Insinuator


Some outright rants from a bunch of infosec practitioners.

Archive for February 2012

On Friday we released our latest technical newsletter with the fancy title “Sell Your Own Device – A Field Study on Decommissioning of Mobile Devices”. It is the result of a field study on decommissioned mobile business devices bought on eBay and about how stored data may be extracted in different ways.

As always we love to share plenty of practical advise: At the end of the newsletter you will find the mitigating controls to securely handle mobile devices at the end of their life cycle process.

Find the newsletter here.
And a digitally signed version here.

Special thanks go to Sergej Schmidt for performing the field study.

Talking about our great team: Meet the whole ERNW crew at TROOPERS12, or even better: Dig deeper into mobile security together with Rene Graf during the mobile security workshop. There are a few slots left.

Enjoy the newsletter & hopefully see you soon in Heidelberg!
Florian

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Hi everyone,
it’s me again with another story of a toll fraud incident at one of our customers (not the same as the last time of course ;-)).
The story began basically like the last one: We received a call with an urgent request to help investigating a toll fraud issue. Like the last time I visited the site in order to get an idea on what was going on exactly. The customer has a VoIP deployment consisting of the whole UC Suite Cisco offers: Call Manager, Unity Connection for the voice mailboxes, Cisco based Voice-Gateways and of course, IP phones.

During the initial meeting I was told that the incident had taken place over the weekend, and had caused a bill of almost 100.000€ during this time period. Similar to the other incident, described two weeks ago , our customer didn’t discover it by himself but again the Telco contacted him beacause of that high bill. After the meeting I got ready to work my way through a whole bunch of log- and configuration files to analyze the situation. Spending 1 ½ days on the customer site to analyze the issue, I was able to reconstruct the incident. As stated earlier, the customer uses Cisco Unity Connection as voice mail application. Unity is reachable over a specific telephone number so that employees are able to listen to voice mail messages if they are on the road . When dialing this specific number, one has to enter the internal extension followed by a PIN for authentication. It turned out, that someone had brute forced one of the mailboxes PIN.

So how could this toll fraud issue happen by just bruteforcing the PIN of a mailbox? After successful authentication though the PIN, one is also able to configure a transfer of a call to a telephone number of your choice. Now it should become clear, where this is going…
After the bad guys retrieved the valid PIN, they configured a call transfer to some $EXPENSIVE_LONG_DISTANCE_CALL. In addition they changed the PIN in order to access the system whenever needed. As the issue started on a Friday evening (when almost everybody had already left for the weekend) nobody noticed the compromise of the mailbox. The bad guys logged in about 200 times during the weekend and configured different numbers to which the calls should be transferred. They started with some numbers located in African countries, which wasn’t successful because the configuration of the Call Manager blocked outgoing calls to such suspicious countries.

So, how could they initiate the calls nevertheless? These guys were smart. After realizing that the first approach wasn’t working they found a clever way to circumvent the restriction. They just used a so called “Call-by-Call” Provider. To use such a provider you have to prepend a provider specific prefix to the number. E.g. one prefix of a German provider is 010049. So they dialed 010049+$EXPENSIVE_LONG_DISTANCE_NUMBER and were able to circumvent the restriction on the Cisco Call Manager.

The first question which came to my mind was: Why can Cisco Unity initiate outbound calls? Well, according to our customer, there were some requirements that Unity should contact some home workers on their normal phone that new messages are present. In order to stop the potential exploit on short notice, we first configured the Call Manager denying Unity to initiate outbound calls. After digging into the configuration of Unity Connection and the Call Manager I found some configuration on the Unity connection box which enabled the attacker an easy game.

  1. The PIN was only 4 digits long.
  2. Unity Connection did not prevent the use of trivial PINs like „0000“ or „1234“.
  3. There was no restriction on to which number a call transfer could be configured.
  4. The ability to configure a call transfer over the Phone Interface is at least debatable.

