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Whitelisting Vs Blacklisting

August 24, 2011 4 comments

The fundamental principle that underpins all security is the need to stop bad people or processes while allowing good people or processes. So security is about access control; and  access control starts with identity. But identity on its own is not enough – we also need to understand purpose. We need to identify the person or process, and decide whether the intent is good or bad.

This article was written for, first published by, and reprinted here with the kind permission of
Infosecurity Magazine.

Consider passports in the physical world. They prove identity, but do not tell us intent: is the intent of that identity to do good or bad? We reinforce identity with lists of known intent: a whitelist of frequent flyers or VIPs whose intent is known to be good, and a blacklist of terrorists and bad people whose intent is known to be bad.

Cyber security is the same: based on identity and intent we maintain whitelists of known good (or at least acceptable) behavior, and blacklists of known bad (or unacceptable) behavior. Security is largely based on how we use these lists. In the main, we either allow what’s on the whitelist and prevent everything else; or we prevent what’s on the blacklist, and allow everything else. We tend to concentrate on one approach or the other: whitelisting or blacklisting.

Keeping our computers clean is a good example. In the beginning the anti-malware industry simply blacklisted the bad things. But now the alternative is gaining traction: whitelisting the good things. We need to know which is best for maximum security.

In favor of blacklisting

The basis of anti-virus security is a blacklist of all known malware. The technology is based on blacklisting because in the beginning there were very few viruses. A primary advantage of blacklisting is that it is conceptually simple to recognize a few bad things, stop them, and allow everything else.

A second argument in favor of blacklisting is ‘administrative ease’. The maintenance of blacklists is something we can delegate to trusted third parties – in this instance the anti-virus companies. They in turn, particularly with the advent of the internet, can automatically update the blacklist for us. Basically, we don’t have to do anything.

Daniel Power

Dan Power, UK regional manager, Spamina

Whitelisting is different: it is difficult to delegate to a third party the decision on which applications we need. “Whitelisting would be the perfect solution if people only have one computer that is never patched and never changed,” explains Dan Power, UK regional manager for anti-spam company Spamina. “Intellectually it makes perfect sense to only allow execution of the files that you know to be good.” But maintaining this whitelist is difficult. “The problem comes when you have to register or re-register every DLL every time you install a new, or patch an existing, application. Which people do you allow to install their own software, and which people do you stop? And which bits of software can make changes and which can’t? It becomes more of an administrative rather than intellectual issue.”

David Harley, senior research fellow at ESET LLC, agrees: “Whitelisting – which isn’t much different in principle to the integrity checking of yesteryear, requires more work by internal support teams and interferes with the end-users’ God-given right to install anything they like; which is more of a problem in some environments than in others.”

David Harley

David Harley, senior research fellow at ESET

That’s not to say that some people consider such delegation to be impossible. Last year Microsoft’s Scott Charney proposed a form of whitelisting for access to the internet; that is, only users with an internet health certificate for their computer should be allowed access. He has few supporters in the security industry. Power, again: “If computers were like televisions, with just one base operating system that was never changed, then it’s doable. But in the real world there are just so many variables associated with Windows and all the bits of software that have ever been written for Windows, that it’s almost impossible to be able to say what is and what is not a clean or healthy computer.”

Jennifer Gilburg

Jennifer Gilburg, director of marketing at Intel

Jennifer Gilburg, director of marketing at Intel, sees a different problem with this type of whitelisting. “Think of e-commerce,” she said. “An online trader would rather take the occasional fraudulent transaction than risk turning away a good transaction. So the thought of blocking a user from coming onto the internet until they are trusted would terrify many of the e-commerce providers who make their livelihood on the basis of the more users the better. I suspect that most of the e-commerce world would be lobbying very hard to put down this version of whitelisting.” So one of the strongest arguments in favor of blacklisting is the problems concerned with whitelisting.

In favor of whitelisting

Henry Harrison

Henry Harrison, technical director, Detica

However, Henry Harrison, technical director at Detica, points to a specific problem with blacklisting. “Anti-virus blacklisting,” he says, “is based on the idea of detecting things that are known to be bad and stopping them. But it simply cannot detect things that are bad, but not known.” Zero-day threats are not known simply because they are zero-day threats – and blacklisting merely lets them in as if they were good. “What we are seeing today,” continued Harrison, “is a lot of targeted, covert attacks – external infiltration into corporate networks with a view to the theft of valuable information using techniques that are specifically designed to evade blacklisting – and one possible response to zero-day threats is whitelisting.”

