Does anyone know of a comprehensive security guide about important basics / fundamentals which should be done to secure a web-server / website? A web link would do.
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To get started, you're probably going to want to focus on two things:
That's really two different specialties, and I don't think I'm going to be able to dig up a single document describing both... the ardent security nerd would also point out that this assumes you're working in a secure network with decent physical security, security policies and protections in other arenas.
Securing the Web Server
Hands down, you're best information is going to be web server specific - each one has it's own foibles. Sight unseen, I'd recommend this:
Yes, it's US DoD specific, but it's got some generally not so bad guidance.
I also really like NIST stuff:
Securing your website:
Hands down, my favorite site for secure web development is OWASP.
The information in this area is dense and there's a lot to take in no matter how you slice it. There's no one good checklist for web app security - you have to design security in from the start and be prepared to involve security considerations in all parts of development.
What I love about OWASP is their breakdown of specific issues, for example:
Gives you the problem, the threats, the vulnerabilities, examples, and some idea for what to do about it - pretty much everything I need, whether I'm the security analyst or the poor guy trying to fix the problem.
This is really a pretty stinking huge question. Based on your chosen tags it looks like you're asking for guidance on a LAMP stack, so we'll focus on that. There are already a number of related hardening questions posted, so for some additional insights check out these questions:
The specific techniques you take could depend highly on your environment and how your server will be used. Warning, this can take a lot of work in a test environment to build out and get done right. Followed by a lot of work to integrate into your production environment, and more importantly, business process.
First, however, check to see if your organization has any hardening policies, as those might be the most directly relevant. If not, depending on your role, this might be a great time to build them out. I would also recommend tackling each component separately from the bottom up.