Safety and Protection Against DoS Attacks ======================================== {{#include ../links.md}} For scripting systems open to untrusted user-land scripts, it is always best to limit the amount of resources used by a script so that it does not consume more resources that it is allowed to. The most important resources to watch out for are: * **Memory**: A malicious script may continuously grow a [string], an [array] or [object map] until all memory is consumed. It may also create a large [array] or [object map] literal that exhausts all memory during parsing. * **CPU**: A malicious script may run an infinite tight loop that consumes all CPU cycles. * **Time**: A malicious script may run indefinitely, thereby blocking the calling system which is waiting for a result. * **Stack**: A malicious script may attempt an infinite recursive call that exhausts the call stack. Alternatively, it may create a degenerated deep expression with so many levels that the parser exhausts the call stack when parsing the expression; or even deeply-nested statement blocks, if nested deep enough. Another way to cause a stack overflow is to load a [self-referencing module][`import`]. * **Overflows**: A malicious script may deliberately cause numeric over-flows and/or under-flows, divide by zero, and/or create bad floating-point representations, in order to crash the system. * **Files**: A malicious script may continuously [`import`] an external module within an infinite loop, thereby putting heavy load on the file-system (or even the network if the file is not local). Even when modules are not created from files, they still typically consume a lot of resources to load. * **Data**: A malicious script may attempt to read from and/or write to data that it does not own. If this happens, it is a severe security breach and may put the entire system at risk.