FreeRDP AVC444 Infinite Loop DoS via Malicious RDP Server

Executive Summary

This is a denial-of-service vulnerability in FreeRDP versions before 3.31.0. It occurs when decoding AVC444 metablocks with more region rectangles than the preallocated worker array size. A malicious RDP server can send crafted graphics updates causing the threaded decode path to loop indefinitely, consuming CPU resources and preventing normal client operation.

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Detection Guidance

This vulnerability can be detected by monitoring for abnormal CPU usage from FreeRDP processes or network traffic containing AVC444 graphics updates. Check for FreeRDP versions before 3.31.0 using package managers like 'apt list --installed | grep freerdp' or 'dnf list installed freerdp'. Inspect RDP server connections for repeated AVC444 metablock updates.

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Impact Analysis

This vulnerability can cause your FreeRDP client to become unresponsive or crash due to excessive CPU usage. It may disrupt remote desktop sessions, leading to loss of access to critical systems or services that rely on RDP connections.

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Mitigation Strategies

Immediately upgrade FreeRDP to version 3.31.0 or later. Block or restrict RDP connections from untrusted servers. Monitor network traffic for suspicious AVC444 graphics updates. If affected, terminate FreeRDP sessions and restart the client.

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