Lumension’s senior vice president Alan Bentley, points to the sheer volume of malware as a problem for blacklisting. “Blacklisting,” he explains, “is threat centric. Whitelisting is completely the opposite: it’s trust centric. While blacklisting malware used to be adequate, the whole threat arena in the cyberworld has exploded to such an extent we now have to question whether blacklisting alone is still good enough.”

Alan Bentley

Alan Bentley, senior vice president, Lumension

This is what Lumension does: it protects end-points (such as the PC on your desk) by making it administratively easy to create and maintain a whitelist of acceptable applications while supporting that with a blacklist of malware. “We believe that if you look at the two things together, whitelisting should absolutely be the first line of defense for any organization, because it simply stops everything that isn’t approved. But what it cannot do is remove malware once it has embedded itself into a machine.”

Bit9, like Lumension, is a company that concentrates on whitelisting. “The premise of application whitelisting is very simple,” explains Harry Sverdlove, chief technology officer. “What you want running on your system is a much smaller set than what you don’t want. We apply this model to other aspects of security in our life. For example, who do you let into your home? You don’t keep a list of everyone bad in the world. Rather, you only allow people into your home whom you trust.”

Harry Sverdlove

Harry Sverdlove, CTO, Bit9

What we’re seeing is that the explosion in malware (in excess of 2 million new pieces of malware every month) is exactly what makes us question whether blacklisting remains realistic. “As a general rule, whitelisting is always more secure than blacklisting,” continues Sverdlove. “But it requires you to think more about how software arrives on your systems and whether or not it is trustworthy. That’s why a software reputation database can be an invaluable aid in whitelisting – it provides a trust rating on software, like a trusted advisor or background security check service, that can make the process more manageable. If everything you run comes from a well-known third party, approving software almost exclusively from a cloud based reputation service can be enough. In most cases, however, you also have your only custom or proprietary software. An effective and robust whitelisting solution allows you to combine both your own policies along with those from a reputation database.”

So we should ask ourselves whether we can harness the power of cloud-based reputation systems to generate our whitelists. Spamina already uses this methodology to produce its blacklist of spam sources, calling on six separate reputation blacklists, but never relying on just one (thus minimizing the chance of false positives).

The anti-virus industry

“I’ve never advocated AV as a single defensive layer,” says ESET’s Harley. “Whitelisting can and does work for businesses, though it works best where there’s an authoritarian IT culture, rather than laissez-faire: restricted privileges and so on. I wouldn’t generally recommend it as a complete substitute for AV, but if it’s implemented properly, it’s a rational multi-layering strategy. It does, at a stroke, obviate most of the risk from social-engineering-dependent threats. In fact, most AV nowadays does have some whitelisting ability, though how it’s done and to what extent varies enormously.”

Ram Herkanaidu

Ram Herkanaidu, security researcher, Kaspersky Lab UK

Ram Herkanaidu, security researcher at Kaspersky Lab UK, has a similar viewpoint and acknowledges the increasing relevance of whitelisting. “As the amount of malware increases,” he said, “I can see at some point it could be more efficient to only allow whitelisted files to be run in an organization. The idea has been around for a while but many things have to be taken in consideration, like software updates (especially windows updates), remote users, smartphone and non-standard users.  Ideally as well as using the vendor’s whitelist you could have a local whitelist too.  So while the idea of having a, ‘trusted environment’ is very appealing, in practice it is difficult to achieve.”

Kaspersky, like other AV companies, is already looking into whitelisting. “We have been running a whitelist program to collect information about all known good files,” continued Herkanaidu. “The files are sent to us by our whitelist partners and also through our Kaspersky Security Network (KSN). This is our ‘neighborhood watch’ which users become part of when they install Kaspersky Internet Security. Information about all unknown files is sent to our ‘in the cloud’ service and automatically analyzed. If malicious, all computers within the network are protected. If it is not malicious it will be added to our whitelist.  This has two benefits for our customers: it will reduce the risk of false positives, and will increase scan speeds. In this way we have been able to collect information – not the files themselves – about millions of files.”

Whitelisting or blacklisting?

