"Denial of service" is never a security bug; it's a huge mistake people have started classifying these things as such to start with. Serious bug? Sure. Loss of security? Not really.
That very much depends on what service is being denied. Nginx is _everywhere_. While not a direct security concern for nginx (instead an availablity issue) it could have security or safety implications for wider systems. What if knocking out nginx breaks a service for logging & monitoring security information? Or an ambulance call out management system? Or a payment progressing system for your business at the busiest time if your trading year? There are many other such examples. This sort of thing is why availablity can be considered a security matter and therefore why DoS vulnerabilities, particularly those affecting common software, are handled as security issues of significant severity.
Almost every bug can be considered a security bug under the wrong set of circumstances.
With fairly cheap ddos services you can "just" order you can knock most servers offline anyway. Internet reachability is rarely safety-critical, and if it is, that's probably a huge design flaw somewhere because there's tons of reasons outside of your control that can make the internet not work for either the server or clients.
Is all of this inconvenient and (potentially) a serious problem? Sure. But not "zomg criminals have credit card records / can spoof random domains / read private data / etc. etc." type serious.
> Almost every bug can be considered a security bug [...] With fairly cheap ddos services...
A DoS bug and an DDoS attack are very different things. One is a flaw that can bring a service down, the other is a brute force technique for making a service unusable. You can DDoS services without exploiting bugs.
I am aware; my point is that "denying the service" is pretty easy even without the presence of any bugs in the service. Stealing credit cards on the other hand...
We could argue that about almost anything though . There are always secondary effects possible and sometimes even likely. I can only think of the proverb/poem - "For want of a nail".
In those cases you just know that any problem can cause you trouble, so you pay attention to all problems including low severity ones like DoS, performance slowdowns or lack of bells and whistles.
Many security specialists via security as described by the CISSP material (Certified Information Systems Security Professional). Loosely speaking, that means ensuring the confidentiality, integrity, and availability of the system (including data received, data stored, and data sent).
Viewed in this light a bug that enables a successful Denial of Service (DoS) or Distributed Denial of Service (DDoS) attack is a security bug. A bug that causes a DoS or DDoS, but is not exploitable, would not be a security bug (e.g., some idiot added an infinite loop to the startup code). That's where issue triage comes in, a bug should never be assigned before its triaged. Sometimes triage results in 'we don't know enough' and someone gets assigned to evaluate the bug to answer specific questions before triage can finished. After triage is get assigned - or even better, a developer with a matching skill set chooses it to work on for the next release/sprint/etc.
Almost any bug in those kind of systems are potential security bugs. Not having the service available at all is probably among the least critical type of bug that can happen.
That very much depends on what service is being denied. Nginx is _everywhere_. While not a direct security concern for nginx (instead an availablity issue) it could have security or safety implications for wider systems. What if knocking out nginx breaks a service for logging & monitoring security information? Or an ambulance call out management system? Or a payment progressing system for your business at the busiest time if your trading year? There are many other such examples. This sort of thing is why availablity can be considered a security matter and therefore why DoS vulnerabilities, particularly those affecting common software, are handled as security issues of significant severity.