These properties are a little unfortunate as Unity connection gives you all the tools you need to address the issues mentioned above. However, in this scenario the config had not been handled appropriately. So this case could basically be broken down to configuration weaknesses which favored the attacker to exploit the issue. Like in the last incident , the initial deployment and configuration was done by an external Service Provider.

So how can we assure that this won’t happen again?

  1. Use longer PINs. I recommended that the PIN should be at least 6 digits, which increases the number range you would have to bruteforce significantly, causing the attacker requiring up to 100 times as long for the attack! The password policy for the mailbox is configured in a so called authentication rule, where one can define all sort of things as for the mailbox password. In this authentication rule it was just one click to disable the use of trivial PINs.
  2. In Unity Connection, one can configure so called restriction tables to define to which numbers a call can be transferred. In the default installation there are some predefined restrictions, which didn’t work with the number plan of this particular customer.
  3. I recommended evaluating the need for configuration of call transfers over the phone, along with the advice to disable this functionality if not necessary.

All in all it is not rocket science to configure Unity Connection in a secure way, which unfortunately doesn’t mean you won’t find all kinds of scary misconfigurations. All the years at ERNW showed me this impressively.

As already said : It can cost you quite a lot of money if you do not take precautions to prevent that kind of incidents in the first place. So if you own the mentioned products (or plan on integrating them in your environment) check the configuration to ensure something like this won’t happen to you ;-)

And one more thing: If you are interested in more VoIP security coverage don’t miss out Troopers 2012 where Enno and Daniel will give a talk on how to compromise the Cisco VoIP Crypto Ecosystem.

Have a great day,
Chris

 

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I’m currently involved in creating an up to date approach to handling external connections (read: temporary/permanent connections with external parties like business partners) of a very large enterprise. Currently they have sth along the lines of: “there’s two types of external connections, trusted and untrusted. the untrusted ones have to be connected by means of a double staged firewall”.

Which – of course – doesn’t work at all in a VUCA world, for a number of reasons (the demarcation between trusted and untrusted is quite unclear – just think of mergers & acquisitions –; “business doesn’t like implementing 2-staged firewalls in some part of the world where they just signed the memorandum for a joint venture to build windmills in the desert”; firewalls might not be the appropriate control for quite some threats anyway – see for example slide 46 of this presentation– and so on). Not to mention that I personally think that the “double staged firewall” thing is based on an outdated threat model, in particular when implemented with two different vendors (for the simple reason that the added operational effort usually is not worth the added security benefit. see this post for some discussion of the concept of “operational feasibility”…).

Back to the initial point: the approach to be developed is meant to work on the basis of several types of remote connections which each determine associated security controls and other parameters. Which, at the first glance, does not seem overly complicated, but – as always – the devil is in the details.

What to base those categories on: the trust or security level of the other party (called “$OTHER_ORG” in the following) – or just assume they’re all untrusted? The protection needs of the data accessed by $OTHER_ORG? The (network) type of connection or number & type of users (unauthenticated vs. authenticated, many vs. few), the technical characteristics of the services involved (is an outbound Bloomberg link to be handled differently than an inbound connection to some published application, by means of a Citrix Access Gateway? if so, in what way?) etc.

As a start we put together a comprehensive list of questions as for the business partner, the characteristics of the connection and the data accessed and other stuff. These have to be answered by the (“business side”) requestor of an external connection. To give you an idea of the nature of questions here’s the first of those (~ 40 overall) questions:

