How I Use Firefox as a Web App Pentesting Browser

April 3rd, 2016 by Patrick Thomas

I’m spending more of my time these days helping other people be effective at security testing applications, and as part of that I’m a huge fan of “over the shoulder” mentoring. Some of the most useful things that I’ve learned from others are not things they thought to mention, but rather those moments of “hey, back up a second — what was that thing you just did?“. Sometimes it’s commands or small utility tools, shortcut keys or capabilities of a program I didn’t know about, or just some quick and dirty technique that someone uses all the time but doesn’t think is special enough to talk about.

To that end, here’s a quick walkthrough of the broad strokes of how I set up Firefox for use in testing. My preferred testing setup is Firefox through Burp: the simplest setup is going to be useful, but there are a lot of small configuration details that can help a stock Firefox become even more of a pentesting asset.

Use Profiles

To test authentication and authorization issues you’re really going to need two browsers open at the same time, in different principal contexts (such “User”/”Admin”, “Tenant1″/”Tenant2”, and the ever populated “Unauthenticated”). Then, when you notice something that might have horizontal or vertical privilege issues, you can simple paste the request into the other browser, or swap cookies between your two active browsers. I prefer to run both through the same Burp instance so that I can easily diff or replay between equivalent requests/responses for different principals.

That’s where profiles come in. Normally when you launch Firefox it’ll give you multiple windows that share a common profile; however, if you launch with special command line flags, you can run two completely separate profiles at the same time. To create and manage profiles, launch Firefox Profile manager by adding the Profile Manager flag:

firefox -no-remote -ProfileManager

After creating different profiles, you can create shortcuts to launch them directly, eg:

"C:\path\to\firefox.exe" -no-remote -profile "C:\path\to\Mozilla\Firefox\Profiles\Assess1"
"C:\path\to\firefox.exe" -no-remote -profile "C:\path\to\Mozilla\Firefox\Profiles\Assess2"

To keep track of which is which, both visually and in Burp, I add a contrasting color themes (such as blue and red) and use a plugin to ensure that each sends an identifying header (see plugins section).

firefox testing config

As a sidenote to auth testing, I’m really excited about the AuthMatrix Burp Plugin. I haven’t gotten to properly put it through its paces yet, but more info to come when I have an informed opinion.

Plugins

Firefox Add-On collection that includes a lot of tools mentioned below and that you may find useful during a penetration test.

Some specific plugins you’ll definitely want:

And a couple other pieces of functionality which can be filled by various plugins:

  • Manage proxy settings:
    • FoxyProxy
    • ProxySelector
  • Change User Agents
    • UserAgentSwitcher
  • Simplify JS and JSON
    • JSONView
    • Javascript Deminifier
  • Passively detect remote technologies:
    • Wappalyzer
  • Fetch lots of content at once:
    • DownThemAll!
  • Interact with REST services:
  • RESTClient (although Chrome’s Postman is better, SoapUI is quite serviceable, and Burp will also work)

For Foxyproxy, I like to just blacklist a bunch of domains right in the browser so that they’ll never get passed to the proxy. This keeps the Burp request history cleaner and means I don’t have to make too many assumptions in Burp about what hosts an application will talk to (It also means you won’t have to reconfigure Firefox for each engagement to keep it clean). If the browser is too chatty through Burp you risk losing some valuable information when you rely on “Show only in-scope items”.
foxyproxy blacklist

 

When advertising and tracking domains are out of scope, you can also load large lists of advertisers and blacklist those from your proxy to keep the burp state even trimmer.

I use the ModifyHeaders plugin to send a unique header from each browser profile (eg, “BrowserProfile: AssessRed”). This helps me keep track in Burp during my testing, and it can also seriously help with potential client issues when they can easily identify and (hopefully) rule out your traffic as a potential cause of a problem.

Disable Chatty Features

Speaking of chatty features, you’ll probably want to disable a bunch of automatic/implicit traffic that could bloat your Burp state or create red herrings in testing: https://support.mozilla.org/en-US/kb/how-stop-firefox-making-automatic-connections

You’ll also want to tweak some settings in about:config to prevent both chatty traffic and sending potentially sensitive client URLs to public antimalware lists:

browser.safebrowsing.enabled -> false
browser.safebrowsing.malware.enabled -> false

A Few Words on Chrome

You can do a lot of this with Chrome. It supports profiles, has many approximately equivalent plugins, and can be configured to not use the system proxy by installing proxy manager plugins. That said, it feels like you have to work harder to make Chrome play nice in a pentesting environment. YMMV.

