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What is Penetration Testing?

Penetration Testing, often abbreviated to PenTesting, is a method of testing the security of a system through attempting to discover and actively exploit vulnerabilities within the system. It is amongst the most effective methods of determining the actual risk posed by a system. This is due to the fact that the risk of present vulnerabilities is not estimated but they are exploited to determine how much leverage they would offer an attacker.

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PrivEsc: Insecure Service Permissions

I’ve written a few articles recently about methods of escalating privileges on Windows machines, such as through DLL Hijacking and Unquoted Service Paths, so here I’m continuing the series with Privilege Escalation through Insecure Service configurations. This one’s pretty simple issue really, generally speaking it’s simply a matter of altering the service so that it runs the executable and parameters you want it to, instead the default configuration allowing you to supply a command and privilege level for the execution. So you can simply run the add user command as local system and create your own local administrator account!

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PrivEsc: Unquoted Service Path

One method for escalating permission from Local/Domain User to Local Administrator, is "Unquoted Service paths". In my experience finding unquoted service paths is a common occurrence, however actually being able to exploit them is not. In this article we'll explore how to find these issues and how to quickly determine if they're exploitable or not.

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Calculating Subnets and CIDR Quickly

A friend of mine mentioned recently that he has to work out subnet masks in his head for an exam and commented in reality he’d just use a subnet calculator. Whilst this is probably true, there’s a quick trick that might help if you’re calculating subnets under duress. This isn’t a full write up and offers no real explanation of why it works, it’s just pointing out a trick you may have missed which might come in handy one day!

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Calculating the Details of Awkward Subnets

I posted recently about calculating subnets and CIDR notation quickly, but I didn’t mention in that post host to quickly get the Network ID, first host and Broadcast address for a subnet given an awkward address. This is another easy trick that covers that!

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Custom Rules for John the Ripper

Whilst Hashcat is often provable faster than John the Ripper, John is still my favourite. I find it simple to use, fast and the jumbo community patch (which I recommend highly) comes packed with hash types making it a versatile tool.

One of the features of these tools, which is often unknown or at least under appreciated is the ability to create custom “rules” for teaching the tool how to dynamically generate potential passwords. Since Microsoft implemented “Password Complexity” and this was enforced around the globe, user have made the jump from a password of: password, to the [sarcasm] much more secure [/sarcasm]: Password1.

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Linux PrivEsc: Abusing SUID

Recently during a CTF I found a few users were unfamiliar with abusing setuid on executable on Linux systems for the purposes of privilege escalation. If an executable file on Linux has the “suid” bit set when a user executes a file it will execute with the owners permission level and not the executors permission level. Meaning if you find a file with this bit set, which is owned by a user with a higher privilege level than yourself you may be able to steal their permissions set.

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Windows Desktop Breakout

Many organisations “lock-down” their desktop environments to reduce the impact that malicious staff members and compromised accounts can have on the overall domain security. Many desktop restrictions can slow down an attacker but it’s often possible to “break-out” of the restricted environment. Both assessing and securing these desktop environments can be tricky, so I’ll run you through how I assess them here, highlight some of the tricks and the methodology that I use with the intention that both breakers and defenders can get a better look at their options.

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PrivEsc: DLL Hijacking

I posted earlier about Privilege Escalation through Unquoted Service Paths and how it’s now rare to be able to exploit this in the real world due to the protected nature of the C:\Program Files and C:\Windows directories. It’s still possible to exploit this vulnerability, but only when the service executable is installed outside of these protect directories which in my experience is rare. Writing that post though got me thinking about another method of privilege escalation which I think is a little more common to see – DLL Hijacking.

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An Introduction to Penetration Testing AWS

When penetration testing Amazon Web Services (AWS) environments there are different perspectives the assessment could consider, some are very similar to external infrastructure/web application assessments and some are different.

I’ll separate the things that are the same from the things that are different to traditional penetration testing by considering the following types of cloud testing and then breaking each one down into the kinds of testing that could take place:

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Spoofing Packets and DNS Exfiltration

Following a successful penetration test, you may have large amounts of data to exfiltrate from an environment specifically hardened to make it difficult to exfiltrate data. For example, the network might have a firewall that explicitly blocks common exfiltration methods – such as SSH, HTTPS, HTTP.

It is common that you can still exfiltrate data from these networks by using DNS. For example you could make a request to a domain name that you control where the subdomain contains some information to be exfiltrated. Such as sensitive-data-here.attacker.example.com. DNS is a recursive system, such that if you send this request to a local DNS server, it will forward it on and on until it reaches the authoritative server. If you control the authoritative server, you can simply read the sensitive data from the DNS logs.

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An Introduction to PenTesting Azure

I recently wrote an introduction to PenTesting an AWS Environment. A sensible place to start given that I included that in Q1 of 2018 Amazon holds a 33% market share in cloud whereas Microsoft only holds 13%. However I did want to add a few notes that are specific to PenTesting within Azure environments here.

