CVE-2026-26955: FreeRDP has Out-of-bounds Write

FreeRDP is a free implementation of the Remote Desktop Protocol. Prior to version 3.23.0, a malicious RDP server can trigger a heap buffer overflow in FreeRDP clients using the GDI surface pipeline (e.g., xfreerdp) by sending an RDPGFX ClearCodec surface command with an out-of-bounds destination rectangle. The gdiSurfaceCommandClearCodec() handler does not call iswithinsurface() to validate the command rectangle against the destination surface dimensions, allowing attacker-controlled cmd->left/cmd->top (and subcodec rectangle offsets) to reach image copy routines that write into surface->data without bounds enforcement. The OOB write corrupts an adjacent gdiGfxSurface struct's codecs pointer with attacker-controlled pixel data, and corruption of codecs is sufficient to reach an indirect function pointer call (NSCCONTEXT.decode at nsc.c:500) on a subsequent codec command — full instruction pointer (RIP) control demonstrated in exploitability harness. Users should upgrade to version 3.23.0 to receive a patch.