So what’s our conclusion? Whitelisting is fundamentally the better security solution. If something isn’t on the list, it gets stopped – the default position for whitelisting is secure.  But with blacklisting, if something isn’t on the list it gets allowed – the default position for blacklisting is insecure. Against this, the administrative effort involved in blacklisting is minimal compared to whitelisting; and the difference increases as the size of the whitelist increases. However, the efficiency of blacklisting decreases as its size increases. You could almost say that whitelisting is best with a small whitelist, while blacklisting is best with a small blacklist. However, since neither of these situations is likely to occur in the real world, our conclusion is simple: you need both.

Categories: All, Security Issues

Pulse 360 (highly) targeted pop-up adverts

August 23, 2011 4 comments

Now here’s a conundrum. I suddenly started seeing Pulse 360 adverts on my blog when using an old netbook running XP. Strange, I thought; I don’t know why they’re there. I checked on my OSX 10.6 running the very latest Firefox with NoScript. Nothing. I checked on other computers and other OS versions with older browsers. They showed on IE, Safari and Chrome. I asked my son, running Safari on OSX 10.5 with AdBlock. Nothing. He switched off AdBlock – and up they popped.

Uninvited Pulse 360 advert

Uninvited Pulse 360 advert

But it gets stranger. I asked security people what they thought. None of them could see any adverts – it only seems to be affecting me; or at least all of the computers behind my IP address.

But it’s multiple computers and multiple operating systems; so it’s not likely to be tied to a local infection. And after all, Pulse 360 is a legitimate business (yeah, right); so they wouldn’t do anything illegal. I suppose it could be something just affecting my router – that could affect internal browsers without affecting anything external. But it doesn’t seem likely.

So what are we left with? Has WordPress done a deal with Pulse 360? That doesn’t seem likely either (I’ve asked them, but haven’t had a reply yet).

What about the theme I use in WordPress? Could that have been compromised? But if so, why just pop them up on my computers and no-one else.

Or could the theme author have done a private deal with Pulse 360? By just showing the adverts to the blog owners, it could be an attempt to stay within the WordPress Terms and Conditions.

Frankly, I don’t know the answer. When I find out, I’ll let you know. Meantime, if the blog moves to Google blogs, you’ll know it was WordPress. If the theme suddenly changes, you’ll know it was the theme. But for the moment, it’s a conundrum – and I’m not happy.

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For the next chapter, see WordPress Pulse360 advertising: block them with NoScript and TACO with Abine on Firefox

Categories: All, Security Issues

David Starkey. Racist comments? Do me a favour

August 16, 2011 Leave a comment

If you have half a brain and any form of soul, you will inevitably have socialist leanings at heart. I take that to be a self-evident truth. And I own to it.

The problem is that socialism has been usurped by the absurd Labour Party, by politically-correct lefties who understand nothing about socialism and can only stand and repeat the politically-correct lefty mantras. One of those is that all middle-class, educated white men are inherently racist.

Take David Starkey. He made a valid point: whites have become black. In an historical context, black gangsta culture has been adopted by an element of white youth, and displayed itself in the multi-racial rioting we had last week.

How in God’s name is that a racist comment? But if you saw the incident (if not, it’s here) you will have seen the PC lefties determined to brand him a racist. They didn’t exactly shout him down but continually talked over him, not listening to him and either incapable of or simply refusing to understand him.

And now, Glorious Ed, joins the bandwagon. “It was an absolutely outrageous and disgusting comment – absolutely outrageous… they are racist comments…”

I suggest the leader of the absurd Labour Party should think again, and perhaps actually listen and respond to what Starkey really said.

Categories: All, Politics

Broken Britain? Disconnected, more like…

August 15, 2011 Leave a comment

Mr Cameron may bang on about ‘Broken Britain’ – and he ain’t wrong – but Jon Snow puts his finger on the real problem: Disconnected Britain. Until the people feel they have a real say in our country, until equal before the law is a fact not a hollow platitude, until the rich actually pay their tax levies in the same way as the poor, then last week will be just the beginning. Cameron doesn’t just have to mend Britain, he has to reconnect it as a single nation of equals.

Jon Snow: One law for the rich and another for the poor?

Categories: All, Politics

How very British

August 13, 2011 Leave a comment

After languishing in the doldrums of international cricket for decades, England is on the verge of taking the #1 position by thrashing the incumbents.

What do we feel? Joy? Elation?

No, a slight embarrassment over the act – and clear sympathy for the opposition.

Categories: All

Has Cameron joined the ‘increase security by cutting liberty’ mob?

