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WhatsApp Security Vulnerability

schneier.com

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Re: WhatsApp Security Vulnerability

#21

Post by wyldfire »

ikeboy wrote: post #4
wyldfire wrote: post #3

Even if they changed this specific design decision/vulnerability, it seems like there's a big gaping hole (or I'm missing something). Given that WhatsApp brokers the initial key exchange, lawful interdiction can take place at WhatsApp under subpoena. What we hope is the case is that WhatsApp would fight these orders in court, claiming that the keys are merely forwarded and aren't stored by design. But if they fought…

I'd assume the keys are generated on device.

Presumably the device generates a keypair and then needs to exchange with the remote device somehow? I assumed both devices connect to WhatsApp and it delivers what is ostensibly the pub keys from each of the parties to each of them?

Re: WhatsApp Security Vulnerability

#22

Post by pfg »

wyldfire wrote: post #21
ikeboy wrote: post #4

Earlier quoted context omitted.

I'd assume the keys are generated on device.

Presumably the device generates a keypair and then needs to exchange with the remote device somehow? I assumed both devices connect to WhatsApp and it delivers what is ostensibly the pub keys from each of the parties to each of them?

This can be detected if the sender and the recipient attempt to verify their keys out of band (i.e. in person or through some other trusted communication channel). WhatsApp allows you to do that.

Re: WhatsApp Security Vulnerability

#23

Post by wyldfire »

mschuster91 wrote: post #9
tptacek wrote: post #6

Earlier quoted context omitted.

They are, so I'm not sure I understand the attack upthread.

A plausible attack scenario, outlined in multiple steps: 1) Police arrest a drug dealer, who manages to turn his phone off by smashing it on the floor and the battery pops out, in the same step also locking the data from readout if the device is using FDE 2) Cops now take the SIM card, compel the provider to provide the PUK to unlock the SIM card and insert it into their own smartphone 3) Cops activate WhatsApp and n…

That doesn't match the scenario I was describing. Though I think it does match the one described in the article.

Re: WhatsApp Security Vulnerability

#24

Post by xorcist »

aylons wrote: post #14

While people discuss about a possible state-actor stronghanding WhatsApp and the semantics of backdoor, the "design feature" of not showing the key changes are making real victims, at least in Brasil: The attacker first try to duplicate the mobile phone number of the first victim, probably by social engineering their phone company. This part may look difficult to do, but it is not hard if you realize you do not need…

> WA has no login, no password, so anyone receiving the SMS can impersonate anyone

That sounds like a fatal flaw. Could not any GNU Radio user dump these by the thousands?

Re: WhatsApp Security Vulnerability

#25

Post by agd »

The question for me is that posed by the hacker who discovered the vulnerability. Here's what he said [1]:

"He (Moxie) said: “The choice to make these notifications ‘blocking’ would in some ways make things worse. That would leak information to the server about who has enabled safety number change notifications and who hasn’t, effectively telling the server who it could man-in-the-middle transparently and who it couldn’t; something that WhatsApp considered very carefully.”

This claim is false. Those “blocking” clients could instead retransmit a message of the same length that just contains garbage and this message would just not be displayed by the receiver’s phone. Encryption guarantees the garbage or real messages are indistinguishable in the encrypted form. Hence, this technique would make identifying users with the additional security enabled on a large scale impossible."

This was raised in the previous WhatsApp vuln thread but as far as I'm aware, Moxie is yet to address this criticism. Would be good to get a response on this.

[1] https://www.theguardian.com/technology/2017/jan/16/whatsapp-...

Re: WhatsApp Security Vulnerability

#26

Post by dingaling »

pfg wrote: post #22
wyldfire wrote: post #21

Earlier quoted context omitted.

Presumably the device generates a keypair and then needs to exchange with the remote device somehow? I assumed both devices connect to WhatsApp and it delivers what is ostensibly the pub keys from each of the parties to each of them?

This can be detected if the sender and the recipient attempt to verify their keys out of band (i.e. in person or through some other trusted communication channel). WhatsApp allows you to do that.

