If I get a dependabot alarm for my Rails project, I would do well to make a bet that it's a nokogiri vulnerability. I haven't looked into the "why" or what's really going on, but it does feel like there's a lot of room to look at attack surface or any core design issues.
Nokogiri is one of the most security-sensitive parts of any Rails codebase, since it's used for parsing and sanitizing untrusted HTML and XML documents. Accordingly, there's a lot of scrutiny on it (and its upstream dependency, libxml2). That said, as far as I'm aware, almost all of the recent vulnerabilities I've noticed have been related to XSLT and other obscure XML features that most people probably don't use (and aren't enabled by default). So there's a combination of both 1) lots of scrutiny on the library itself leads to high security standards and 2) the goal of fully-featured XML processing adds a large attack surface that may not be relevant to most people that leads to a lot of vulnerability alerts.
Personally though, I've been seeing almost 10x the amount of alerts for useless "vulnerabilities" like ReDOS in nodejs projects though. Either way, alert fatigue is real.
XML is chock-full of misfeatures ripe for creating security vulnerabilities. It's not just nokogiri – XML parsing libs are one of the hottest sources of vulnerability notifications in many ecosystems (a large number of those CVE alerts come by way of using libxml2 under the hood, which nokogiri also depends on).
Safely parsing untrusted XML is an extremely hairy task.
