Background Information Part:
We rent an IP Address Block and a DNS zone.
[We have to pay the annual fees, so they are renting, yes? ]
We don’t have enough information to know whether you’re renting or are the registrant, based on what you’ve said.
If you receive your domain name from a registrar, and the whois shows you to be the registrant, you’re the registrant. If you have a subdomain or you pay “rent” to someone who is shown as the registrant in the whois, then you’re just renting.
Likewise, if you receive your IP addresses from a regional Internet registry (ARIN in the NANOG region), you’re the LIR, or Local Internet Registry. If you have a subnet (which may be SWIPped into the whois, or may not) which you received from an LIR, then you’re just renting.
We run our own DNS authoritative server, with DNSsec on.
Meaning that you’re DNS signing both the forward (A/AAAA) and reverse (in-addr/ip6) zones?
Authority over DNS records, ROAs, and BGP table are with us, but authority over the Web Servers are (naturally) not.
It’s not clear what you mean by this. You mean that you don’t operate your own web servers, but instead use an outsourced service, which in turn uses its own IP addresses?
1. How (or where) can I monitor/control such that no one can ‘map’ my IP addresses to external FQDNs [hijacking my IPs] without me knowing about it?
These are separate and unrelated things.
Hijacking your IP addresses would be originating BGP announcement of them. Which other people should not do, and other people should not pay attention to if they’re validating ROAs and IRR entries.
Mapping your IP addresses to domain names (in-addr/ip6) is not an effective attack vector, and nobody will pay attention to anyway, if you’re the authoritative delegate for those blocks.
Mapping domain names to IP addresses (A/AAAA) is not an effective attack vector, and anyone can do, without disrupting anything.
1.1. My understanding is that, as long as I control the authoritative (DNSsec)server and people out there validate the DNS responses, hijacking my IPs outright for use somewhere else is (theoretically) impossible, yes?
If someone else conducts an effective DNS hijacking attack, intermediating themselves between your users and your servers, and your users don’t DNSSEC validate, then the attack will be successful. If your users do DNSSEC validate, AND THE APPS AND OSES THEY USE DON’T CIRCUMVENT IT, then the attack will fail. But that’s a big if. Many apps and OSes prefer a MITM attacker to a DNSSEC validation failure, because support costs.
2. But, web admins can still essentially ‘rent out’ part or whole of my websites by hosting 'forreign' pages/codes and allowing in ‘external redirection’ from outside (to use my hardware! my IPs!) anyway, yes?
If by “web admins” you mean third parties, rather than people who are responsible to you, yes. Which is why people concerned with security host their own services.
3. How (or where) can I monitor/control such that no one can ‘map’ FQDNs from within my DNS zone to external IP addresses [hijacking my hostnames] without me knowing about it?
There are at least three possibilities here.
One is that someone has access to the unsigned zone data below your delegation, in which case this is an internal security problem. If you’re using NSEC3 to prevent zone enumeration, and it were occurring in a delegated subdomain, this might actually be a difficult problem.
The second possibility is that someone external to your organization, who has access to DNS traffic flows (client, recursive, etc.) interposes themselves as a MITM or injects false data into a resolver cache. You could, hypothetically, buy access to “passive DNS” feeds which might reveal some portion of such traffic, if it existed, but that’s a very long shot.
A third (and probably most likely) possibility is that someone hijacks your domain at the registrar level, because registrars generally have crap security and fall over all the time, and registrants routinely use crap passwords to secure their accounts with registrars, etc. They could then add an additional nameserver, or substitute in all of their own nameservers. At that point, their actions would be fairly visible, and they’d still have to do a dirty roll of the DNSSEC KSKs, if they wanted to make things validate, but most wouldn’t bother doing so. There are monitoring services which watch for nameserver changes, but all the ones I’ve seen don’t actually check as often as they say they do, so miss attacks of this sort that are done quickly.
3.1. My understanding is that, web admins can write all sorts of ‘redirect’ in such a way that parts or even my whole websites can be ‘hosted’ on external IPs/hardware, yes?
Yep. See “why you shouldn’t do that” above.
4. Does that mean I need a big Web Application Firewall (WAF)
Absolutely not. I have no idea what a Web Application Firewall is, but if it’s anything like it sounds like, I wouldn’t let one anywhere near anything I was responsible for securing.
The thing is, no one should be able to use organization resources [IPs, FQDNs, and Web Services, for a start] for his/her own purpose without asking permission.
Sounds like you’re going to be writing a lot of shell scripts and cron jobs. Welcome to security. Remember to test your backups, that’s always the most important thing in any security regime.