August 11, 2011 Leave a comment

Chilling words from the Prime Minister today:

Mr Speaker, everyone watching these horrific actions will be stuck by how they were organised via social media.

Free flow of information can be used for good [eg, Egypt and the Arab Spring?]. But it can also be used for ill [eg, London?].

And when people are using social media for violence we need to stop them.

So we are working with the Police, the intelligence services and industry to look at whether it would be right to stop people communicating via these websites and services when we know they are plotting violence, disorder and criminality.

Despite the long history of Europe, it seems that we have yet to learn that killing the messenger doesn’t solve the problem.

Here’s a puzzle. How do you change ‘CAMERON’ to ‘BLAIR’?

Here’s a clue. It can only be done by reducing Cameron.

Categories: All, Politics, Security Issues

The weakest link is the user!

August 10, 2011 Leave a comment

As if we didn’t already know it, where security is concerned, the user is the flaw. Guido has published the perfect example:

Everyone has to carry around not only their government communications network issued Blackberry phone, but a Blackberry Smart Card Reader too, with another SIM card in it. If the two are separated by more than ten metres or so the Blackberry stops working. So if a pickpocket stole the Blackberry, it would stop working. Carrying two units is a little cumbersome and inconvenient. Unfortunately from a security point of view, the wonks and spinners have taken to just sello-taping the two of them back to back…
Downing Street’s iSpAd Blackberry Security Flaw

That’s our problem, folks.

Categories: All, Blogs, Security Issues

Anonymous and 5 November: hacktivism or hypocrisy?

August 10, 2011 Leave a comment

A quick addendum to my post on hacktivism (Where do you stand?).

The internet is abuzz with the apparent claim that Anonymous will take down Facebook on 5 November. I mentioned earlier that maybe we need to judge each individual act on its own merits. Here’s an example. While I applaud the attack on the Syrian MoD, I decry any attack on Facebook – and I cannot find any objective underlying principle for me to accept one and criticise the other (other than personal prejudice).

I do not like Facebook. I left it more than a year ago (see: Why I am leaving Facebook.). I think that Facebook should be abandoned (perhaps for Google+? we shall see).

But the idea that an anonymous group of Anonymous hackers should have the right to decide for me is simply absurd. It’s Anonymous behaving in the same way as those they decry: using force to impose their own wishes on others. If Anonymous goes ahead with this, whether they succeed or not, they should rename themselves from Anonymous to Hypocrites.

I say to the users, leave Facebook. I say to Anonymous, go and do something more fitting to your principles; don’t behave like those you oppose.

Anonymous hacks Syrian MoD – where do you stand on hacktivism?

August 8, 2011 Leave a comment

Anonymous has hacked the Syrian MoD website (as reported by Graham Cluley).

Graham Cluley's blog

...screenshot courtesy of Graham Cluley's blog

It once again highlights the moral dilemma inherent in hacktivism. The official non-Syrian view has to be that it is wrong. But if I was one of the unarmed civilian population of Syria being attacked and apparently indiscriminately shelled by more than 100 tanks, then I would consider it a worthy act.

The cop-out answer is to cite ‘rule of law – we live in a society where the law is supreme, and therefore if an act is against the law it is automatically wrong’.

I don’t accept this. Just because it is the law doesn’t make it right; and just because it is against the law doesn’t make it wrong. Morality is superior to legality; humanity demands that we do not accept evil laws, even if they are legally enacted. Ethnic cleansing, for example, is rarely illegal in the country enacting it.

So ask yourself this. If this hack had been performed by Syrian students with friends and families wantonly killed by Assad’s army, would it be hacking or heroism?

But then turn the coin round. If our own disenchanted youth hacked our own MoD site, would it be heroism or vandalism? There is no simple answer, and may be every one of us has to decide where we stand on each different occasion. In this instance I can only praise Anonymous and hope that none are ever caught or punished because of it. I may come to a different conclusion for a different act of hacktivism.

But one other thought occurs to me.

Presumably the hackers exploited a vulnerability on the site to be able to post up their own content – which means that someone with a financial rather than political intent could have planted malware on their site to infect visiting computers.
Graham Cluley, Syrian Ministry of Defense website hacked

If Anonymous can get in, then I’m certain that the NSA and Mossad and MI5 and the Second Office were all already in there. But will they be able to stay in there now that Anonymous has highlighted the weak security?

Categories: All, Politics, Security Issues
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