CVE-2026-55192

A flaw was found in FreeRDP. A malicious Remote Desktop Protocol (RDP) server can provide a specially crafted H.264 video stream that causes the client's H.264 decoder to read beyond its allocated memory. This out-of-bounds read can lead to the disclosure of sensitive client memory or cause the client application to crash, resulting in a denial of service.

An out-of-bounds memory read flaw was found in FreeRDP's H.264 video decoder (libfreerdp/codec/h264.c). When handling AVC420 or AVC444 bitstreams, decoder backends fail to validate frame dimensions against negotiated RDPGFX surface boundaries. A malicious RDP server can send a video frame smaller than the surface, causing yuv420_context_decode and YUV-to-RGB conversion paths to read past allocated memory buffers. This allows an untrusted server to exfiltrate sensitive client memory contents or crash the client application.

The CVSS score(s) listed for this vulnerability do not reflect the associated product's status, and are included for informational purposes to better understand the severity of this vulnerability.

To mitigate this vulnerability, disable H.264 graphics acceleration in client connection parameters (e.g., omitting /gfx:avc420 or /gfx:avc444 in xfreerdp) to force legacy RemoteFX or standard software bitmap rendering.