The linked CVE has something that strikes me as odd. It marks this exploit's 'Attack Complexity' as 'High', meaning:
> A successful attack depends on conditions beyond the attacker's control. That is, a successful attack cannot be accomplished at will, but requires the attacker to invest in some measurable amount of effort in preparation or execution against the vulnerable component before a successful attack can be expected. For example, a successful attack may require an attacker to: gather knowledge about the environment in which the vulnerable target/component exists; prepare the target environment to improve exploit reliability; or inject themselves into the logical network path between the target and the resource requested by the victim in order to read and/or modify network communications (e.g., a man in the middle attack).
But reading Dirk-jan's article, really all you need is basic admin knowledge of Entra ID etc., and the netId of any single user on the targetted environment, which can be found using brute force enumeration. The rest is public knowledge.
Strictly speaking the attacker would need to invest in some measurable amount of effort, but that seems like stretching the definition to make the CVE look less awkward.
Arch-TK 4 hours ago [-]
In my personal experience as someone who has spent the last 6 years of his career in the security industry, almost nobody actually uses CVSS the way it is intended, they just almost arbitrarily tweak the CVSS inputs to produce an output they like.
You are correct that the attack complexity probably shouldn't be high in this case. But presumably the person calculating the CVSS score thought it was too high if attack complexity wasn't set to high.
CVSS has other issues, like people trying to apply it to things that are not vulnerabilities. I would ignore most CVSS scores you see and just read what the issue is instead and make your own judgement call.
lucasRW 3 hours ago [-]
"really all you need is basic admin knowledge of Entra ID"
> Yes, because any "basic user of Entra ID with basic knowledge of it" has found undocumented types of tokens, and stringed them with another Graph API vulnerability, to impersonate users...
Basic Entra ID users don't even know what an Entra ID token is exactly.
Freak_NL 3 hours ago [-]
Having knowledge of the exploit itself does not seem to factor in to determining the complexity of the exploit. Rather, it appears to document the complexity of executing it against any given target, given that the exploit is known to the attacker (and someone else has done the hard work of finding it). See the 'A successful attack depends on conditions beyond the attacker's control.' part in the documentation of 'high'.
In this exploit, there are hardly any conditions beyond the attacker's control which must be satisfied.
nl 6 hours ago [-]
Well at least someone could log in using Entra ID!
userbinator 10 hours ago [-]
failed to properly validate the originating tenant
One wonders whether those who designed all this ever considered what that field in the token is for.
The word "tenant" is also very telling --- you're just renting, and the "landlord" always has the keys.
nine_k 8 hours ago [-]
It's even worse: "Because of the nature of these Actor tokens, they are not subject to security policies like Conditional Access". This goes against all principles of good security design. A token that gives root access instead of specifying a particular action allowed just invites misuse, erroneous or malicious.
I would expect these tokens to be like JWT or macaroons, carrying specific permissions within specific bounds / tenants. Alas.
milkshakes 7 hours ago [-]
well, you're in luck, they are JWTs in fact. JWTs in JWTs, so extra secure.
Freak_NL 4 hours ago [-]
And of course, because the inner JWT is already signed, why bother signing the outer one? Just validate the inner one!
I'm feeling sorry for those poor abused JWTs in this vulnerability.
Nursie 7 hours ago [-]
They are!
But the systems that have been built around them are bad. Firstly in issuing these ‘root’ tokens at all, and secondly in not checking the claims properly.
A JWT is only as good as the systems it’s used by.
viraptor 1 hours ago [-]
It's the standard naming for the services. Multi-tenancy is a thing, but landlords are not in this naming context.
This makes me wonder if Microsoft’s commitment to long-term support is part of the problem: instead of deprecating these ancient APIs they keep them on life-support, but forget some "regression-test" on how they interact with the shiny new surfaces.
Feels like P0’s Windows Registry talks, most of the vulns weren’t in the new code, they were in the how legacy behaviors interacted with newer features.
tonyhart7 4 hours ago [-]
Microsoft also forced to keep these legacy code tbh
You see, most enterprise client with big enough contract can force to do this and MS need to support this customer until they migrate or if they ever be at all
I may argue for any big legacy enterprise software, its easier to rewrite the damn whole thing than to support the legacy code forever but they cant do that even if they have motivation/resource
the8472 3 hours ago [-]
They could put it behind a flag, like LANMAN auth.
pcj-github 9 hours ago [-]
Absolutely insane. Security so weak, it seems like you discovered an intentional backdoor.
> impersonation tokens, called “Actor tokens”, that Microsoft uses in their backend for service-to-service (S2S)
Literally every single "security" framework uses God-mode long-lived tokens for non-human identities.
(Except for SPIFFE, but that's a niche thing and used only for Kubernetes bullshit.)
The whole field of "security" is a farce staffed by clowns.
cyberax 5 hours ago [-]
AWS had switched from using something like this ("injection tokens") to just regular IAM roles, though managed by the AWS.
The only special permission that services (actually, the AWS accounts that they use) inside the AWS have is access to "service principals". The service roles inside customer accounts then use them to grant access.
AWS IAM is painful, but it shows that you can design a secure permission system.
otabdeveloper4 3 hours ago [-]
You can add many layers of indirection, but unless you're actually authenticating that a system service is using the credentials (and not, say, a user or a script) then it boils down to a long-lived token at the end.
noctune 1 hours ago [-]
You can condition IAM on Nitro attestation, so that's doable (if a lot more work than usual).
rootsudo 10 hours ago [-]
Oh man, I was close with this a few times as I ran powershell in different ISE windows and sometimes copied/pasted things over for different tenants, darn - it really seemed so obvious of an exploit!
gfody 8 hours ago [-]
after 36 years kerberos seems pretty stable, secure, and well supported finally. why do we need Entra?
