Scangate Re-visited: Vulnerability Scanners Uncovered

I have covered VA tools before but I feel that one year later, the same misconceptions prevail. The notion that VA tools really can be used to give a decent picture of vulnerability is still heavily embedded, and that notion in itself presents a serious vulnerability for businesses.

A more concise approach at a run down on the functionality of VA warez may be worth a try. At least lets give it one last shot. On second thoughts, no, don’t shoot anything.

Actually forget “positive” or “negative” views on VAs before reading this. I am just going to present the facts based on what I know myself and of course I’m open to logical, objective discussion. I may have missed something.

Why the focus on VA? Well, the tools are still so commonplace and heavily used and I don’t believe that’s in our best interests.

What I discovered many years ago (it was actually 2002 at first) was that discussions around these tools can evoke some quite emotional responses. “Emotional” you quiz? Yes. I mean when you think about it, whole empires have been built using these tools. The tools are so widespread in security and used as the basis of corporate VM programs. VM market revenues runs at around 1 billion USD annually. Songs and poems have been written about VAs – OK I can’t back that up, but careers have been built and whole enterprise level security software suites built using a nasty open source VA engine.

I presented on the subject of automation in VA all those years ago, and put forward a notion that running VA tools doesn’t carry much more value as compared to something like this: nmap -v -sS -sV <targets> . Any Security Analyst worth their weight in spam would see open ports and service banners, and quickly deduce vulnerability from this limited perspective. “Limited”, maybe, but is a typical VA tool in a better position to interrogate a target autotragically?

One pre-qualifier I need to throw out is that the type of scanners I will discuss here are Nessus-like scanners, the modus operandi of which is to use unauthenticated means to scan a target. Nessus itself isn’t the main focus but it’s the tool that’s most well known and widely used. The others do not present any major advantages over Nessus. In fact Nessus is really as good as it gets. There’s a highly limited potential with these tools and Nessus reaches that limit.

Over the course of my infosec career I have had the privilege to be in a position where I have been coerced into using VAs extensively, and spent many long hours investigating false positives. In many cases I set up a dummy Linux target and used a packet sniffer to deduce what the tool was doing. As a summary, the findings were approximately:

  • Out of the 1000s of tests, or “patterns”, configured in the tools, only a few have the potential to result in accurate/useful findings. Some examples of these are SNMP community string tests, and tests for plain text services (e.g. telnet, FTP).
  • The vast majority of the other tests merely grab a service “banner”. For example, the tool port scans, finds an open port 80 TCP, then runs a test to grab a service banner (e.g. Apache 2.2.22, mickey mouse plug-in, bla bla). I was sort of expecting the tool to do some more probing having found a specific service and version, but in most cases it does not.
  • The tool, having found what it thinks is a certain application layer service and version, then correlates its finding with its database of public disclosed vulnerabilities for the detected service.

Even for some of the plan text services, some of the tests which have the potential to reveal useful findings have been botched by the developers. For example, tests for anonymous FTP only work with a very specific flavour of FTP. Other FTP daemons return different messages for successful anonymous logins and the tool does not accommodate this.

Also what happens if a service is moved from its default port? I had some spectacular failures with running Nessus against a FTP service on port 1980 TCP (usually it is listening on port 21). Different timing options were tested. Nessus uses a nmap engine for port scanning, but nmap by itself is usually able to find non-default port services using default settings.

So in summary, what the VA tools do is mostly just report that you are running ridiculous unencrypted blast-from-the-past services or old, down-level services – maybe. Really I would hope security teams wouldn’t need to spend 25K USD on an enterprise solution to tell them this.

False positives is one thing, but false negatives is quite another. Popular magazines always report something like 50% success rate in finding vulnerabilities in staged tests. Why is it always 50%? Remember also that the product under testing is usually one from a vendor who pays for a full spread ad in that magazine.

Putting numbers to false negatives makes little sense with huge, complex software packages of millions of lines of source code. However, it occurred to me not so long ago whilst doing some white box testing on a client’s critical infrastructure: how many of the vulnerabilities under testing could possibly be discovered by use of a VA tool? In the case of Oracle Database the answer was less than 5%. And when we’re talking Oracle, we’re usually talking critical, as in crown jewels critical.

If nothing else, the main aspect I would hope the reader would take out of this discussion is about expectation. The expectation that is set by marketing people with VA tools is that the tools really can be used to accurately detect a wide range of vulnerability, and you can bet your business on the tools by using them to test critical infrastructure. Ladies and gentlemen: please don’t be deceived by this!

Can you safely replace manual testing with use of these tools? Yes, but only if the target has zero value to the business.

 

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2 thoughts on “Scangate Re-visited: Vulnerability Scanners Uncovered

  1. How would you rate purely commercial offerings like Qualys. The have really good authenticated scan features. I have used it couple of times and found good results. Neither did I perform extensive research on the results to test false positives and negatives, nor I have used it extensively to confirm my remarks. Like to know your thoughts.

    • Sure, well I think Qualys is as good as it gets in terms of authenticated VA – although I have not yet seen Tripwire’s Policy Manager. I think overall, across the whole market, the emphasis is still very much on unauthenticated, “blind” scans with not so much attention being put into authenticated methods.
      With regard false positives and authenticated scans, the potential is there for zero false positives because with admin rights, the scanner can literally “see” everything. However, there are still some false positives. As an example: user accounts with weak passwords are flagged but the scanner didn’t check that the accounts are locked/expired.
      Qualysguard does dump a lot of config data, so that’s good. It is better in some areas than others. They use RAT for Cisco IOS testing – and RAT is excellent. Other areas such as Unix flavours and databases are not so good but better than nothing. The worse thing though (and this is bad): all your config data and passwords will be hosted by Qualys! The scanner is PHP and runs over a public URL, so your configs are all hosted by Qualys.
      Hope that helps.

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