Hacker News Board Hacker News, browsed like a classic message board
Live data from Hacker News

Let’s Encrypt Now Being Abused by Malvertisers

blog.trendmicro.com

Post reply on HN
Print view View original

51–60 of 71 posts

Re: Let’s Encrypt Now Being Abused by Malvertisers

#51

Post by tremon »

pfg wrote: post #44
nippoo wrote: post #41

Earlier quoted context omitted.

Or perhaps do it the other way around? Make a Let's Encrypt subdomain-blacklisting TXT record with which the parent domain could indicate that they don't want subdomain owners to be able to create their own SSL certificates. (Useful in the case of hosted web services, for example, where the parent already owns a wildcard certificate so there's no reason for the subdomain to create one)

This is already possible using CAA DNS records, which can be used to define which CAs should be permitted to issue certificates for a domain.

That's great. But according to https://tools.ietf.org/html/rfc6844, this is quite recent, and not standardized yet.

Do you have any information on which CA's already support this, or whether Let's Encrypt (intends to) support this?

I'm still hoping for DANE to gain traction, though. Not necessarily as a replacement for CA's; there is value in thorough, third-party validation of certificates, but not within the current ecosystem.

Re: Let’s Encrypt Now Being Abused by Malvertisers

#52

Post by pfg »

tremon wrote: post #51
pfg wrote: post #44

Earlier quoted context omitted.

This is already possible using CAA DNS records, which can be used to define which CAs should be permitted to issue certificates for a domain.

That's great. But according to https://tools.ietf.org/html/rfc6844 , this is quite recent, and not standardized yet. Do you have any information on which CA's already support this, or whether Let's Encrypt (intends to) support this? I'm still hoping for DANE to gain traction, though. Not necessarily as a replacement for CA's; there is value in thorough, third-party validation of certificates, but not within the curre…

Yes, Let's Encrypt does support CAA. Not sure about other CAs.

Re: Let’s Encrypt Now Being Abused by Malvertisers

#53

Post by pfg »

supermatt wrote: post #50
pfg wrote: post #42

Earlier quoted context omitted.

WoSign is one of the other CAs offering this option. It is unclear to me how TXT verification would have prevent this. The article indicates that the attackers created the subdomain and pointed it at a server they controlled; this means DNS was compromised and creating a TXT record wouldn't have been a problem. Domain owners which are worried about Let's Encrypt can opt to create a CAA DNS record that limits CAs allo…

I simply see it as an additional (and unnecessary) attack vector. If you are unable to hijack the DNS servers or poison/spoof the cache used by the CA, then you have the luxury of a whole new (and often WAY more insecure) attack surface. Then you have a cert for that domain which can be used for other, more targeted purposes. EDIT: IGNORE BELOW, I WAS ASSUMING THAT LETS ENCRYPT LETS YOU VALIDATE SUBDOMAINS FROM THE T…

No, with Let's Encrypt you would have to have full control over contents of login.wifiprovider.com to get a certificate for that domain. Specifically, you'd have to be able to serve a token at

    http://login.wifiprovider.com/.well-known/acme-challenge/random
Verifying ownership of wifiprovider.com that way would not automatically allow you to get certificates for subdomains too.

Re: Let’s Encrypt Now Being Abused by Malvertisers

#54

Post by supermatt »

pfg wrote: post #53
supermatt wrote: post #50

Earlier quoted context omitted.

I simply see it as an additional (and unnecessary) attack vector. If you are unable to hijack the DNS servers or poison/spoof the cache used by the CA, then you have the luxury of a whole new (and often WAY more insecure) attack surface. Then you have a cert for that domain which can be used for other, more targeted purposes. EDIT: IGNORE BELOW, I WAS ASSUMING THAT LETS ENCRYPT LETS YOU VALIDATE SUBDOMAINS FROM THE T…

No, with Let's Encrypt you would have to have full control over contents of login.wifiprovider.com to get a certificate for that domain. Specifically, you'd have to be able to serve a token at http://login.wifiprovider.com/.well-known/acme-challenge/random Verifying ownership of wifiprovider.com that way would not automatically allow you to get certificates for subdomains too.

Thanks. I was assuming it would work the same as other CAs in that respect.

I'm still not sure about this mechanism of verification, but good to know that my example scenario cant exist.

Re: Let’s Encrypt Now Being Abused by Malvertisers

#55

Post by userbinator »

MrSwagga wrote: post #24
ars wrote: post #13

I'm unclear about what the problem is. So the traffic is encrypted. How does that make anything worse? It seems pretty irrelevant to me if it's encrypted or not.

