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Troopers 19 - I am AD FS and So Can You

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Troopers 19 - I am AD FS and So Can You

  1. 1. Douglas Bienstock and Austin Baker I AM AD FS AND SO CAN YOU
  2. 2. ©2019 FireEye©2019 FireEye  Whoami  What is AD FS and how does it work?  How do we find AD FS servers?  How can we attack AD FS?  How can we become (takeover) AD FS?  Tools and Demos  Best practices and mitigations  Goal: Understand AD FS, how we can attack it and why we want to, and how to keep it safe Roadmap
  3. 3. ©2019 FireEye©2019 FireEye  4.5 years of experience at Mandiant  IR and Red Team lead  Speaks fluent cloud Doug Bienstock - @doughsec 3
  4. 4. ©2019 FireEye©2019 FireEye  IR and Red Team  5.5 years at Mandiant  Teaches some classes and stuff  Plays some games and junk Austin Baker - @bakedsec 4
  5. 5. MSFT AD FS – WTF?
  6. 6. ©2019 FireEye©2019 FireEye  Single-Sign On (SSO) solution for applications that don’t integrate directly to Active Directory  In plaintext: use AD creds for services/apps outside AD  Centralizes both authentication, identity management, token issuance  Basically required for any large org now  We must go deeper… Active Directory Federated Services 6
  7. 7. ©2019 FireEye©2019 FireEye  Organizations are increasingly moving to the cloud  AD as a data/security boundary no longer exists  AD FS is commonly the gateway to the cloud for organizations  If we can own AD FS we can own the cloud  As security practitioners we must keep up with the move to the cloud OK – but why do we care? 7
  8. 8. ©2019 FireEye©2019 FireEye  Claims: Statements about a user’s identity – Description (type) and value  Attribute Store: Where claims are sourced from (e.g. AD)  Claims Rules: Business logic that takes incoming claims, apply conditions, and produce new outgoing claims based on those conditions. Applied in the claims pipeline  c:[Type == "http://schemas.microsoft.com/ws/2008/06/identity/claims/windowsaccountname" , Issuer == "AD AUTHORITY"] => issue(store = "Active Directory", types = ("http://schemas.xmlsoap.org/ws/2005/05/identity/claims/emailaddress"), query = ";mail;{0}", param = c.Value); Building blocks 8
  9. 9. ©2019 FireEye©2019 FireEye 1. Start with claims from AD 2. Pipeline adds new claims and modifies existing claims according to rules 3. Outputs set of claims that the relying party has communicated it needs – Claims coming out of the pipeline are transformed into security token attributes 9 Building Blocks - Claims Pipeline
  10. 10. ©2019 FireEye©2019 FireEye  Claims output from the claims pipeline are used to generate security tokens in the form of SAML tokens  Relying parties can be configured with SAML and WS-FED consumers – WS-FED => SAML 1.1 tokens – SAML => SAML 2.0 tokens  The tokens follow a standardized (OASIS) format that we rely on to be consistent  Tokens are accepted by relying parties in a standardized format, too – SAMLResponse POST parameter Building Blocks - Security Tokens 11
  11. 11. ©2019 FireEye©2019 FireEye  c:[Type == "http://schemas.microsoft.com/ws/2008/06/identity/claims/windowsaccountname" , Issuer == "AD AUTHORITY"] => issue(store = "Active Directory", types = ("http://schemas.xmlsoap.org/ws/2005/05/identity/claims/emailaddress"), query = ";mail;{0}", param = c.Value);  <Attribute Name="http://schemas.xmlsoap.org/ws/2005/05/identity/claims/emailaddress"> <AttributeValue>robin@doughcorp.com</AttributeValue> </Attribute> Building Blocks – claims to assertions 12
  12. 12. ©2019 FireEye©2019 FireEye  Identity Provider (IdP): Organization that takes identities as input and outputs claims about them. Authenticates a user, builds claims for that user (the pipeline), and packages them into security tokens  ADFS Service: Our IdP, the "account organization" Building blocks – the IdP 13
  13. 13. ©2019 FireEye©2019 FireEye  AD FS Proxy (WAP): Proxy server that sits in DMZ to receive requests from Internet  Relying Party (RP): Unpacks provided claims from security token and makes authorization decisions based on them. They rely on the provided claims – e.g. a third-party cloud application Building blocks – the RP 14
  14. 14. ©2019 FireEye©2019 FireEye (1) https://portal.office.com (2) 302 sts.doughcorp.com (3)