Burp Testing Profile

Although it’s not related to Firefox, one thing that I notice biting a lot of people is that they don’t load a consistent profile. Every single new test I do starts with a standard, clean burp state file with all of my preferences loaded in it. I just copy “InitialEngagementBurpState.burp” into my notes directory, load it in, and know that I’m getting all my standard preferences such as autosave (every hour (!) and into a directory that I can regularly clean up), logging, plugin config, etc. I’ve seen colleagues forget this on back to back tests and lose their first day of testing each time because they didn’t manually enable the autosave and hit a crash. (Update Sept 2016: this is less relevant now with Burp’s new project file feature. I’m still figuring out if there are any gotchas in it, but it really helps persisting defaults and making it harder to be dumb.)

What about you?

What did I miss? Some favorite plugin, or special approach? What’s unique about your own setup that you take some pride in?

 

BlackHat USA Multipath TCP Tool Release & Audience Challenge

August 6th, 2014 by Patrick Thomas

(Crossposting & backdating some content from the Neohapsis blog, which will soon be defunct)

We hope everyone found something interesting in our talk today on Multipath TCP. We’ve posted the tools and documents mentioned in the talk at:

https://github.com/Neohapsis/mptcp-abuse

Update (Aug 12, 2014): We’ve now also added the slides from the talk.


At the end we invited participants to explore MPTCP in a little more depth via a PCAP challenge.

Without further ado, here’s the PCAP: neohapsis_mptcp_challenge.pcapng

It’s a simple scenario: one MPTCP-capable machine sending data to another. The challenge is “simply” to reassemble and recover the original data. The data itself is not complex so you should be able to tell if you’re on the right track, but getting it exactly right will require some understanding of how MPTCP works.

If you think you have it, tweet us and follow us (@secvalve and @coffeetocode) and we’ll PM you to check your solution. You can also ask for questions/clarifications on twitter; use #BHMPTCP so others can follow along. Winner snags a $100 Amazon gift card!

Hints #0:

  • The latest version of Wireshark supports decoding mptcp options (see “tcp.options.mptcp”).
  • The scapy version in the git repo is based on Nicolas Maitre’s and supports decoding mptcp options. It will help although you don’t strictly need it.
  • The is an mptcp option field to tell the receiver how a tcp packet fits into the overall logical mptcp data flow (what it is and how it works is an exercise for the user🙂 )
  • It’s possible to get close with techniques that don’t fully understand MPTCP (you’ll know you’re close). However the full solution should match exactly (we’ll use md5sum)

Depending on how people do and questions we get, we’ll update here with a few more hints tonight or tomorrow. Once we’ve got a winner, we’ll post the solution and code examples.

Update: Winners and Solution

We have some winners! Late last night @cozinuzo contacted us with a correct answer, and early this morning @darkfiberiru got it too.

The challenge was created using our fragmenter PoC tool, pushing to a netcat opened socket on an MPTCP-aware destination host:

python mptcp_fragmenter.py -n 9 --file=MPTCP.jpg --first_src_port 46548 -p 3000 192.168.1.33

The key to this exercise was to look at the mechanism that MPTCP uses to tell how a particular packet fits into the overall data flow. You can see that field in Wireshark as tcp.options.mptcp.dataseqno, or in mptcp-capable scapy as packet[TCPOption_MP].mptcp.dsn.

mptcp_wireshark_column

 

 

The mptcp-capable scapy in our mptcp-abuse git repo can easily do the reassembly across all the streams using this field.

Here’s the code (or as a Gist):

# Uses Nicolas Maitre's MPTCP-capable scapy impl, so that should be
# on the python path, or run this from a directory containing that "scapy" dir
from scapy.all import *

packets = rdpcap("pcaps/neohapsis_mptcp_challenge.pcap")
payload_packets = [p for p in packets if TCP in p
                   and p[IP].src in ("192.168.1.26", "192.168.1.33")
                   and TCPOption_MP in p
                   and p[TCPOption_MP].mptcp.subtype == 2
                   and Raw in p]

f = open("out.jpg", "w")

for p in sorted(payload_packets, key=lambda p: p[TCPOption_MP].mptcp.dsn):
 f.write(p.load)
f.close()

These reassemble to create this image:

 

mptcp

 

 

The md5sum for the image is 4aacab314ee1a7dc5d73a030067ae0f0, so you’ll know you’ve correctly put the stream back together if your file matches that.