Out of band but not out of app. It's the WhatsApp app that generates and presents the 'security code' or key fingerprint for comparison.

It's not like SSH in which separate and discrete components generate the keypair and verify fingerprint on connection.

Re: WhatsApp Security Vulnerability

#27

Post by pfg »

dingaling wrote: post #26
pfg wrote: post #22

Earlier quoted context omitted.

This can be detected if the sender and the recipient attempt to verify their keys out of band (i.e. in person or through some other trusted communication channel). WhatsApp allows you to do that.

Out of band but not out of app. It's the WhatsApp app that generates and presents the 'security code' or key fingerprint for comparison. It's not like SSH in which separate and discrete components generate the keypair and verify fingerprint on connection.

That's moving the goalposts. A backdoor in the app itself is a whole different matter - both legally (give us these records/change these records in your database vs. build software according to our spec and ship it to your customers, which is similar to Apple vs. FBI and might not be constitutional) and technically.

I also don't see the difference between this and SSH. If your SSH server or client is backdoored/compromised, you have no control over what happens with your plaintext, no matter what the fingerprint verification tells you. The only difference is that one is open source, so the likelihood that a backdoor is detected is probably higher, though I don't think this means a) there is no backdoor and b) a backdoor in a closed-source app cannot be detected.

Re: WhatsApp Security Vulnerability

#28

Post by MichaelGG »

xorcist wrote: post #24
aylons wrote: post #14

While people discuss about a possible state-actor stronghanding WhatsApp and the semantics of backdoor, the "design feature" of not showing the key changes are making real victims, at least in Brasil: The attacker first try to duplicate the mobile phone number of the first victim, probably by social engineering their phone company. This part may look difficult to do, but it is not hard if you realize you do not need…

> WA has no login, no password, so anyone receiving the SMS can impersonate anyone That sounds like a fatal flaw. Could not any GNU Radio user dump these by the thousands?

Is it true? It'd be trivial to require the activator to be the same device that requested the SMS.

Re: WhatsApp Security Vulnerability

#29

Post by aidenn0 »

noja wrote: post #17
frabbit wrote: post #11

Earlier quoted context omitted.

Or to re-phrase: This security application is not secure but it is usable.

There is no "secure", it's a scale from "no security" to just "very high security".

Security isn't either a scale or a binary; from one point of view a large number of binary values.

Either your security will or won't be compromised by a given threat model. This is binary, but there's lots of different threat models one could have.

e.g. If you care about the Russian government impersonating you, it's a different threat model than if you care about the US government reading your communication, which is a different threat model than if you care about a private actor encrypting all your data and holding it ransom.

This is then complicated by the fact that we can't see into the future (sufficiently complicated code is likely to have bugs, we need to predict if those bugs will be exploited before they are fixed; large government attackers may or may not know about math that the public crypto community doesn't; which governments will successfully compel a third party to do various things or reveal various secrets &c.) so each binary value for the security becomes probabilistic.

Re: WhatsApp Security Vulnerability

#30

Post by WhitneyLand »

StavrosK wrote: post #18
aylons wrote: post #14

While people discuss about a possible state-actor stronghanding WhatsApp and the semantics of backdoor, the "design feature" of not showing the key changes are making real victims, at least in Brasil: The attacker first try to duplicate the mobile phone number of the first victim, probably by social engineering their phone company. This part may look difficult to do, but it is not hard if you realize you do not need…

Unfortunately, if WhatsApp did defend against this, it would be such a big hassle that users would disable it. How many people do you know that wouldn't just click "accept" on "this user's keys changed", or wouldn't just ask the attacker "hey did you get a new phone?" "yes" "oh okay"? People love to blame WhatsApp, but what can anyone realistically do?

No, this is why I disagree with Moxie, the right UI design wouldn't have to create fatigue. It could just block by default, and then allow you to change the default with an appropriate warning.

At least that way, everyone will become aware at least once and make their choice.

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