  15. 15. ©2019 FireEye©2019 FireEye (3) (4) (5) (6) <t:RequestSecurityTokenResponse xmlns:t="http://schemas.xmlsoap.org/ws/2005/02/tru st"> <saml:Assertion xmlns:saml="urn:oasis:names:tc:SAML:1.0:assertion”> <saml:Attribute AttributeName="UPN" AttributeNamespace="http://schemas.xmlsoap.org/cl aims"> <saml:AttributeValue> robin@doughcorp.co</saml:AttributeValue> </saml:Attribute>
  16. 16. ©2019 FireEye©2019 FireEye (1) https://portal.office.com (2) 302 sts.doughcorp.com Login.microsoftonline.com (3) (4) (5) (6) (7)
  17. 17. ©2019 FireEye©2019 FireEye Identity Providers 18
  18. 18. ©2019 FireEye©2019 FireEye  Federations need identity providers – Need to know someone is who they claim to be  AD FS is the nexus of identity provision – And adapters are how third-party vendors can augment that process for their own purposes  Every major vendor with hands in the authentication cookie jar has an AD FS adapter – Some even aim to compete for with AD FS for the IdP crown Identity Providers and Adapters 19
  19. 19. Identifying AD FS
  20. 20. ©2019 FireEye©2019 FireEye  Search DNS for prefixes suggested by Microsoft (most people follow their deploy guides) – adfs.doughcorp.com, sts.doughcorp.com, fs.doughcorp.com – Quick Shodan search found 10,000+  Try logging in to Office 365 using a bogus email address and see if you are redirected  Search for required URL paths – /adfs/ls – /adfs/services/trust/2005/usernamemixed – more… Finding AD FS Proxies 21
  21. 21. ©2019 FireEye©2019 FireEye  Some fun things...  During deployment Microsoft recommends enabling “IDP-initiated sign-on” in order to test – Available at /adfs/ls/idpinitiatedsignon.aspx  Nice forms-based auth for a password spray  Lists SAML-enabled service providers that use AD FS Finding AD FS Proxies 22
  22. 22. ©2019 FireEye©2019 FireEye  AD FS also supports NTLM-based authentication for on-premise users  By default those URLs are also exposed to the Internet via the AD FS proxies  Leaks the internal hostname of the AD FS server (not proxy), including the Active Directory domain name – Also provides another vector for password sprays  /adfs/services/trust/2005/windowstransport  /adfs/services/trust/13/windowstransport  https://docs.microsoft.com/en-us/windows-server/identity/ad-fs/deployment/best-practices-securing-ad-fs Finding ADFS Proxies 23
  23. 23. Attacking AD FS
  24. 24. ©2019 FireEye©2019 FireEye “It’s like the more complex systems we come across, the more attack surface we see.” - Biggie Smalls, maybe 25
  25. 25. ©2019 FireEye©2019 FireEye  Which pieces are obvious targets: – Relying Party supporting apps (Duo, RSA, etc. management) – IdP policies and exceptions (AD FS configurations) – IdP-RP adapters  Relying Party attacks covered in-depth elsewhere – See “Two-Factor, Too Furious” from DerbyCon  The IdP side on the other hand… Target the Weak Links 26
  26. 26. ©2019 FireEye©2019 FireEye  Auth adapters just implement necessary idP methods – IsAvailableForUser, Metadata, OnAuthenticationPipelineLoad/Unload, OnError, TryEndAuthentication – Registered in GAC – signed with strong name  Vendor adapters construct supporting functions for the above – Contain all the logic to determine whether a user's claim is signed off on – Good place to focus attention  Many routes to take – Register new adapters or adjust existing adapters Adapt or die 27
  27. 27. ©2019 FireEye©2019 FireEye Adapt or die 28  Start by investigating Microsoft.IdentityServer.ServiceHost.exe and our DLL
  28. 28. ©2019 FireEye©2019 FireEye Adapt or die 29  Acquire adapter .dll and patch relevant DLL method
  29. 29. ©2019 FireEye©2019 FireEye Adapt or die 30
  30. 30. ©2019 FireEye©2019 FireEye Adapt or die 31
  31. 31. ©2019 FireEye©2019 FireEye32 Adapt or die
  32. 32. ©2019 FireEye©2019 FireEye Adapt or die 33  Kill/suspend service, replace DLL, restart  Verify success!  Depending on adapter: – Different methods to patch – Different logging methods  Same knowledge can be used dynamically – In-memory patching stealthy, more technically complex – Doesn't persistent restarts without a persistent "shim"
  33. 33. Becoming ADFS
  34. 34. ©2019 FireEye©2019 FireEye “The token signing certificate is considered the bedrock of security in regards to ADFS. If someone were to get ahold of this certificate, they could easily impersonate your ADFS server.” - Microsoft 35
  35. 35. ©2019 FireEye©2019 FireEye Mimikatz is for the birds (in this case) 36
  36. 36. ©2019 FireEye©2019 FireEye  Relational database intended to be used only by Microsoft products – MS-SQL “lite” – Default option for AD FS  Accessible over a named-pipe – .pipeMICROSOFT##WIDtsqlquery – Windows 2012+  Can be accessed using SMSS Windows Internal Database (WID) 37
