SVGO, short for SVG Optimizer, is a Node.js library and command-line application for optimizing SVG files. From version 2.1.0 to before version 2.8.1, from version 3.0.0 to before version 3.3.3, and before version 4.0.1, SVGO accepts XML with custom entities, without guards against entity expansion or recursion. This can result in a small XML file (811 bytes) stalling the application and even crashing the Node.js process with JavaScript heap out of memory. This issue has been patched in versions 2.8.1, 3.3.3, and 4.0.1.