Maybe because it can't be automatically detected by some layer 7 firewall filters/web proxies.

Although some seem a bit squeamish about it, any good firewall/filtering solution should do SSL MITM --- especially now that encrypted connections are becoming the norm.

Given that Trend Micro themselves provide AV software that does this, it's particularly ironic since it's already no problem for them to decrypt and scan encrypted traffic. It's likely just their CA division that dislikes Let's Encrypt.

Re: Let’s Encrypt Now Being Abused by Malvertisers

#56

Post by jmuguy »

pdkl95 wrote: post #32

> gained the ability to create subdomains under a legitimate domain As lots of people in this thread have already pointed out, that's the security problem. The DNS zone that was delegated to you, then you have a responsibility to keep the "squatters" away. > Traffic to this created subdomain was protected with HTTPS Good. HTTP is obsolete. That doesn't change anything from the perspective of the victim. > an open Dou…

As evidenced by the comments here, the people that count, that is system admins and developers, don't see a problem. Just more FUD from the traditional security players trying to remain relevant.

Re: Let’s Encrypt Now Being Abused by Malvertisers

#57

Post by Sujan »

pdkl95 wrote: post #32

> gained the ability to create subdomains under a legitimate domain As lots of people in this thread have already pointed out, that's the security problem. The DNS zone that was delegated to you, then you have a responsibility to keep the "squatters" away. > Traffic to this created subdomain was protected with HTTPS Good. HTTP is obsolete. That doesn't change anything from the perspective of the victim. > an open Dou…

> > These DV certificates can help the hacker gain legitimacy with the public.

> How?

By the lock displayed in the browser that couldn't be there for free that easy before.

Re: Let’s Encrypt Now Being Abused by Malvertisers

#58

Post by tremon »

rmhrisk wrote: post #9

My post responding to this - https://unmitigatedrisk.com/?p=552

Thanks for that response. It is well-written and transparently constructed. That said, you're reading quite a bit more agenda and polemic in TrendMicro's post than I did. Possibly because you've seen this kind of post before :)

If you can allow me a bit of proofreading, there are a few typo's in the article:

[..] that said it is can be summarized as: -> lose the "is"

Maybe the then the issue is -> lose the first "the"

It had nothing to do with SSL, the attacker had full control of a subdomain and the attack would have still worked without it. -> The final "it" should presumably refer to SSL, but in this construct it refers to "control".

I say “could” because in that not everyone is aware of -> lose "in that" ?

Until all CAs are required to log all of the SSL certificates they issue into CT Logs and add are required to CAA -> Not sure of your intent here. "And CAA records are required before requesting certs"?

Also, your quotes from the original article render for me (in firefox) as single-line textboxes with scrollbars. Maybe you can change it to force automatic wrapping?

Re: Let’s Encrypt Now Being Abused by Malvertisers

#59

Post by Ao7bei3s »

corobo wrote: post #47
Ao7bei3s wrote: post #38

Earlier quoted context omitted.

Because A records don't mean complete control over domains. There is a difference between "I can serve content under this domain (currently)" and "I control this domain (and can decide where it points)". DNS domain validation is the right way to do domain validation. But it's slightly harder for users, which is why HTTP(s)- or E-Mail-based validation is being done more often.

I can serve using HTTP on this domain should be enough to prove you can also serve HTTPS on this domain though. It's on the domain owner to avoid giving away control of their (sub)domain to a malicious party. Exactly the same as with regular HTTP and anything else that uses DNS.

It's not about proving that you can serve HTTPS, it's about proving that you can legitimately serve HTTPS.

I'd find HTTP(S)-based validation ok if CAs wouldn't issue certificates with an expiration time past the expiration time of the DNS records.

Of course that would be fairly impractical. But then DNS-based validation exists and doesn't have these problems.

Re: Let’s Encrypt Now Being Abused by Malvertisers

#60

Post by cynix »

Sujan wrote: post #57
pdkl95 wrote: post #32

> gained the ability to create subdomains under a legitimate domain As lots of people in this thread have already pointed out, that's the security problem. The DNS zone that was delegated to you, then you have a responsibility to keep the "squatters" away. > Traffic to this created subdomain was protected with HTTPS Good. HTTP is obsolete. That doesn't change anything from the perspective of the victim. > an open Dou…

> > These DV certificates can help the hacker gain legitimacy with the public. > How? By the lock displayed in the browser that couldn't be there for free that easy before.

StartSSL.
Post reply on HN