  37. 37. ©2019 FireEye©2019 FireEye  Used by AD FS to store service configuration data in default config  Only accessible by the AD FS service account WID 38
  38. 38. ©2019 FireEye©2019 FireEye  ADFSConfigurationV3.IdentityServerPolicy.ServiceSetting Locating the goods 39
  39. 39. ©2019 FireEye©2019 FireEye  “We present DKM, a distributed key management system with a cryptographically verified code base. DKM implements a new data protection API. It manages keys and policies on behalf of groups of users that share data.” – [https://www.microsoft.com/en-us/research/publication/cryptographically-verified-design- and-implementation-of-a-distributed-key-manager/] DKM 40
  40. 40. ©2019 FireEye©2019 FireEye DKM 41
  41. 41. ©2019 FireEye©2019 FireEye  Upon service start, AD FS will load configuration information from the configuration database (in this case the WID)  As part of that process it calls LoadCertificateCollection()  Which in turn calls DkmDataProtector.Unprotect()... – Passing in base64 decoded blob from EncryptedPFX XML element Decrypting the SigningToken 42
  42. 42. ©2019 FireEye©2019 FireEye  … which in turn calls Dkm.GroupKey._Unprotect() ... – ...which inherits the method from DKMBase Decrypting the SigningToken 43
  43. 43. ©2019 FireEye©2019 FireEye – DKMBase.Unprotect() is where the magic happens Decrypting the SigningToken 44 Decode the EncryptedPFX blob Get key length based on encryption algorithm in use Read the DKM key KDK using DKM key Decryption!
  44. 44. ©2019 FireEye©2019 FireEye Decrypting the SigningToken 45
  45. 45. ©2019 FireEye©2019 FireEye  Uses Key Derivation Function from NIST SP 800-108 in Counter Mode – DKM key is not used itself to decrypt Signing Certificate – Used as initial input for HMAC-SHA256 Key Derivation (NIST SP 800-108)  Mostly, but not exactly, follows the standard (because standards are hard ;) – Context is the Nonce decoded from blob – Label is the OIDs of the encryption algorithms decoded from blob – Outputs keys to use for AES encryption as well as SHA256 HMAC for verification of ciphertext Key Derivation 47
  46. 46. ©2019 FireEye©2019 FireEye  Decrypts using Windows Crypto libraries  AES128 in CBC mode – 16 byte key derived from the DKM key – 16 byte IV decoded from the EncryptedPfx blob  Valid for 1 year!! Key Decryption 48
  47. 47. ©2019 FireEye©2019 FireEye49 Putting it all together 1. EncryptedPFX read from the configuration DB 2. ASN1 types and ciphertext parsed from the blob 3. DKM key read from AD 4. DKM key used for KDF to obtain AES key 5. Ciphertext from EncryptedPFX is decrypted into a PKCS12 object 6. Become an AD FS server – sign our own security tokens
  48. 48. ©2019 FireEye©2019 FireEye  AD FS handles "strong authentication" – MFA – Certs – Blood-oath  If we can issue security tokens, then we can just ignore these requirements  Relying Parties are blind to these requirements anyway, they just want a valid token "But I have MFA so I'm good" 50
  49. 49. Tool Time
  50. 50. ©2019 FireEye©2019 FireEye  https://github.com/fireeye/ADFSDump  .NET Assembly to be run on an AD FS server  Must be run on AD FS server as the AD FS service account  Dumps information from the configuration database and AD needed to generate signed security tokens and become ADFS :) – Encrypted PFX – DKM group key – Relying parties – Issuance rules ADFSDump 52
  51. 51. ©2019 FireEye©2019 FireEye  https://github.com/fireeye/ADFSpoof  Python program to be run offline – Designed to be run using the data obtained from ADFSDump  Decrypts EncryptedPfx blob given a DKM key  Generates signed SAML tokens for arbitrary users that can be sent to a Relying Party – Uses user-generated XML templates – Each template requires specific parameters – the claims contained in the RP issuance rules – Launching with Office 365, Dropbox, and extensible SAML 2.0 templates ADFSpoof 53
  52. 52. ©2019 FireEye©2019 FireEye54
  53. 53. Best Practices and Mitigations
  54. 54. ©2019 FireEye©2019 FireEye  Secure privileged access –The AD FS server should be treated as a Tier 0 device (like a domain controller) – Access should be restricted to only originate from privileged access workstations  Enabled advanced auditing on AD FS – Check “success” and “failure” audit options in AD FS Management snap-in – Enable “Audit Application Generated” events on the AD FS farm via GPO Best Practices and Mitigations 56 Before everything goes awry