Thanks to everyone who took a crack at it, discussed, and asked questions!

What Kickstarter Did Right

February 17th, 2014 by Patrick Thomas

Only a few details have emerged about the recent breach at Kickstarter, but it appears that this one will be a case study in doing things right both before and after the breach.

What Kickstarter has done right:

  • Timely notification
  • Clear messaging
  • Limited sensitive data retention
  • Proper password handling

Timely notification

The hours and days after a breach is discovered are incredibly hectic, and there will be powerful voices both attempting to delay public announcement and attempting to rush it. When users’ information may be at risk beyond the immediate breach, organizations should strive to make an announcement as soon as it will do more good than harm. An initial public announcement doesn’t have to have all the answers, it just needs to be able to give users an idea of how they are affected, and what they can do about it. While it may be tempting to wait for full details, an organization that shows transparency in the early stages of a developing story is going to have more credibility as it goes on.

Clear messaging

Kickstarter explained in clear terms what was and was not affected, and gave straightforward actions for users to follow as a result. The logging and access control groundwork for making these strong, clear statements at the time of a breach needs to be laid far in advance and thoroughly tested. Live penetration testing exercises with detailed post mortems can help companies decide if their systems will be able to capture this critical data.

Limited sensitive data retention

One of the first questions in any breach is “what did they get?”, and data handling policies in place before a breach are going to have a huge impact on the answer. Thinking far in advance about how we would like to be able to answer that question can be a driver for getting those policies in place. Kickstarter reported that they do not store full credit card numbers, a choice that is certainly saving them some headaches right now. Not all businesses have quite that luxury, but thinking in general about how to reduce the retention of sensitive data that’s not actively used can reduce costs in protecting it and chances of exposure over the long term.

Proper password handling (mostly)

Kickstarter appears to have done a pretty good job in handling user passwords, though not perfect. Password reuse across different websites continues to be one of the most significant threats to users, and a breach like this can often lead to ripple effects against users if attackers are able to obtain account passwords.

In order to protect against this, user passwords should always be stored in a hashed form, a representation that allows a server to verify that a correct password has been provided without ever actually storing the plaintext password. Kickstarter reported that their “passwords were uniquely salted and digested with SHA-1 multiple times. More recent passwords are hashed with bcrypt.” When reading breach reports, the level of detail shared by the organization is often telling and these details show that Kickstarter did their homework beforehand.

A strong password hashing scheme must protect against the two main approaches that attackers can use: hash cracking, and rainbow tables. The details of these approaches have been well-covered elsewhere, so we can focus on what Kickstarter used to make their users’ hashes more resistant to these attacks.

To resist hash cracking, defenders want to massively increase the amount of work an attacker has to do to check each possible password. The problem with hash algorithms like SHA1 and MD5 is that they are too efficient; they were designed to be completed in as few CPU cycles as possible. We want the opposite from a password hash function, so that it is reasonable to check a few possible passwords in normal use but computationally ridiculous to try out large numbers of possible passwords during cracking. Kickstarter indicated that they used “multiple” iterations of the SHA1 hash, which multiplies the attacker effort required for each guess (so 5 iterations of hashing means 5 times more effort). Ideally we like to see a hashing attempt take at least 100 ms, which is a trivial delay during a legitimate login but makes large scale hash cracking essentially infeasible. Unfortunately, SHA1 is so efficient that it would take more than 100,000 iterations to raise the effort to that level. While Kickstarter probably didn’t get to that level (it’s safe to assume they would have said so if they did), their use of multiple iterations of SHA1 is an improvement over many practices we see.

To resist rainbow tables, it is important to use a long, random, unique salt for each password. Salting passwords removes the ability of attackers to simply look up hashes in a precomputed rainbow tables. Using a random, unique salt on each password also means that an attacker has to perform cracking on each password individually; even if two users have an identical password, it would be impossible to tell from the hashes. There’s no word yet on the length of the salt, but Kickstarter appears to have gotten the random and unique parts right.

Finally, Kickstarter’s move to bcrypt for more recent passwords is particularly encouraging. Bcrypt is a modern key derivation function specifically designed for storing password representations. It builds in the idea of strong unique salts and a scalable work factor, so that defenders can easily dial up the amount computation required to try out a hash as computers get faster. Bcrypt and similar functions such as PBKDF2 and the newer scrypt (which adds memory requirements) are purpose built make it easy to get password handling right; they should be the go-to approach for all new development, and a high-priority change for any codebases still using MD5 or SHA1.