Many of the concepts are the same however, in my AWS article I broke the perspective a penetration tester could take of a cloud environment down into testing “on the cloud”, “in the cloud”, and “testing the cloud console.” That concept remains the same, which is:

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Preventing Windows Accounts Being Bruteforced

In a previous article we discussed how bruteforcing Windows accounts is often easier than people expect. In this post - we'll cover some steps to harden these accounts.

The Observation Window

When configuring an account lockout threshold on a Domain another setting is suggested, the observation window. This setting effectively reduces the protection of the account lockout by setting a timer. For example, a lockout threshold of 5 and an observation window of 30 minutes has the impact of meaning that if an attacker attempts 5 incorrect passwords within 30 minutes the account will lock - but four passwords would not cause it to lock.

Therefore, an attacker could attempt 4 passwords every 30 minutes - or 192 per account per day, without locking any accounts.

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Fixing LLMNR and NetBIOS-NS Spoofing

In our article LLMNR and NetBIOS-NS Spoofing with Responder we stepped you through how to exploit a very common issue on Windows networks. In this one, we’re going to cover how to fix it.

Link-Local Multicast Name Resolution (LLMNR) and NetBIOS-Name Service (NBT-NS) are name resolution protocols that are enabled by default on Windows machines. They’re both used as a fallback for DNS. If a machine requests a hostname, such as when attempting to connect to a file-share, and the DNS server doesn’t have an answer – either because the DNS server is temporarily unavailable or the hostname was incorrectly typed – then an LLMNR request will be sent, followed by an NBT request. LLMNR is a multicast protocol and NBT-NS is a broadcast protocol.

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Extracting Domain Hashes: VSSAdmin

We covered extracting domain hashes with Mimikatz previously, but that's not always the best approach - for example where anti-virus is getting in the way. However there are other options for the same goal. This time around we'll take a look at using Vssadmin, a built-in Windows tool. VSSAdmin is the Volume Shadow Copy Administrative  command-line tool and it can be used to take a copy of the NTDS.dit file - the file that contains the active directory domain hashes.

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Becoming a Penetration Tester

Breaking into Penetration Testing can be a daunting career move; so in this article we talked about ways you can make your first move towards a career in this industry. To be clear, this isn't a definitive guide to the industry - it's just our opinion on what has worked for our team and what we like to look for when hiring. So, when interviewing for a position as a junior penetration tester - what makes you stand out from the crowd?

Whilst it's certainly useful to know how to use common security testing tools, it's better if you can understand what's going on under the hood. It's also just as important to know how to remediate the issues found. For example, knowing which flags to use when executing Responder is good; but it's better if you can talk about the underlying protocols such as Link Local Multicast Name Resolution and why it can lead to significant vulnerabilities.

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LLMNR and NetBIOS-NS Spoofing with Responder

Link-Local Multicast Name Resolution (LLMNR) and NetBIOS-Name Service (NBT-NS) are name resolution protocols that are enabled by default on Windows machines. They’re both used as a fallback for DNS. If a machine requests a hostname, such as when attempting to connect to a file-share, and the DNS server doesn’t have an answer – either because the DNS server is temporarily unavailable or the hostname was incorrectly typed – then an LLMNR request will be sent, followed by an NBT request. LLMNR is a multicast protocol and NBT-NS is a broadcast protocol.

Therefore, an attack can take place where an attacker responds to these requests with illegitimate requests. For example, directing the requesting user to connect to the attacker's machine where an authentication attempt will be made – disclosing hashed credentials for the targeted user.

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PrivEsc: Extracting Passwords with Mimikatz

We recently published an article on using Incognito for privilege escalation as part of a short series on using Metasploit. In this article we’ll cover an alternative approach for privilege escalation – extracting plaintext credentials. Whilst incognito is generally easier to use, Mimikatz is powerful and flexible.

In this part we’re just going to look at password extraction; but Mimikatz can be used for many other attacks – such as extracting domain hashes from a domain controller. As before, password extraction is really a post-exploitation steps and is very useful for escalating from local administrator access to domain administrator access. As this is a post-exploitation step, we’ll be starting with a SYSTEM shell through PsExec for this demonstration. As an example of when these steps could be deployed, they could be a step taken after successfully performing an attack to gain an initial foothold such as LLMNR and NBT-NS Spoofing, which we covered previously.

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PrivEsc: Token Impersonation with Incognito

Incognito is a tool which can be used for privilege escalation, typically from Local Administrator to Domain Administrator. It achieves this by allowing for token impersonation. As a local administrator can read the entirety of memory, if a domain administrator is logged in their authentication token can be stolen. We'll investigate its use here.

