Disruptive Telephony

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From the Can-We-Please-Communicate-Better Department... there is apparently an open vulnerability in the Skype for Mac client that lets an attacker send a message to a Skype user and gain remote access. As reported today by Gordon Maddern on the PureHacking blog:

The long and the short of it is that an attacker needs only to send a victim a message and they can gain remote control of the victims Mac. It is extremely wormable and dangerous.

Given that I basically live inside of Skype for Mac and use it extensively every day, this is obviously extremely concerning. Particularly because I do let anyone on Skype send me messages... and my Skype ID is easily found on my websites and many other locations (and since is rather obvious - "danyork"). I also tend to leave Skype running on a Mac in my home office that is online all the time. Mostly this provides a way to quickly catch up on chats as I have all the messages already there on that system (rather than waiting for Skype to sync up after it is launched).

Maddern indicates that he contacted Skype over a month ago about this and no fix has come out yet. In his post, he says:

Pure Hacking wont give specifics on how to perform this attack untill a patch from skype is released. However we will give a full disclosure after skype takes action or a resonable responsible disclosure time.

Which is great... except that now attackers will be out there trying to figure out what kind of "payload" he sent that created this condition. There is always the chance that someone may discover the attack.

Where is Skype's Statement?

ZDNet UK covered the story today and received this update from Skype:

Skype has just sent ZDNet UK a statement promising a fix next week. The statement reads: "We are aware of this and will release a fix early next week to resolve the issue. We take our users privacy very seriously and are working quickly to protect Skype users from this vulnerability."

What is concerning, though, is that there is no other public comment on this from Skype...

• ... nothing on Skype's blogs, particularly their Security blog
• ... nothing on Skype's Twitter account
• ... nothing on Skype's SECURITY Twitter account

It's Friday afternoon here in the US... people are about to leave their offices and some % of those who use Macs may in fact leave their computers on and leave Skype running. Are those machines vulnerable? Can someone really just send someone a message and gain control of their Mac?

Which version of Skype for Mac is vulnerable? Is this only in the newer 5.x client? Or does this impact the older 2.8 client?

We need answers, Skype! I can understand that a fix may take some time, but in the meantime we need to understand what the risk is. Are there mitigating circumstances? Or actions we can take in the meantime?

How To (Maybe) Protect Yourself

So what are we to do until there is either a fix or a helpful statement?

1. QUIT OUT OF SKYPE - Obviously this is one option (and one I might pursue on that computer in my office). But that may not be practical for folks... and isn't for me in my work context.

2. CHANGE PRIVACY SETTINGS - It seems to be the biggest change we can make is to only allow chat messages from people in our contact list. This would mean that a random attacker out on the Internet couldn't just send you a message and take over your Mac. You will only get chat messages from your contacts, not random people.

In Skype 5.x for the Mac, you go to the Skype menu and then Preferences and then make sure that the settings are that only Contacts can contact you:

On the Skype 2.8 for Mac client, the layout is a bit different but the choices are similar:

Now, in these images I'm only suggesting you restrict chat messages. In the blog post about the attack, it is very clear that the attack vector is a chat message, so in theory you should only need to change the one privacy option for chat messages. Whether or not you also want to restrict calls to be from your contacts is up to you. Absent a clear statement about the vulnerability from Skype, we have very limited information to go on... but again the blog post was very clear that the attack was through a chat message with a particular payload.

Will that protect your system? I don't know... I'm guessing along with you all.

Now, depending upon how paranoid your mind operates, there is, of course, the case that an attacker could take over a Mac operated by one of your contacts, and then potentially use the Skype client on that machine to then contact you. Maybe that's possible, maybe that's not.

3. RUN AN OLDER SKYPE VERSION - Does this only affect the newer Skype 5.x for MacOS X? Could we be protected by reverting to the older 2.8 client? (which I'm still running on one of my systems)

I don't know... and I wouldn't use this as my only protection mechanism.

Give us a clue, Skype!

We don't know... and that's not a good space to be in.

What can you tell us who are Mac users, Skype?

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UPDATE #1 - The Register also covered the story and pointed out that perhaps the attacking chat message could cause other chat messages to be sent out. Again... possible... but we just don't know.

Also, someone pointed out that Skype did have a "public statement", so my title is not accurate. Sure... they gave a statement to ZDNet UK and perhaps other media outlets... but where is that on Skype's public presence? Why not on one of their blogs or on Twitter?

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