Spring Ring: Yet Another Bloody Way Microsoft Teams Can Help Wreck Your Domain
Right, so here’s the deal. Some clever bastards found a nasty attack chain called Spring Ring that turns a Microsoft Teams call into a stepping stone for domain compromise. Because apparently it wasn’t enough for Teams to be annoying, bloated, and forever demanding updates at the worst possible time — now it can help torch your bloody Active Directory too.
The attack abuses how Windows negotiates authentication during certain call scenarios. In short: an attacker can manipulate a target into leaking Net-NTLMv2 hashes during a Teams interaction. And once you’ve got those, you’re off to the races with relay attacks and other delightful piles of shit that can end with privilege escalation and, in the worst case, full domain compromise.
The ugly bit is that this doesn’t require some user to download “totally_not_malware.exe” from a dodgy website run out of a shed. No, this can happen through the normal muck of business communication — a Teams call. That’s what makes it dangerous: it’s piggybacking on something users already trust, which is always where the best security disasters start.
The article explains that the attacker can exploit how the victim’s machine handles authentication requests triggered through Teams-related behavior. If the environment still allows legacy or weak authentication paths, and if mitigations like SMB signing, Extended Protection, or proper NTLM hardening aren’t in place, the attacker may be able to relay credentials to other services and start pulling on threads until the whole miserable jumper unravels.
So what’s the practical takeaway, apart from “Microsoft strikes again”?
First, disable or restrict NTLM wherever possible. Yes, I know, some fossilized line-of-business app from 2009 will scream and die. Good. Let it. Second, enforce SMB signing and review any systems that still accept relayed authentication like it’s 2003. Third, tighten up Teams external access and who can call whom, because maybe letting any random git ring your staff isn’t the pinnacle of defensive architecture. Fourth, monitor for weird authentication attempts, especially outbound SMB/WebDAV-style nonsense linked to collaboration tools.
And of course, patch the relevant systems and pay attention to Microsoft’s guidance, assuming you can decipher the usual corporate word salad without throwing your monitor through a window. The point is simple: if your environment still has old authentication crap hanging around, Spring Ring can chain that weakness into something properly catastrophic.
In summary: Teams calls can be weaponized to coerce credential leakage, those credentials can potentially be relayed, and your half-neglected Windows estate can then hand over the keys to the kingdom if you haven’t done the boring hardening work. Same old story: convenience first, security later, and then everyone acts shocked when the castle is on fucking fire.
I once saw an admin leave NTLM wide open because disabling it might “impact user experience.” Two weeks later, the user experience mainly involved forensics, password resets, and a manager asking why the file servers were speaking Russian. Funny how that works.
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