Defcon 20-zulla-improving-web-vulnerability-scanning

Improving Web Vulnerability Scanning 1

Daniel Zulla

Introduction
Hey! 2

■ Hi there!
■ I’m Dan. This is my ﬁrst year at DEFCON.
■ I do programming and security start-ups.
■ I do some penetration testing as well

More Introduction 3

■ Today I’m going to talk about vulnerability scanning
■ Primary on the web
■ “The cloud” is involved as well
■ Network security too
■ I’ll show some things, so there is plenty of demo time
■ Have fun, thanks for being here!

Some Facts 4

■ There are a lot of web vulnerability scanners, fuzzers and penetration
testing tools out there already

■ Some of them work, some of them do not
■ But basically all of them have one thing in common:
They actually don’t attack web applications on the application layer

■ They mostly fuzz HTTP and sometimes perform injection attacks

Some more facts 5

■ The fundamental design of web scanners has not changed in over a
decade

■ But: The web has changed.
■ So there seems to be a problem.

Software Architecture
What web vulnerability scanners and fuzzers look like 6

Plugins
A HTTP Library

RXSS BSQLI EVAL
The Core

PXSS LFI OSC
Multithreading /
Output Engine
Forking
SQL RFI [...]

A pentesters point of view 7

■ Javascript/Ajax rich applications are still not
supported

■ Authenticated scanning is still incredibly
challenging / not reliable

■ Exploitation techniques are mostly poor

■ “I don’t know which scanner will work for
foo.com and which one for bar.com, so I
use toolchains”

A developers point of view 8

■ HTTP Libraries don’t support JS -
■ Javascript/Ajax rich applications are still not Scanners are based on an HTTP
supported Libraries

■ Authenticated scanning is still incredibly ■ Web Logins are not standarized -
challenging / not reliable So how should they be detected

■ Exploitation techniques are mostly poor ■ No time for exploits
(Already spent 100000 lines [and nights] of code
making the crawler immune to encoding issues,
■ “I don’t know which scanner will work for malformed HTML, redirects and binary content!)

foo.com and which one for bar.com, so I
use toolchains”
■ A false positive is better than a
false negative

How I see it 9

■ Both of them are right.

■ The web is a mess. Nobody cares about RFCs anymore. (Especially these SEO guys!)

■ 10 years ago, you would have expected a Query String at the end of a URL like
https://foo.com/xxx/yyy?foo=bar

■ Nowadays, https://foo.com/something.ext/foo/bar is good practice

■ The result: It’s incredibly hard for scanner developers to ﬁgure out the dynamic components
of an HTTP request. Because of that, we feel overhelmed and fuzz nearly everything.

■ Header Keys, Header Values, VHost, Cookie, Method, Path, Version, ...

How I see it 10

■ Fuzzing HTTP is incredibly important. You never know if you are talking to an apache2, nginx
or some hidden application server upstream

■ But it has nothing to-do with web vulnerability scanning

■ So - developers are struggling with websites because they use HTTP to crawl and attack
them. Things like ﬂash, images, javascript seems to be an unsolveable problem

■ Redirects are hard to handle sometimes (wait there is more)

■ Javascript redirects (after 10 seconds!) and of course: onmouseover, onclick, onfocus, ...

■ Flash isn’t helpful either

Web 2.0 11

■ But - WE DO SECURITY

■ Is it really our job to make sure that our software executed all the JS and grabbed all the
links?

■ When we spend 100 hours on the crawler, and 5 hours on the actual payloads (that’s how it
looks right now) something, somewhere, went terribly wrong

■ So - Is there a (open source?) piece of software that we could use instead of the HTTP
library? Something that has prooven its mastery in handling unpredictably broken web
content already? There is.

Webkit knows 13

■ Javascript ■ CSS Rendering

■ Javascript events ■ Binary Downloads

■ Redirects ■ Broken HTML

■ Flash ■ Broken CSS

■ Images ■ Performance

■ Websockets ■ Forking / Multiprocessing

■ WebGL ■ [...]

Software Architecture
What it should look like 14

The Front-End

A HTTP RXSS BSQLI EVAL
The Core
Library
PXSS LFI OSC

Reporting Engine SQL RFI [...]

The Exploitation Engine

Changes? Improvments? 15

■ Replacing the HTTP library by a Webkit Engine
■ Less code (A lot less code)
■ 100% support for JS/Ajax/Broken HTML/JS Events/Crazy Redirects
and all kinds of things

■ The ability to simulate human user behaviour
■ CSS Renderings (Two text ﬁelds beside each other: 10px - one of
them is a input[type=password]) - May be a login!