  55. 55. ©2019 FireEye©2019 FireEye  Make the AD FS Service account a gMSA – Passwords managed by AD  High Security: Use a Hardware Security Module (HSM)  While we're at it: Extranet Smart Lockout for AD FS 2016 Best Practices and Mitigations 57 Before everything goes awry
  56. 56. ©2019 FireEye©2019 FireEye  Identity providers now are part of the incident response process  If you have good visibility and confidence attacker targeted AD FS: – Reset signing key - carefully – Compare claims rules/exceptions against baselines – Verify core adapters are intact  If not – determine your risk rating and act appropriately  Vendor debug logs can be useful in AD FS cloning scenarios – Not so much with modified adapters... Responding Appropriately 58
  57. 57. FIN

Editor's Notes

  • Our goal for you at the end of the talk: Understand how AD FS works, how to attack AD FS and why it is an attractive target for attackers, and how we can keep AD FS safe
  • So before we can dive into attacking AD FS we need to understand it. Welcome to the whirlwind tour of AD FS
  • At its most basic AD FS can be defined as…
    Lets unpack how this actually works
  • Before we dive in lets answer an important question – why are we even here? I always find it a good idea to discuss motivations for a talk/research
  • So let's begin our tour
    - the currency of AD FS is claims. Claims are statements that tell us about a user's identiy
    - they are going to come from an attribute store, in most cases Active Directory
    Claims are acted on by rules which follow a speicfic language
         - conditions
        - statements
    These rules are collected into a pipeline
  • A very simplified view of our pipeline
    - don’t really care about the first inputs
    - the last set of rules issuance rules, are what we care about
    The output of the issuance rules is the final set of claims that makes its way into the security token
  • In our previous example use case, the bulk of what AD FS does is when it sources claims (statements about an identity), and processes them into a security token. That process is called the claims pipeline
    There are three main stages to the pipeline
    After the third stage we have claims that are ready to be packaged into a usable security token
  • The security tokens are what a relying party is going to ultimately consume
  • Some key terms to be know before we go further
    Lets understand how these different terms come into play with an example use case
  • Some key terms to be know before we go further
    Lets understand how these different terms come into play with an example use case
  • A typical example of the WebSSO authentication flow using AD FS
    User navigates to https;//login.microsoftonline.com
    They type in their organization email address and O365 issues a 302 redirect to the AD FS URL, sts.doughcorp.com
    The AD FS proxy opens a connection to the AD FS server, presenting a web auth form
    The user types in their email address and AD password into the web form
    The ADFS server talks to the claim’s provider attribute store, AD to authenticate the user
    Upon successful auth, the federation service receives claims from the claims provider, and puts them through the claims pipleline The pipeline checks if the user is authorized, transforms the claims and generate a signed security token
    The user’s browser receives the security token and sends it to Office 365 where it is verfieid and exchanged for a usable authentication token (a session cookie)
  • A typical example of the WebSSO authentication flow using AD FS
    User navigates to https;//login.microsoftonline.com
    They type in their organization email address and O365 issues a 302 redirect to the AD FS URL, sts.doughcorp.com
    The AD FS proxy opens a connection to the AD FS server, presenting a web auth form
    The user types in their email address and AD password into the web form
    The ADFS server talks to the claim’s provider attribute store, AD to authenticate the user
    Upon successful auth, the federation service receives claims from the claims provider,  and puts them through the claims pipleline The pipeline checks if the user is authorized, transforms the claims and generate a signed security token
