Grav: Unauthenticated denial of service via unbounded image derivative dimensions

Grav is a file-based Web platform. Prior to 1.7.53 and 2.0.0-rc.8, Grav allows an unauthenticated visitor to exhaust server memory and CPU by requesting image derivatives with oversized dimensions through URL query image actions such as forceResize in Grav::fallbackUrl, which passes request parameters to ImageMedium magic actions without a dimension or pixel ceiling. This issue is fixed in versions 1.7.53 and 2.0.0-rc.8.