FreeRDP’s H.264 decoder backends can allocate YUV planes sized solely from the bitstream, without comparing the decoded width and height to the RDPGFX surface dimensions used during region validation. When a malicious RDP server supplies an AVC420 or AVC444 stream whose decoded frame is smaller than the negotiated surface, the yuv420_context_decode and YUV‑to‑RGB conversion paths in libfreerdp/codec/h264.c read beyond the decoder‑owned planes, potentially leaking client memory or crashing the client. This out‑of‑bounds read is a classic buffer overread (CWE‑125) and was fixed in FreeRDP version 3.27.0.

The vulnerability affects all FreeRDP releases prior to version 3.27.0. Users running older FreeRDP binaries are exposed, while versions 3.27.0 and later include the fix.

The CVSS score of 7.2 indicates significant impact. No EPSS score is available and the vulnerability is not listed in the CISA KEV catalog, suggesting it has not been widely exploited yet. A malicious RDP server can supply an AVC420 or AVC444 stream whose decoded size is smaller than the negotiated surface, triggering the out-of-bounds read during the YUV‑to‑RGB conversion. Successful exploitation can leak memory contents or crash the client, impacting confidentiality, integrity, or availability of the end‑user system.