[TheDong]

I would argue that a stronger type system will generally reduce bugs, and some of those bugs will impact users (whether by corrupting their data, or breaking a feature, or even causing a security issue).

Most bugs are from the programmer having a misunderstanding about how the system works as they change it. The stronger the type system, the more potential misunderstandings can be verified statically by the compiler before they reach the user.

Other, dynamically typed languages, will require either having unit tests, or running it in prod to find that user who has a null email or whatever, and results in things going awry. Since we're talking about startups, there are of course no unit tests or users, so this is all largely academic. Like, if there are 0 users to trigger bugs, and a bug that could be statically detected by a good type system exists, does it make a sound?

[tptacek]

Stronger type systems do reduce bugs. But not all bugs are equal. When we talk about "velocity vs. safety" tradeoffs in SAAS software, we're virtually always talking about security vulnerabilities. There, it's much less clear that stronger type systems reduce vulnerabilities; in fact, the evidence mostly cuts the other way. As far as security is concerned, the major win is memory safety, and you can get that with plain 'ol Java or Python.

I'm bringing this up because in discussions like this, people tend to play fast and loose with the definitions of "safety". The kind of safety we're talking about in a decision between Rust and Java is mostly an externality to the SRE team, not to customers --- in other words, not an externality at all. An internality, if you will.

[TheDong]

Most vulnerabilities in boring web apps are not memory safety issues.

I've decided to pick an arbitrary list of security issues where the fixes will be visible to gain some small anecdotal evidence. The top result for "gitlab CVEs" is this august release announcement, let's look at the first three vulns on it: https://about.gitlab.com/releases/2022/08/30/critical-securi...

1. Remote Command Execution via GitHub import

This one was a typeing issue where an object with special keys resulted in dynamic code execution. That could not happen in rust. See the hn discussion here - https://news.ycombinator.com/item?id=33155527

2. Stored XSS via labels color

This can be made into a type-system issue with a good enough type system, text and html should be different types. Arguably this could happen with rust, but honestly, probably would not.

3. Content injection via Incidents Timeline description

This one is also arguably a typing issue for the same reason as above.

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Hey, look, 3 errors that type systems would help with and which had security implications.

> it's much less clear that stronger type systems reduce vulnerabilities; in fact, the evidence mostly cuts the other way.

What do you mean by that? In what case is a worse type-system (like java or go) going to make it harder to write vulnerabilities than a stronger type system (like haskell or rust)

[tptacek]

I'm simply going to say this again: Rust's type system doesn't meaningfully mitigate XSS, RCE, or metacharacter injection. You are equally likely to write an SQLI or an SSRF in Rust as you are in Java.

There are exactly two types of vulnerabilities Rust (and some other modern memory-safe languages) mitigate beyond memory corruption:

1. Java, Python, and Ruby have deserialization libraries that can easily be misused to create RCE vulnerabilities.

2. Python, Ruby, and Javascript have eval and eval-equivalents (which is essentially what your first example is).

You can pretend anything is a type system issue, but neither of these two vulnerabilities are properly understood as type safety errors. Java has a sharply more prescriptive and policed type system than Ruby does, but both have deserialization issues; it's just a generational thing.

Deserialization in new Java code is unlikely; deserialization is much less common than SSRF, which plagues Rust code just like everything else. In 2022, there is no meaningful security benefit to Rust over Java.

There are other reasons to use Rust! People should just stop making up fake security reasons to do it.