  • Please provide details as for the company type and ownership of $OTHER_ORG.
  • More specifically: does $COMPANY hold shares of $OTHER_ORG?
  • Who currently manages the IT infrastructure of $OTHER_ORG?
  • Does $OTHER_ORG dispose of security relevant (e.g. ISO 27001) certifications or are they willing to provide SAS 70/ISAE 3402/SSAE 16 (“Type 2”) reports?
  • What is – from your perspective – $OTHER_ORG’s maturity level as for information security management, processes and overall posture?
  • How long will the connection be needed?
  • Which $COMPANY resources does $OTHER_ORG need to access?
  • Does a risk assessment for the mentioned ($COMPANY) resources exist?
  • What is the highest (data) classification level that $OTHER_ORG needs access to?
  • What is the highest (data) classification of data stored on systems that $OTHER_ORG accesses by some means (even if this data is not part of the planned access)?
  • Will data be accessed/processed that is covered by regulatory frameworks [e.g. Data Protection, PCI, SOX].
  • What would – from your perspective – be the impact for $COMPANY in case the data in question was disclosed to unauthorized 3rd parties?
  • What would – from your perspective – be the impact for $COMPANY in case the data in question was irreversibly destroyed?
  • What would – from your perspective – be the impact for $COMPANY in case the service(s) in question was/were rendered unavailable for a certain time?

We then defined an initial set of “types of connections” that dispose of different characteristics and might be handled with different measures (security controls being a subset of these). These connection types/categories included

  • “trusted business partners”/TBP (think of outsourcing partners, with strong mutual contractual controls in place etc.).
  • “external business partner”/EBP (this is the kind-of default, “traditional” case of an external connection).
  • “mergers & acquisitions [heritage]“/MA (including all those scenarios deriving from M & A, like “we legally own them but don’t really know the security posture of their IT landscape” or “somebody else now legally owns them, but they still need heavy access to our central systems, for the next 24-36 months”).
  • “business applications”/BusApp (think of Bloomberg access in finance or chemical databases in certain industry sectors).
  • “external associates”/ExtAss (“those three developers from that other organization we collaborate with on developing a new portal for some service, who need access to the project’s subversion system which happens to sit in our network”).

Next we tried to assign a category by analyzing the answers in a “point-based” manner (roughly going like: “in case we own them by 100% give a point for TBP”, “in case the connection is just outbound to a limited set of systems, give a point to BusApp”, “if it’s an inbound connection from less than 10 users, here’s a point for ExtAss” etc.), in an MS Excel sheet containing the questions together with drop-down response fields (plus comments where needed) and some calculation logic embedded in the sheet. This seemed a feasible approach, but reflecting on the actual points and assignment system, we realized that, in the end of the day, all these scenarios can be broken down to three relevant parameters which in turn determine the handling options. These parameters are

  • the trustworthiness of some entity (e.g. an organization, a network [segment], some users). pls note that _their trustworthiness_ is the basis for _our trust_ so both terms express sides of the same coin.
  • the (threat) exposure of systems and data contained in certain parts of some (own|external) network.
  • the protection needs of systems and data contained in certain parts of (usually the “own”/$COMPANY’s) network.

Interestingly enough every complex discussion about isolating/segmenting or – the other side of the story – connecting/consolidating (aka “virtualizing”) systems and networks can be reduced to those three fundamentals, see for example this presentation (and I might discuss, in another post, a datacenter project we’re currently involved in where this “reduction” turned out to be useful as well).

From this perspective a total of eight categories can be defined, with each of those mentioned parameters potentially being “high” or “low”. These would look like

Taking this route greatly facilitates the assignment of both individual connections to a category and sets of potential (generic) controls to the connection type categories, as each answer (to one of those questions) directly influences one of those three parameters (e.g. “we hold more than 50% of their shares” => increase trust; “$OTHER_ORG needs to access some of our systems with high privileges” => increase exposure; “data included that is subject to breach laws” => increase protection need etc.).

Which in turn allows a (potentially weighted) points based approach to identify those connections with many vs. few (trust|exposure|protection need) contributing factors.

 

More on this including details on the actual calculation approach and the final assignment of a category in the next part of this series which is to be published soon…

Have a great weekend

Enno

 

 

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One of our customers called us recently and asked for some support in investigating a toll fraud issue they encountered in one of their sites. Their telecommunications provider had contacted them informing them that they had accumulated a bill of 30.000€ over the last ten days.