Making it scale (heavily) 16

■ Webkit is slow (Website rendering, Executing JS, ... - compared to -
Speaking Plaintext HTTP)

■ Downloading Images is slow
■ Waiting for delayed JS events is slow
■ Flash is even slower

Making it scale (heavily)
Bad news: Qt / PyQt / PySide 17

■ QtWebkit does not support multithreading
■ It tends to SEGFAULT from time to time :(
■ Multiple QApplication instances are almost impossible to handle in
one Python namespace

Making it scale (heavily)
Good news: Building a preforking TCP Server 18

■ Spawning a pool of processes works quite well (one QApplication
+one Browser instance per Process)

■ Simultaneous downloads
■ Better accessibility inside the scanner (multiprocessing insides loops
to increase performance)

Missing pieces 19

■ Mastering Authentication
■ Exploitation & Privilege Escalation
■ Geographically distributed scanning: Using the cloud
■ Reporting

Mastering Authentication 20

■ There is no such thing as a standarized web login
■ Basically, everybody develops access control on the web slightly
differently

■ You can try to detect them by the name/id of the attributes, but that is
not reliable

■ But in the end, Web logins generally have a few things in common
that makes them easily detectable. At least, for our browser engine

Mastering Authentication
Not more than 2 visible (!) text ﬁelds 21

has_login_texts()

Man-Behind-You Protection 22

is_input_hidden()

Geometry! Usually, the two visible text ﬁelds are under(), next_to() or at least
near(radius=10px) each other 23

X1 = X2
X1 = X2
!

Y1 = Y2

Mastering Authentication 24

■ That was easy!
■ The common way to solve that problem, is to iterate through a
wordlist (login, auth, signin, [...]) while checking the input[id],
input[name] attributes

■ That’s not necessarily wrong or bad practice
■ After putting the pieces together:
■ .login(“username”, “password”)

Demo Time 25

■ Proof Of Concept 1: Twitter (Some Javascript)
■ Proof Of Concept 2: Facebook (More Javascript)
■ Proof Of Concept 3: Google Plus (Most Javascript + Browser Hacks)

When we are signed in 26

■ New problems occur: How can we let the scanner check if we are
indeed signed in?

■ Common practive: Looking for a /logout/i String
■ The problem: Inefﬁcient. Likely to cause false positives
■ There has to be a better way:
■ Introduction “Strategies”

Strategy.Authentication
Step 1: Identiﬁcation 27

■ Identifying a login form (3-way approach, input[type=password],
geometry, [...])

Step 2: Error messages (Why a browser engines rocks) 28

■ Verifying wrong credentials - Random strings - Failed login

#BA.... -> #E4...

Step 3: Going in: .login(“..”, “..”) 29

■ Verifying valid credentials - Behaviour should not be similiar to the
behaviour of a invalid login

Step 4: Going out. .logout() 30

■ Doing similiar work again for .logout() function seems obsolote
■ But it really isn’t.
■ It is the basis to a .is_still_loggedin() function
■ Which is really important to stay logged in during crawling
■ And if the scanner logged itself out, it can simply .login() again
■ That’s cool. :-)

Exploitation and Privilege Escalation 31

■ There is a whole universe besides injection vulnerabilities
■ Usually, scanners don’t detect them
■ But they should
■ And now they can: .login(“user1”, “...”); .logout(); .login(“user2”, “...”)
■ => Demo Time: Privilege Escalation, Multi-User Systems

Geographically distributed scanning:
Using the cloud 32

■ When (injection) vulnerabilities are getting complicated:
■ Scenario 1: The backend of a website creates a log entry for every
new IP address. It logs the USERAGENT. The log entries are kept in a
SQL database. The function that creates the log entries, is vulnerable.
The User-Agent is injectable. The problem is:

■ It only works once. As soon as the IP is in the database, the function
won’t be executed anymore :-(

■ ==> SQLMap (and every other tool) will fail.

Using the cloud 33

■ But they shouldn’t!
■ The limitation is totally detectable
■ And a new IP is just as far away as a single EC2 API call

Using the cloud 34

■ Indeed! The cloud is a good thing for security :)
■ Demo Time: Introducing:
sqlmap and w3af (on steroids)

Combining “Strategies” and the
distributed scanning 35

■ Introducing next generation vulnerability scanning
■ Exploiting a really amazingly hard SQL Injection

■ Demo Time

Further Research & Additional Ideas 36

■ Country speciﬁc restrictions can be by-passed in a fully automatic
manner

■ (Error) messages can be parsed and interpreted: Wolfram Alpha
■ Bloomﬁlters should be integrated
■ Other “Strategies” should be implemented (the limitations are gone)

More Live Demos 37

■ Demonstrating a logical layer beyond Authentication:
.pay(“0000111122223333”, CVV=121, type=VISA)
.search(“search query”)
.sort(“DESC UNION SELECT [...]”)

■ Interpreting error messages
■ Pivoting on penetrated hosts - Spawning another scanner instance
■ And ﬁnally: Reporting!

Defcon 20-zulla-improving-web-vulnerability-scanning

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