishing an RDP connection to a malicious server. An attacker could set up a rogue RDP server configured to send crafted camera redirection responses with manipulated dimension parameters. When a victim's FreeRDP client connects and enables camera redirection functionality, the malicious server can trigger the out-of-bounds read by specifying dimensions that exceed the client's buffer boundaries.

// Security patch in channels/rdpecam/client/camera.h
// Source: https://github.com/FreeRDP/FreeRDP/commit/d2d4f449312ddafd4a4c6c8a4f856c7f0d44a3b5

 #endif
 
 	/* sws_scale */
+	uint32_t swsWidth;
+	uint32_t swsHeight;
 	struct SwsContext* sws;
 
 } CameraDeviceStream;

The fix adds explicit tracking of the sws context dimensions (swsWidth and swsHeight) to the CameraDeviceStream structure, allowing the code to validate that scaling operations do not exceed the allocated buffer size.

Detection Methods for CVE-2026-24677

Indicators of Compromise

• Unexpected FreeRDP client crashes or segmentation faults during RDP sessions
• Memory access violation errors in system logs related to FreeRDP processes
• Abnormal RDP traffic patterns with unusually large or malformed camera redirection packets
• Core dumps containing evidence of out-of-bounds memory access in sws_scale or ecam_encoder_compress_h264 functions

Detection Strategies

• Monitor for FreeRDP client process crashes, particularly those with memory access violations in the rdpecam channel code paths
• Implement network intrusion detection rules to identify anomalous RDP camera redirection traffic with suspicious dimension parameters
• Deploy endpoint detection and response (EDR) solutions capable of monitoring memory access patterns in FreeRDP processes
• Audit FreeRDP version deployments across the environment to identify systems running vulnerable versions prior to 3.22.0

Monitoring Recommendations

• Enable verbose logging for FreeRDP client connections to capture detailed error information
• Configure crash reporting mechanisms to automatically collect and analyze FreeRDP client failures
• Establish baseline metrics for normal RDP session behavior to help identify anomalous connection patterns
• Implement network flow analysis to detect connections to unknown or suspicious RDP servers

How to Mitigate CVE-2026-24677

Immediate Actions Required

• Upgrade FreeRDP to version 3.22.0 or later immediately across all affected systems
• Temporarily disable camera redirection functionality in FreeRDP client configurations if patching is not immediately possible
• Review and restrict RDP connections to trusted, known servers to minimize exposure to malicious server attacks
• Implement network segmentation to limit which systems can establish outbound RDP connections

Patch Information

The vulnerability has been addressed in FreeRDP version 3.22.0. The fix introduces proper dimension tracking in the CameraDeviceStream structure by adding swsWidth and swsHeight fields to validate that the sws scaling context matches the actual buffer dimensions before processing. Organizations should apply this patch by upgrading to the latest FreeRDP release. The security patch is available through the FreeRDP GitHub commit. Additional details are available in the GitHub Security Advisory.

Workarounds

• Disable the rdpecam (camera redirection) channel by removing it from the enabled channels list in FreeRDP configuration
• Use firewall rules to restrict outbound RDP connections to pre-approved server addresses only
• Deploy application-level whitelisting to control which RDP servers users can connect to
• Consider using alternative RDP client implementations until patching can be completed

# Configuration example - Disable camera redirection in FreeRDP
# Add to FreeRDP client command line or configuration
xfreerdp /v:server.example.com /u:username -rdpecam

# Or explicitly disable the channel
xfreerdp /v:server.example.com /u:username /vc:-rdpecam