Windows Privilege Escalation
Introduction to Windows Privilege Escalation
After gaining a foothold, elevating our privileges will provide more options for persistence and may reveal information stored locally that can further our access within the environment. The general goal of Windows privilege escalation is to further our access to a given system to a member of the Local Administrators group or the NT AUTHORITY\SYSTEM LocalSystem account. There may, however, be scenarios where escalating to another user on the system may be enough to reach our goal. Privilege escalation is typically a vital step during any engagement. We need to use the access obtained, or some data (such as credentials) found only once we have a session in an elevated context. In some cases, privilege escalation may be the ultimate goal of the assessment if our client hires us for a "gold image" or "workstation breakout" type assessment. Privilege escalation is often vital to continue through a network towards our ultimate objective, as well as for lateral movement.
That being said, we may need to escalate privileges for one of the following reasons:
1.
2.
To escalate privileges locally to gain access to some local resource such as a database
3.
4.
To obtain credentials to move laterally or escalate privileges within the client's network
There are many tools available to us as penetration testers to assist with privilege escalation. Still, it is also essential to understand how to perform privilege escalation checks and leverage flaws manually to the extent possible in a given scenario. We may run into situations where a client places us on a managed workstation with no internet access, heavily firewalled, and USB ports disabled, so we cannot load any tools/helper scripts. In this instance, it would be crucial to have a firm grasp of Windows privilege escalation checks using both PowerShell and Windows command-line.
Windows systems present a vast attack surface. Just some of the ways that we can escalate privileges are:
Abusing Windows group privileges
Abusing Windows user privileges
Bypassing User Account Control
Abusing weak service/file permissions
Leveraging unpatched kernel exploits
Credential theft
Traffic Capture
and more.
[From mrb3n] Scenario 1 - Overcoming Network Restrictions
I once was given the task to escalate privileges on a client-provided system with no internet access and blocked USB ports. Due to network access control in place, I could not plug my attack machine directly into the user network to assist me. During the assessment, I had already found a network flaw in which the printer VLAN was configured to allow outbound communication over ports 80, 443, and 445. I used manual enumeration methods to find a permissions-related flaw that allowed me to escalate privileges and perform a manual memory dump of the LSASS process. From here, I was able to mount an SMB share hosted on my attack machine on the printer VLAN and exfil the LSASS DMP file. With this file in hand, I used Mimikatz offline to retrieve the NTLM password hash for a domain admin, which I could crack offline and use to access a domain controller from the client-provided system.
[From mrb3n] Scenario 2 - Pillaging Open Shares
During another assessment, I found myself in a pretty locked-down environment that was well monitored and without any obvious configuration flaws or vulnerable services/applications in use. I found a wide-open file share, allowing all users to list its contents and download files stored on it. This share was hosting backups of virtual machines in the environment. I was explicitly interested in virtual harddrive files (.VMDK and .VHDX files). I could access this share from a Windows VM, mount the .VHDX virtual hard drive as a local drive and browse the file system. From here, I retrieved the SYSTEM, SAM, and SECURITY registry hives, moved them to my Linux attack box, and extracted the local administrator password hash using the secretsdump.py tool. The organization happened to be using a gold image, and the local administrator hash could be used to gain admin access to nearly every Windows system via a pass-the-hash attack.
[From mrb3n] Scenario 3 - Hunting Credentials and Abusing Account Privileges
In this final scenario, I was placed in a rather locked-down network with the goal of accessing critical database servers. The client provided me a laptop with a standard domain user account, and I could load tools onto it. I eventually ran the Snaffler tool to hunt file shares for sensitive information. I came across some .sql files containing low-privileged database credentials to a database on one of their database servers. I used an MSSQL client locally to connect to the database using the database credentials, enable the xp_cmdshell stored procedure and gain local command execution. Using this access as a service account, I confirmed that I had the SeImpersonatePrivilege, which can be leveraged for local privilege escalation. I downloaded a custom compiled version of Juicy Potato to the host to assist with privilege escalation, and was able to add a local admin user. Adding a user was not ideal, but my attempts to obtain a beacon/reverse shell did not work. With this access, I was able to remote into the database host and gain complete control of one of the company's clients' databases.
Why does Privilege Escalation Happen?
There is no one reason why a company's host(s) may fall victim to privilege escalation, but several possible underlying causes exist. Some typical reasons that flaws are introduced and go unnoticed are personnel and budget. Many organizations simply do not have the personnel to properly keep up with patching, vulnerability management, periodic internal assessments (self-assessments), continuous monitoring, and larger, more resource-intensive initiatives. Such initiatives may include workstation and server upgrades, as well as file share audits (to lock down directories and secure/remove sensitive files such as scripts or configuration files containing credentials).
Useful Tools
There are many tools available to us to assist with enumerating Windows systems for common and obscure privilege escalation vectors. Below is a list of useful binaries and scripts, many of which we will cover within the coming module sections.
C# project for performing a wide variety of local privilege escalation checks
PowerShell script for finding common Windows privilege escalation vectors that rely on misconfigurations. It can also be used to exploit some of the issues found
C# version of PowerUp
PowerShell script for enumerating privilege escalation vectors written in PowerShell 2.0
SessionGopher is a PowerShell tool that finds and decrypts saved session information for remote access tools. It extracts PuTTY, WinSCP, SuperPuTTY, FileZilla, and RDP saved session information
Watson is a .NET tool designed to enumerate missing KBs and suggest exploits for Privilege Escalation vulnerabilities.
Tool used for retrieving passwords stored on a local machine from web browsers, chat tools, databases, Git, email, memory dumps, PHP, sysadmin tools, wireless network configurations, internal Windows password storage mechanisms, and more
WES-NG is a tool based on the output of Windows' systeminfo utility which provides the list of vulnerabilities the OS is vulnerable to, including any exploits for these vulnerabilities. Every Windows OS between Windows XP and Windows 10, including their Windows Server counterparts, is supported
We can also find pre-compiled binaries of Seatbelt and SharpUp here, and standalone binaries of LaZagne here. It is recommended that we always compile our tools from the source if using them in a client environment.
Depending on how we gain access to a system we may not have many directories that are writeable by our user to upload tools. It is always a safe bet to upload tools to C:\Windows\Temp because the BUILTIN\Users group has write access.
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