    AD FS retrieves these attribute values from the store and creates claims based on that information
    The user’s browser receives the security token and sends it to Office 365 where it is verfieid and exchanged for a usable authentication token (a session cookie)
  • A typical example of the WebSSO authentication flow using AD FS
    User navigates to https;//login.microsoftonline.com
    They type in their organization email address and O365 issues a 302 redirect to the AD FS URL, sts.doughcorp.com
    The AD FS proxy opens a connection to the AD FS server, presenting a web auth form
    The user types in their email address and AD password into the web form
    The ADFS server talks to the claim’s provider attribute store, AD to authenticate the user
    Upon successful auth, the federation service receives claims from the claims provider, and puts them through the claims pipleline The pipeline checks if the user is authorized, transforms the claims and generate a signed security token
    The user’s browser receives the security token and sends it to Office 365 where it is verfieid and exchanged for a usable authentication token (a session cookie)
  • We already talked about how AD FS transforms a user authentication event into a security token which is sent to the relying party
    Now we are going to go just a little deeper to understand how AD FS itself is architected
    Mention: MSSQL DB another option for structured data storage
  • When you set up AD FS authentication is configured to only allow the service account
    Not even a DA will be able to access the database in its base configuration
  • Exploring this configuration database we can see a table ServiceSetting
    It contains a single row, whose data is a large XML doc
    Perusing that document we see a tag “SigningToken” with a child element of “EcnryptedPfx”
    Well that looks interesting doesn’t it
  • - If you look at the XML document from ServiceSetting table it also contains a tag called “DKMsetting” which I thought was interesting
    A quick google search showed that it is related to encryption, interesting..
    In fact, AD FS uses DKM to store an symmetric key that we can use to decrypt that “EncryptedPFX” blob
  • Opening up AD explorer we can see the container stored as the following
    And we can see besides the groups we would eexpect (DA, EA, etc) the AD FS service account also has read/write permissions over this object..
    So lets try and piece together how the DKM key is used to decrypte the Encrypted Signing Token by doing a code walk
  • AD FS is written entirely in .NET, so we can easily inspect the code using tools such as DnSpy
    Eventually we can trace to the LoadCertificateCollection() function
    First it tries to load the certificates from the cert store, which is where they get placed after the first service start
    If that fails however we can see it reads the EncryptedPFx value, decodes it and then passes it to this “Unprotect” method of the _protector clas
    _protector is actually of type DKMDataProtector… we are on the right track
  • We can see that Unprotect is calling another Unprotect method from a _dkm attribute
    This is of type Dkm.Groupkey so we are still on the hunt..
  • - Finally in the DKMBase class we can see where the magic happens
    Unprotect method here is doing a lot of tings
    It turns out that the EncryptedPFx binary blob is not a simple data type. Rather it is binary data containing ASN1 types
    Those ASN1 types contain important information needed to decrypt the signing certificate. Things the IV for the decryption method, the alrogithm types, and a MAC code for verification
    We can also see that the DKM key stored in AD is not actually the decryption key. Rather it serves as input for a Key Derivation function that is used to obtain the actual key we need
  • We can see here an overview of an example EncryptedPFx binary blob and the different encoded ASN1 types.
    The decodeprotectedblob() function is unpacking all these structures
  • Following the ReadKey method we can see how DKM is acutally used to store data
  • The key derivation is using the standard Microsoft crypto library
    From the name we can see it should follow the NIST standard SP 800-108
    After tracing the code I found it is a very close follower of the standard, but not quite 
  • Finally we understand how this works
    The EncryptedPFX base64 data is read and decoded from the config database
  • ×