There are several types of authentication token on Windows systems, but Delegation tokens can be used network wide. This therefore allows an attacker to extract one of these tokens and then execute commands on other machines (such as the Domain Controller). Incognito can be executed within Meterpreter, or as a standalone EXE.

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Using Metasploit

Metasploit is an exploitation framework. It’s a core tool of the penetration tester’s toolset and we use it for several of our vulnerability demonstrations, so it makes sense to write a quick “introduction to” for Metasploit. We’re going to look at the module system, navigating around, setting variables and running payloads.

Since there are so many modules, it's worthwhile becoming familiar with the search functionality. You can search for modules using the "search" command, and you can filter results based on features such as module type, CVE number, or platform. The command "help search" will reveal all filter options.

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Network Mapping with Nmap

Before being able to determine if systems are vulnerable, it’s critical to first find as many active systems within the scope as possible and to accurately determine what services those systems expose. A common tool for use in network mapping is Nmap.

Before we start looking at the many, many, options that Nmap has, we'll take a look at a simple example. Nmap can be invoked with a target IP address and it will perform a default scan. If Nmap is invoked with administrative/root privileges it will perform a "half-open" SYN scan which is beneficial for its potential to be stealthier and faster than a "full" scan. A full-handshake scan can will be performed if administrative permissions are not granted, or optionally with the -sT flag.

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ASREP Roasting

If an Active Directory user has pre-authentication disabled, a vulnerability is exposed which can allow an attacker to perform an offline bruteforce attack against that user’s password.

This attack is commonly known as “AS-REP Roasting” in reference to Authentication Service Requests, a part of the process of authentication with Kerberos. An attacker who is able to find a user with pre-authentication disabled can request an AS-REP ticket for that user and this will contain data encrypted with the user’s password.

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Bruteforcing Kerberos

It is possible to brute-force Windows accounts directly, using tools like Metasploit using modules such as smb_login, which will target port 445 (SMB). However, it’s also possible to brute-force the Active Director authentication protocol Kerberos directly.

This can be beneficial to an attack for two reasons, the first is that it will be logged differently and depending on how the blue team are monitoring for attacks it might fly under the radar. A standard login attempt that fails will result in event 4625, whereas a failed Kerberos login attempt will likely result in event 4771.

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Kerberoasting

Any domain user within Active Directory can request a service ticket (TGS) for any service that has an SPN (Service Principal Name). A part of the service ticket will be encrypted with the NTLM hash of the target user, allowing for an offline bruteforce attack.

This is true for user accounts and computer accounts, but computer account passwords are randomised by default and rotated frequently (every 30 days). However service user accounts may have weak passwords set which could be cracked. This attack is commonly called Kerberoasting. Although, don’t confuse this attack with the similarly named ASREP Roasting. A common setup where you might find this vulnerability is where a service account has been set up for Microsoft SQL Server.

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An Introduction to IPv6

IPv6 is not new, RFC1883 discussed the protocol back in 1995. However, it has been updated several times, becoming a Draft Standard with RFC2460 in 1998, and an Internet Standard with RFC8200 in 2017!

If you’re wondering if there was an IPv5 the answer is sort of, in the Experimental Internet Stream Protocol, Version 2 (ST-II) which used the IP version number 5 within its packet header, that’s RFC1190. IPv7 was sort of RFC1475, IPv8 was sort of RFC1162, and for an April fools joke we go IPv9 in RFC1606.

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Bruteforcing Windows Accounts

A common configuration on Windows Active Directory accounts is to have an account lockout threshold of say, 5 invalid attempts, and an observation window of 30 minutes. This is likely due to the fact that the “Suggested Setting” after setting a threshold is to enable a short observation window.

When setting an account lockout threshold, Windows “suggests” that you set the observation window at the same time, to 30 minutes. The observation window is often overlooked as a security risk; however it allows an attacker to perform a bruteforce attack without locking an account.

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Hashcracking with AWS

Password cracking is a common step during compromising networks, from cracking wireless networks to compromising user passwords captured when LLMNR spoofing. In a previous post, I showed the steps to capture a WPA handshake and crack it using Hashcat. On my tiny travel laptop I achieved 416 hashes per second, which is…slow. AWS offers “GPU Optimized” EC2 instances which can offer a significant speed increase. 

In this post we'll run through setting up Hashcat on an AWS instance to allow for rapid password cracking. These instances are pricey, but you often only need to run them for short bursts.

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Extracting Domain Hashes: Mimikatz

We previously covered how to perform incredibly fast hashcracking with AWS. In this post we’ll take a step back, and look at one simple method to extract the hashes from a domain controller. To be clear, this is a post exploitation step and to perform these steps a domain administrator account will be needed.

There are several tools which can be used to extract hashes directly on a domain controller, such as fgdump or Meteterpreter’s hashdump too. However, Mimikatz can perform this step from any domain joined machine, which is a little easier and often a benefit when it comes to antivirus evasion steps.

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