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HTTPS Interception Weakens TLS Security

us-cert.gov

81–90 of 105 posts

Re: HTTPS Interception Weakens TLS Security

#81
post #75
post #71

Earlier quoted context omitted.

We did think of that :) - we can detect your tampering with the forms we protect. But that said it doesn't stop everything if you can install a keylogger, or get the user to enter data somewhere else we can't stop it and it does depend on where in the user journey you try and protect things, as someone else here has pointed out if any of the journey is HTTP (or HTTPS being MITM) then they can send the user somewhere…

I am confused, initially you said "you can prevent MITM" now you say "doesnt stop everything...(HTTPS being MITM)". So your claim is that your product can or can not prevent MITM?

It can prevent MITM IF it's loaded in client page (defining MITM as network interception).

It can't stop keyloggers, people looking over your shoulder, malware in the browser (MITB)/plugins as it still sits within the browser sandbox. It can in some cases detect that, and in some cases hinder it.

An attacker can stop it loading by MITM the connection, but then the site can't work against it's APIs as the solution also verifies as data goes into those API's the encryption is present and the code isn't tampered. If it's tampered a business rule is applied to decide what to do, either stop the messages, OR pass it back to risk management systems (very common in finance).

Re: HTTPS Interception Weakens TLS Security

#82
post #67

Earlier quoted context omitted.

Don't forget RFC 2818 (HTTPS) which Chromium (and thus Chrome) recently broke mandatory features of: https://bugs.chromium.org/p/chromium/issues/detail?id=308330...

Is this a remake of that "embrace, extend, ..." movie of the 90s or this time it's cool?

It's really very similar. This is a case where the Chromium developers want to do something so they are going to do it, standards be dammed...

Re: HTTPS Interception Weakens TLS Security

#84

I still find it unfortunately shallow analysis. I'm currently fighting a battle in a company in the middle of rolling out Blue Coat ProxySG. I only became aware of it because it began causing interruptions to our work since none of the development tools get the necessary root cert to validate the certs that the proxy is rewriting. The root cert is only installed into the Windows credentials to make browsers work and…

This is exactly what my company went through just a few months ago when we hired an IT security guy whose first order of business was setting up a Palo Alto Networks firewall. Before turning on the MITM functionality he gave a presentation to everyone about what it did, and nobody (support staff, developers, administrators, management...nobody) seemed to mind except for me. This was what I sent to the HR lead immedia…

But it's far worse than that. Look further down in the thread where a security guy has pre-emptively invoked the "acceptable use" policy to cover for up for incompetence to secure the MITM proxy appropriately.

Acceptable use policies are not self-enforcing, they are really only used selectively, regardless if they say you shouldn't use your computer for personal use. Everybody does that to some degree and it is accepted in reality as long as it's within certain limits.

If the policy was self-enforcing then half the internet would be blocked, but of course companies don't do that because no one wants to work in that environment.

If you're watching porn or torrented movies, you'll either get a warning or fired, but the company will do nothing if you make an online payment.

But what happens if the proxy gets hacked and the attacker gets hold of your banking/personal logins/data? Who is most likely to discover the hack? Probably the same security guys who are managing the proxy. Will the security guys do the right thing and inform management that a hack occurred? Will the company also then do the right thing and inform all their employees that a hack occurred and now you might be missing some money? Will the company choose to hide behind the “acceptable use” policy to absolve itself from liability and say that it was you doing the wrong thing and stuck with the costs of your actions?

At each layer beginning at the individual working in the security team, to the whole security team, to the company management team, to everyone working at the company, that the incentives are aligned to cover up such an incident rather than reveal it.

The TLS inspection proxy is a bad system and worse still it’s a dangerous system in the hands of people who are not capable of providing and unbiased assessment of the risks they are exposing themselves and everyone else to, not to mention the company. It’s more than just financial risk, it’s the moral-hazard kinds of risk that really concern me because of the lack of transparency/understanding of its roll out, the incentives to cover up when something bad happens, and the lack of legal protections afterwards.

Re: HTTPS Interception Weakens TLS Security

#85
post #27

We need MITM detection in the browser. Yes, it's possible. The crypto bits the host is sending are different from the crypto bits the client is receiving. There are several ways to compare those, despite what the MITM box is doing. Out of band channels, timing, and order of data can be used. I sometimes refer to HTTPS Everywhere as "Security Theater Everywhere". Before the mania for HTTPS, many sites only used HTTPS…

Servers are better poised to detect it. Caddy can serve sites that warn browsers of HTTPS interception: https://github.com/mholt/caddy/pull/1430

Re: HTTPS Interception Weakens TLS Security

#86
post #32

Earlier quoted context omitted.

I don't think that's the correct interpretation of this document. A better title would be "Most TLS Proxies Considered Harmful", not TLS interception as a whole. US-CERT is explicitly calling out that many appliances and applications often are weakening security vs. the common TLS clients, by way of not properly validating certificate chains by proxy for the client and otherwise masking SSL/TLS issues from being surf…

> I don't think that's the correct interpretation of this document. A better title would be "Most TLS Proxies Considered Harmful", not TLS interception as a whole. This is the usual reaction to this I see everywhere. It doesn't match with reality. Read the complete paper by Halderman et al [1]. It says pretty clearly that all existing products lower the security in one way or another: "Our grading scale focuses on th…

Is better TLS interception actually possible? Is it just that it's usually badly implemented, or is it a fundamental weakening?

Other than the unavoidable weakening of having another system seeing the unencrypted data, which is inherent in using one of these systems and can never go away.

Re: HTTPS Interception Weakens TLS Security

#87
post #45

Earlier quoted context omitted.

