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> Zerotier promptly addressed the root server identity verification issues. This attack is still possible (as of 20/09/2021); however, an attacker is required t
by api 5y ago
> Zerotier promptly addressed the root server identity verification issues. This attack is still possible (as of 20/09/2021); however, an attacker is required to invest significant compute time (many many years with a single RTX2070) to generate a valid identity that collides with an intended target. Zerotier client’s still accept any identity learned via WHOIS packet as implicitly valid.
ZeroTier founder here:
Clients accept identities learned from WHOIS via root servers, but not from regular nodes.
As mentioned in the writeup, this was reported and fixed rapidly. I don't think there is any remaining issue here, but I am doing a re-read and will publish a blog post in a bit.
It's also important to note that the original (fixed) issue also required a node to be offline for >30 days. So the attacker would have to know your network and the identity of a node that was has not been online for a long time and invest >$500K worth of GPU compute power (at current cloud rates) per identity target.
The certificate thing mentioned is well known and hasn't been considered a vulnerability because certificates of membership are not secrets. They are akin to the SSL server and client certificates presented on SSL connection. That being said, it wouldn't be a bad idea (defense in depth) to make it harder to get these to make enumeration more difficult. We're looking at some mechanisms for this in new versions of ZeroTier.
- _hyn3 5y agoIt's a good point that the cost could (would always?) be high, because you could probably just park a van outside the target's wifi network, given the sad state of wireless crypto. However, ZeroTier is designed to provide encryption on top of an existing network, so by targeting ZT, you gain access to everything within that network, even in other locations. Is the ZeroTier root code open source? Can someone run their own root servers?
- api 5y agoThe root code is open source. That's how they found the issue. We always encourage our users not to (just) trust ZeroTier, not because we don't think it's safe but because you should never trust just one thing. Never, never, never. One layer of security is no security. There are people who will tell you their software could contain bugs. Then there are people who will lie, or who are delusional. Anything you care about should be gated by at least two security systems, preferably ones with different code bases from different vendors. Bonus points if they use different mechanisms or algorithms.
- voidmain 5y agoAs I read TFA, the attack would take ~128 GPU-years to break most or all ZeroTier addresses, not per target. And the author says that there is plenty of room for optimization. And fpga or whatever might be much cheaper than GPU. And "attacks only get better."
- api 5y agoAbsolutely true, which is why the root cause is now fixed. The proof of work component of ZeroTier addresses is a defense in depth measure and was not intended to be a primary defense. It's meant to increase the cost of an attack if other defenses fail to reduce the pool of potential attackers.