Uncontrolled Resource Allocation in FreeRDP

Executive Summary

CVE-2026-121388 is an uncontrolled resource allocation vulnerability in FreeRDP versions 3.0.0 through 3.32.1. A malicious RDP server can exploit the DRDYNVC DATA_FIRST PDU's 32-bit Length field to force clients to allocate up to 4,294,967,295 bytes of memory before validating the actual data size. This occurs because FreeRDP passes the declared length directly to StreamPool_Take without prior validation, leading to potential memory exhaustion and denial-of-service conditions.

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Detection Guidance

Monitor FreeRDP client processes for excessive memory usage during RDP connections. Check for connections to untrusted RDP servers with DRDYNVC enabled. Use network traffic analysis tools to inspect DATA_FIRST PDU Length fields in DRDYNVC channels for unusually large values.

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Impact Analysis

This vulnerability can impact you by causing your FreeRDP client to crash or become unresponsive due to memory exhaustion. If you connect to a malicious or compromised RDP server with DRDYNVC enabled, the server could force your system to allocate excessive memory, leading to performance degradation or a complete denial of service on your client machine.

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Mitigation Strategies

Upgrade FreeRDP to version 3.32.2 or later. Disable dynamic channels (DRDYNVC) if not required. Restrict RDP connections to trusted servers only. Implement network-level controls to block or monitor suspicious RDP traffic.

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