Tag: Microsoft

Microsoft Teams is not quite the Team Player we thought

TimeHorse April 30, 2020 No Comments

The folks at CyberArk uncovered a new vulnerability in Microsoft Teams. In Beware of the GIF: Account Takeover Vulnerability in Microsoft Teams, they investigate a serious security hole in Teams that could threaten your organization and provide access to confidential information. Fortunately, Microsoft has, in theory, patched this vulnerability thanks to locking down any vulnerable Microsoft Teams servers.

This is a startling development considering how I’ve had to defend Zoom with respect to its long-ago patched UNC Path vulnerability. Now, we find out that by intercepting the traffic during the sending of images like a Gif, an attacker can subvert a computer’s security, intercept a victims access tokens, and impersonate the victim to begin a social engineering attack.

The basic process is the attacker can use Fiddler to intercept a benign image being transmitted. Since the image is transmitted via its URI, the attacker can modify the packet that transmits the benign URI and change the source domain to come from a compromised Microsoft Teams server.

Next, the attacker needs to intercept traffic to the compromised Microsoft Teams servers. Once the victim loads the image in his Teams viewer, the victim’s computer transmits his authentication tokens to the compromised server and thus the attacker has the users credentials.

The main solution is to lock down any vulnerable servers in the Microsoft Teams subnet. However, it is interesting that Teams uses a REST API with JWT. This is a very common authentication method and one used by OAuth Authentication. I have developed a number of software components that use JWT from OAuth and use those tokens to make connections to various web services I typically use, like meetup and Google Drive.

Microsoft Teams uses two JWT. First, the user gets an authentication token, and with that, the user can get the session token called skypetoken_asm. Both tokens are required by the Microsoft REST API to communicate with the server. The interesting thing, though, is that the second token is called Skype Token. A few years ago Microsoft bought Skype. At the time, people speculated why and of course with Microsoft Teams, I thought it might be leverage Microsoft with its own video conferencing platform. The question was, was Microsoft Teams based on Skype? It looks like at least in part, the answer is yes.

Below, you can watch a video of how this attack might actually work.

Beware of the GIF: Account Takeover Vulnerability in Microsoft Teams | CyberArk

So, be careful what video conferencing system you use. Clearly, Zoom isn’t perfect, but neither is Microsoft, and neither is Google likely to be. There is no reason to pick on any of them. All three are working hard to patch vulnerabilities as soon as they’re found. Just, try to keep your software up to date. And that’s my latest deep dive into Video Conferencing security. If you like what you’ve read, I’m available and eager for hire.

Meetup Online: It’s Okay to Zoom

TimeHorse April 5, 2020 2 Comments

As an Internet Security professional, I have heard some folks expressing dismay over various security issues in the Zoom video conferencing package and the MatterMost chat services. I may do a piece on MatterMost at a later date, but for now I want to focus on Zoom because Zoom is what Meetup is suggesting as one of their preferred video conferencing platforms. (The other, Google Hangouts, is limited to ten people and thus isn’t practical for a number of the meetups I run.)

The thing is, many of the earlier security issues which plagued Zoom at the beginning of the recent surge in online meetings have been solved. Tom’s Hardware wrote a very insightful analysis of these issues in a recent article by Paul Wagenseil, Zoom privacy and security issues: Here’s everything that’s wrong (so far).

Most of the issues covered have already been patched, such as UNC password theft under Microsoft Windows. This was a rather insidious security flaw but fortunately the folks at Zoom stepped up to the plate and patched.

iOS profiling also seems to be fixed. Since I do a lot of my Zoom conferencing, with the National Popular Vote Interstate Compact grassroots coalition, on the iPhone, this has been a great relief. Now, though, I do most of my meetup Zoom conferences on my laptop.

The decrypting of streams at the Zoom servers and re-encrypting them as they go out to the far-end client is at first blush worrisome, but that in part is necessary for folks recording their zoom sessions and though it puts a vulnerability at the level of Zoom staff, one hopes Zoom is careful with whom it employs. But it must be said, nothing I do on Zoom is something I would be embarrassed about were it to leak. I nonetheless want to do everything in my power to make sure it stays secure and I’m happy to hear Zoom is looking into closing this security flaw.

The auto-download for Macintosh is worrisome but again I am happy to say this practice is also ending as it is a backdoor that Zoom can use to allow third party software onto ones Mac. Zoom also has ceased allowing team profiles to share email addresses, though this is not a feature I’m using for any of my Zoom conferences.

As for recording leaking onto the Internet or folks joining your conference uninvited (Zoom Bombing) or war drive scanning Zoom to find your conference, all of these can be solved by user diligence. It’s important to be mindful of who you let into a conference, and don’t let just anyone have access to your recordings. For my Writing Groups, only myself, the account owner, and the persons being reviewed will ever have access to the recordings, and if the reviewed doesn’t need the recordings, we will delete them.

Also, as of this morning, 5 April 2020, at 0:00 UTC, Zoom now requires passwords on all new Zoom events. Thus, even with a Zoom ID scan, you won’t be able to get into the meeting without the password and although the URL can encode the password in an obfuscated way, simply scanning Zoom IDs will not get you into the conferences. And even if you did, I’d still have to approve you. I won’t.

Zoom
The Zoom Logo

Overall, I’m quite happy with Zoom and hope to use it all through Covidapolis. Overall, I give it this Security Engineers line of approval. And please note, I am available for hire if you like what you see!