validGlxScreen(ClientPtr client, int screen, __GLXscreen **pGlxScreen, int *err)
{
     /*
     ** Check if screen exists.
     */
    if (screen >= screenInfo.numScreens) {
 	client->errorValue = screen;
 	*err = BadValue;
 	return FALSE;
    }
    *pGlxScreen = glxGetScreen(screenInfo.screens[screen]);

    return TRUE;
}

The product receives input or data, but it does not validate or incorrectly validates that the input has the properties that are required to process the data safely and correctly.