I strongly disagree: who is in control, how it is implemented, and the purpose of the product are all both extremely important and fundamentally different between the two use cases. An "antivirus" filter ends up implemented as a man-in-the-middle attack between software I wrote and servers I contract and control, wherein protections that were actively put in place are stripped away in order to increase the attack sur…

> If you really believe in true end-to-end encryption, then having this webserver in the middle is a bad idea: you should route requests directly to database servers and ensure that at no point does any non-database computer have a decrypted copy of the information that will eventually be rendered to the user. I can't say I haven't considered abusing PL/pgSQL to that point... ;)

I've actually seen that done - HTML straight out of a stored procedure. Really awesome stuff.

I've mostly recovered from the experience, thanks, although I do have occasional flashbacks.

Re: HTTPS Interception Weakens TLS Security

#88
post #86
post #32

Earlier quoted context omitted.

> I don't think that's the correct interpretation of this document. A better title would be "Most TLS Proxies Considered Harmful", not TLS interception as a whole. This is the usual reaction to this I see everywhere. It doesn't match with reality. Read the complete paper by Halderman et al [1]. It says pretty clearly that all existing products lower the security in one way or another: "Our grading scale focuses on th…

Is better TLS interception actually possible? Is it just that it's usually badly implemented, or is it a fundamental weakening? Other than the unavoidable weakening of having another system seeing the unencrypted data, which is inherent in using one of these systems and can never go away.

> Is better TLS interception actually possible? Is it just that it's usually badly implemented, or is it a fundamental weakening?

In theory, yes, apart from the obvious "more attack surface" problem. They could check for HPKP, CRLset, CT. They could even do more. (CT checking is very basic in Chrome and nonexistent in other browsers.)

However in reality? No. In the real world Bluecoat manages to break TLS 1.3 deployment, although its designers tried everything to avoid that and they have been asked by Google to test that.

Re: HTTPS Interception Weakens TLS Security

#89
post #45
post #13

Earlier quoted context omitted.

There is limited distinction there. Both terminate and re-establish TLS sessions.

I strongly disagree: who is in control, how it is implemented, and the purpose of the product are all both extremely important and fundamentally different between the two use cases. An "antivirus" filter ends up implemented as a man-in-the-middle attack between software I wrote and servers I contract and control, wherein protections that were actively put in place are stripped away in order to increase the attack sur…

>An "antivirus" filter ends up implemented as a man-in-the-middle attack between software I wrote and servers I contract and control, wherein protections that were actively put in place are stripped away in order to increase the attack surface. A reverse proxy is something that I actively implemented as part of my infrastructure, and I am contracting for it and paying for it like anything else I rent.

Those can equally happen the other way around. You might put an antivirus filter in place on your own network. Your hosting provider might set up their own reverse proxy.

> But like, think about it this way: Apache is also an SSL termination point. The code in your website is likely 99% "transform a URL into SQL, then transform the result into HTML": it is just a dumb encoder/decoder, and pretty exactly analogous to an SSL termination point. If you really believe in true end-to-end encryption, then having this webserver in the middle is a bad idea: you should route requests directly to database servers and ensure that at no point does any non-database computer have a decrypted copy of the information that will eventually be rendered to the user.

I agree with that - best to have the database and the web server on the same server, communicating via local socket or shared memory. Better still to compile the web layer and the data layer into the same unikernel. Current best practice (e.g. PCI-DSS) seems to accept having an (encrypted) network connection between distinct web and database servers, but only within a single physically secured rack. You're right that if you do the same thing with a load balancer (have it in the same physically secured rack as your web servers, encrypt connections between it and them) then it's no less secure, but I don't think people would want to be using a load balancer within a single rack anyway, since most of the point of a load balancer is availability and you want separate racks for that. Certainly a third-party reverse-proxy is a substantial weakening of security.

> I don't see many people (though if you are, that's great, and then I'd be really happy ;P) insisting that everyone build their own computers and host them at their office, to make sure decrypted data never touches a computer owned and operated by someone else.

I wouldn't go that far - AIUI PCI-DSS etc. require you have physically secured/access-controlled servers but allow you to rent space/power/cooling from a datacenter operator (though they don't get access to your rack, and possibly have to also be audited themselves).

> Let's say that CDNetworks is failing to check SSL certificates correctly: how exactly are you going to attack that against my website? I mean, sure: if you are a state-level actor, that is going to be easy, but otherwise, that's going to be extremely rough. An "antivirus" filter that, as described in this alert, is failing to correctly check SSL certificates... well, that opens you up to attack by amateur attackers that are "close to you", such as a stalker or an ex-spouse or a corporate competitor.

It's a different risk profile to be sure. Are you more worried about someone making a large-scale attack against the remote service you were connecting to, or just against the Internet in general? Or someone making a small-scale local attack? I think both can be serious; it's not just state-level actors but also large criminal rings or even political groups that would potentially have the resources to execute an attack against a particular service (e.g. a medical provider doing something politically contentious, or just anything that accepts credit cards / personal information).

Re: HTTPS Interception Weakens TLS Security

#90

I still find it unfortunately shallow analysis. I'm currently fighting a battle in a company in the middle of rolling out Blue Coat ProxySG. I only became aware of it because it began causing interruptions to our work since none of the development tools get the necessary root cert to validate the certs that the proxy is rewriting. The root cert is only installed into the Windows credentials to make browsers work and…

  > The answer is that you more than likely have no protection at 
  > all (likely not even in workplace law). Even if you suspected 
  > someone had inappropriately accessed your personal details, 
  > the company almost certainly has an IT policy saying that you 
  > shouldn't be using your computer for personal use.
The answer is to stop ignoring the policy. Reserve the corporate device for work activities. Use personal devices for personal things and consider the corporate network to be hostile -- use a VPN.
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