EvanAnderson 7 hours ago [-]
Kerberos doesn't have a good monthly recurring revenue "story".
jiggawatts 6 hours ago [-]
Kerberos doesn't work well on the web.
zbentley 3 hours ago [-]
Citation needed. Other than throughput/reliability risks posed by the revocation check flow (which I know aren’t the reason people don’t use Kerberos on the web, since the big auth providers’ SPOFiness in this area is way worse, as proven by countless outages induced by so-and-so rickety auth component failing bringing down a major provider), Kerberos’ adoption issues on the web have more to do with network effect and monetization than technical limitations with the protocol.
Sytten 6 hours ago [-]
I recently had to deal with Entra ID for the first time to setup Microsoft OAuth for our site and my god why is it so badly designed.
Just creating a tenant is a PITA and you get a default tenant you can't change without paying for Microsoft 365? Then you have subscriptions, Microsoft partners, Enteprise vs individual accounts, etc. All mixed with legacy AD naming and renaming, documentation with outdated screenshots, Microsoft Partners bullshit.
7bit 2 hours ago [-]
> Just creating a tenant is a PITA and you get a default tenant you can't change without paying for Microsoft 365?
What exactly ist a PITA when creating a tenant? It's straightforward.
And what do you mean by default tenant that you cannot change unless you pay? Nothing comes to mind where that would be the case.
Are you sure you're not just using it wrong?
Propelloni 6 hours ago [-]
There ist a whole industry clustered around this FUBAR that makes its living by helping companies navigate this shit. It has small and big players and they have no incentive to tell you that there is anything else you could use. The monthly Service fee is too tasty.
2 hours ago [-]
malnourish 8 hours ago [-]
I imagine this paid out quote the bounty; exploited, it's hard to think of a more damning security flaw.
cr125rider 10 hours ago [-]
Wow the keys to all the enterprise castles! That’s wild!
> A successful attack depends on conditions beyond the attacker's control. That is, a successful attack cannot be accomplished at will, but requires the attacker to invest in some measurable amount of effort in preparation or execution against the vulnerable component before a successful attack can be expected. For example, a successful attack may require an attacker to: gather knowledge about the environment in which the vulnerable target/component exists; prepare the target environment to improve exploit reliability; or inject themselves into the logical network path between the target and the resource requested by the victim in order to read and/or modify network communications (e.g., a man in the middle attack).
But reading Dirk-jan's article, really all you need is basic admin knowledge of Entra ID etc., and the netId of any single user on the targetted environment, which can be found using brute force enumeration. The rest is public knowledge.
Strictly speaking the attacker would need to invest in some measurable amount of effort, but that seems like stretching the definition to make the CVE look less awkward.
You are correct that the attack complexity probably shouldn't be high in this case. But presumably the person calculating the CVSS score thought it was too high if attack complexity wasn't set to high.
CVSS has other issues, like people trying to apply it to things that are not vulnerabilities. I would ignore most CVSS scores you see and just read what the issue is instead and make your own judgement call.
> Yes, because any "basic user of Entra ID with basic knowledge of it" has found undocumented types of tokens, and stringed them with another Graph API vulnerability, to impersonate users...
Basic Entra ID users don't even know what an Entra ID token is exactly.
In this exploit, there are hardly any conditions beyond the attacker's control which must be satisfied.
One wonders whether those who designed all this ever considered what that field in the token is for.
The word "tenant" is also very telling --- you're just renting, and the "landlord" always has the keys.
I would expect these tokens to be like JWT or macaroons, carrying specific permissions within specific bounds / tenants. Alas.
I'm feeling sorry for those poor abused JWTs in this vulnerability.
But the systems that have been built around them are bad. Firstly in issuing these ‘root’ tokens at all, and secondly in not checking the claims properly.
A JWT is only as good as the systems it’s used by.
Great talk, by the way.
This makes me wonder if Microsoft’s commitment to long-term support is part of the problem: instead of deprecating these ancient APIs they keep them on life-support, but forget some "regression-test" on how they interact with the shiny new surfaces.
Feels like P0’s Windows Registry talks, most of the vulns weren’t in the new code, they were in the how legacy behaviors interacted with newer features.
You see, most enterprise client with big enough contract can force to do this and MS need to support this customer until they migrate or if they ever be at all
I may argue for any big legacy enterprise software, its easier to rewrite the damn whole thing than to support the legacy code forever but they cant do that even if they have motivation/resource
Literally every single "security" framework uses God-mode long-lived tokens for non-human identities.
(Except for SPIFFE, but that's a niche thing and used only for Kubernetes bullshit.)
The whole field of "security" is a farce staffed by clowns.
The only special permission that services (actually, the AWS accounts that they use) inside the AWS have is access to "service principals". The service roles inside customer accounts then use them to grant access.
AWS IAM is painful, but it shows that you can design a secure permission system.
Just creating a tenant is a PITA and you get a default tenant you can't change without paying for Microsoft 365? Then you have subscriptions, Microsoft partners, Enteprise vs individual accounts, etc. All mixed with legacy AD naming and renaming, documentation with outdated screenshots, Microsoft Partners bullshit.
What exactly ist a PITA when creating a tenant? It's straightforward.
And what do you mean by default tenant that you cannot change unless you pay? Nothing comes to mind where that would be the case.
Are you sure you're not just using it wrong?