What’s the go-to phishing technique or exploit?December 17, 2014
This blog post is inspired by a question sent to a local mailing list. The original poster asks, what’s the go-to phishing technique or exploit in a blackbox situation? Here’s my response:
I’ve had to do this before, I sell tools to do it now, and I’ve seen how others teach and go about this particular process. First, I recommend that you read MetaPhish. No other paper or talk has influenced how I think about this process more:
You’ll notice I said the word process. Before you dig into a toolset, you’ll want to figure out the process you’re going to use. Here’s what I used and it has parallels with the processes I see others use now [regardless of toolset]:
0. Information Gathering
Find out about your target, harvest email addresses, etc. etc. etc.
This is the phase where you sample the target’s client-side attack surface. I used to send a few fake LinkedIn invitations across an org and direct those folks to a web app that profiles their browser. Similar information to what you see here: http://browserspy.dk/
2. Stand up a Test Environment
Next, I recommend that you create a virtual machine to mirror their environment as closely as possible. Install patches and other tweaks you think may be present. This isn’t the place to underestimate their posture. I’d also recommend trying out the different A/V products you expect to see at this point. Use the information from the reconnaissance step to make this as exact as possible.
3. Choose your attack
Now, you will need to select an attack to use against your target. I really recommend that you stay away from the memory corruption exploits in the Metasploit Framework. You can tweak them to get around some anti-virus products. But, you really need to pay attention to the exploit’s needs. For example, let’s say the target profile reveals a vulnerable version of IE and Metasploit has an exploit for it. What are the dependencies of that exploit? Does it also require Java 1.6 to help it get past some of Windows’ protections? You could play this game. Or, you could skip it altogether.
Many folks who execute these kinds of engagements regularly use user-driven attacks. A user-driven attack is an attack that relies on functionality and fooling the user into taking some detrimental action. The Java Applet attack is an example of a very popular user-driven attack. I’m surprised it still works today, but *shrug*. Embedding a macro into a Word or Excel spreadsheet is also effective.
4. Pair your attack with a payload
Don’t take it for granted that you’ll walk out of your target’s network with a Metasploit Framework payload. I see egress as one of the toughest problems when working with a harder target. If you have to use a Metasploit Framework payload, windows/meterpreter/reverse_https is your best bet here. I recommend that you look for and consider other options though. A lot of organizations who do this kind of work have a custom payload or they buy one. If I were in a hurry to cobble up a process and didn’t have a budget, I’d look at building something in PowerShell. The main things you care about:
a. Is the payload proxy aware? Will it take the same actions that the user’s browser would take to get out to the internet?
b. Can I match the payload’s characteristics to the target environment? For example, making its User-Agent match something legitimate?
bb. If I opt to go SSL, can I use a legitimate certificate? If not, does the payload at least try to look like legitimate traffic if I communicate without SSL?
c. Is the payload asynchronous? You really want something reliable that doesn’t stand out while you figure out what to do next on your target’s network.
d. Can I pair this payload with my attack? This is an important consideration. If you have a great piece of custom malware but *can’t* pair it with your chosen attack, it’s not useful to you for this phase of your engagement.
Your custom payload [bought/built] does not need to be fully functional. Its main goal is to defeat egress restrictions and act as a lifeline while you figure out the best steps to fortify your access [if that’s what your customer wants]. The main thing it needs to be able to do is spawn another payload.
Here’s one of my favorite talks on how to pull something like this together, quickly:
I also recommend that you setup infrastructure for each piece of this attack. You should send phishes from different places. You should host your recon app on its own server. The server your user-driven stages your payload from should differ from the server the payload actually communicates with [if your payload is delivered in stages]. Ideally, your asynchronous lifeline payload should call home to multiple hosts in case one of them becomes blocked.
5. Deliver the package
The final phase is to send the package on to your target. I don’t recommend that you spray every email you found. If your goal is to demonstrate a targeted attack, be targeted.
Personally, I’m a stickler for pixel perfect phishing emails and I’m not a fan of crafting an HTML email in a hacker tool to achieve this. If in doubt, I recommend that you use the same email client that your legend [the person you’re pretending to be] would use to send the email. If your target is someone in HR and your legend is someone applying for a job, use Gmail to send your phish. Preferably, the same Gmail account noted in the resume.doc you embedded a macro inside of.
Before you phish, I recommend that you send your package to yourself, through infrastructure that mirrors your target environment as closely as possible. If your target uses a cloud email service, try to get an account on the free or low-tier paid version of this service and send your package to yourself there. If your target uses a more traditional Exchange+Outlook setup, see if you can build a lab with those pieces or rely on a friend who has access to something similar. The main point here is to make sure your lovingly crafted bundle of good isn’t going to the spam folder. It’d be a shame to go through all of this work to get stopped by that.
Even if you have a favorite “go to” user-driven attack, I recommend executing this process anyways. You don’t want to fire an attack package crafted for a Windows environment only to find that your target is a MacOS X shop.