[danShumway]

> Contrast this with tailor-made, slim and well tested C++ code.

Avast is (was) running untrusted code in their system, by design. If your intention is to say that they shouldn't run untrusted code, then just say that. Don't waste time talking about whether memory safety matters for untrusted code -- just avoid untrusted code.

A lean C++ solution to the design problem of "how do we run untrusted code" is no better than an interpreted solution. You're focusing on the implementation, not the core design, and it is the core design that's flawed.

The only result of bringing JS up in a conversation like this is going to be to make people doing equally unsafe things in/with other languages feel better about themselves.

[LeoNatan25]

Again, what are you talking about?

No interpreter code should be running there, C, C++ or JS. What I am saying is that this design is made by or for people who are seeking to run JS as part of the business logic, which is ridiculous. I haven't brought up "memory safety" at all. Perhaps read the thread before commenting?

[danShumway]

> 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.

[mintplant]

> What I am saying is that this design is made by or for people who are seeking to run JS as part of the business logic

Nope, you've fundamentally misunderstood the issue at hand. The JS is not Avast's business logic. Rather, the program is attempting to analyze and detect malware in JS that the user encounters, similar to how an AV engine might inspect Microsoft Office files for malware. "Low-effort JS developers" had nothing to do with this. "C/C++ engineers" (and/or those above them) made this decision.

[catalogia]

> If your intention is to say that they shouldn't run untrusted code, then just say that.

Or maybe stop trying to "gotcha" other commenters by making assumptions about what they were trying to say.