| > who are seeking to run JS as part of the business logic You can, of course, safely use JS for business logic without executing code from unsafe sources, in the same way that you can safely use C#, LUA, Lisp, or any other language. But that aside, your criticism is completely irrelevant to the actual security flaw. I don't see any indication Avast was trying to use JS for business logic in the first place. I'm sure they over-embed crap for other parts of their interface, but that's not what's happening here. Avast was not loading a custom interpreter to execute their own business logic, they were loading a custom interpreter to analyze user files as part of their virus scan. > That service loads the low level antivirus engine, and analyzes untrusted data received from sources like the filesystem minifilter or intercepted network traffic. > Despite being highly privileged and processing untrusted input by design, it is unsandboxed and has poor mitigation coverage. It wasn't Avast's reliance on JS as a development tool that caused them to say, "maybe we should parse and run arbitrary files on the filesystem in a process with elevated permissions." It's their business logic that's the problem. Avast's business logic is, "we want to execute untrusted source code to see if it contains viruses." It wasn't a JS engineer saying, "I can't do my job in C++". It was a C/C++ engineer saying, "I know how I can tell if this file is dangerous -- I'll run it in the main process to see what it does." If you can tell me a safe way to accomplish that business logic in C/C++ or in any other language without process isolation or sandboxing, then I'll concede the point. But I'm pretty sure you can't. As an aside, an interesting followup to this disclosure would be if someone tested whether or not Avast is also interpreting other languages like LUA that they regard as potentially dangerous. I wouldn't necessarily take it as a given that JS was the only language they were doing this with. |