Without knowing anything more specific, I drove to the affected site to get the whole picture.

They have a VoIP deployment based on Cisco Unified Communications Manager (CUCM, aka Call Manager) as Call Agent. The CUCM is connected via a H.323 trunk to a Cisco 2911 ISR G2 which is acting as a voice gateway. The ISR has a primary rate ISDN (PRI) Interface which is connected to the PBX of the telco. Furthermore they use a feature called Direct-inward Dial (DID) or Direct Dial-in (DDI) which is offered by Telco’s to enable calling parties to dial directly to an extension on a PBX or voice gateway.

Basically one then has a so called head number (in networking terms a prefix), together with some phone extensions. When someone from outside wants to call, he dials the head number + phone extension. Before the telco forwards the call to the ISR, the head number is stripped and only the phone extension number is forwarded to the voice gateway. E.g. when calling 12345-678, the local voice gateway will only see the 678 as called number.

After having a good overview of the design, I started to dig around in the log and configuration files to understand what exactly happened and why.

So here is what happened:

Apparently someone from some East European country had called the head number of our customer and prepended a “malicious number” (in some country in Africa) to which the ISR should setup a call.  The ISR only sees the malicious (African) number because, as said before, the head number was stripped by the telco. The malicious number was of course some $EXPENSIVE_LONG_DISTANCE_CALL ;). So the voice gateway received a call from the PBX and forwarded it back to setup the call with that number.

Before we proceed, a little bit of theory how a Cisco router decides how to forward a call, might be helpful:

In Cisco IOS, the call-routing table is configured based on so called dial-peers. These dial-peers specify how a call with a specific destination number should be forwarded.

As an example:

dial-peer voice 1234 pots
description ===incoming_calls===
incoming called number ^[2-7]..$
port 0/3/0

 

This configuration tells the router that calls to a number which matches the regular expression, should be forwarded to port 0/3/0.

As it turns out our customer uses the following dial-peer which is used for outbound calls.

dial-peer voice 5678 pots
description ===outgoing calls===
destination pattern 8T
port 1/1/1:15 -> The ISDN Interface

 

The T is a placeholder value which means that any amount of digits can follow the 8. The reason the pattern matches the digit 8 is that this digit must be dialed before the actual number.

Do I have to mention that the malicious number also starts with an 8? ;-)

So back to the presumed course of action:

The call with the malicious number hits the router. The router tries to match a configured dial-peer to forward the call.  I think you can guess which dial peer matched for the malicious number ;)

So the router sends the call back to the PBX to setup a call to the malicious number. Which is billed to our customer…

We then monitored the situation and applied a workaround (more on this in a minute) and observed what happened. As it turned out, unfortunately the attacker was able to circumvent our workaround. We discovered that is was possible to “dial-in” to the router directly by just calling the head number (as the PBX leaves the called number field empty). E.g. the called number field in the log files looks like this:

“Called Number=”

 

The router subsequently provided a line and it was possible to call the number again. Our workaround did only affect incoming calls with the number prepended, but not those where the router is the actual origin of the establishment of the call.

So how can we resolve this issue and stop the toll fraud?

As a long-term solution the configured dial patterns should be reviewed and modified to prevent such things in the future, but – given the overall complexity of the setup – this could not be done overnight.

I am currently working with the customer to develop more suitable dial patterns. I will write a follow up post with the final results when we are finished.

In the mean-time, we developed a temporary workaround to prevent this from happening again:

In Cisco IOS you can manipulate the calling or called-number with so called translation rules and you are also able to reject calls based on the called number. Our customer does not use any extension beginning with 8, so we can drop all calls on the gateway which starts with 8 as called number. So we developed the following translation-rule:

 voice translation Rule 11
  rule 1 reject /^8+/
  rule 2 reject /^$/
 voice translation-profile reject_calls
   translate called 11

 

Rule number 2 addresses the case when the called number field is empty. We mapped this profile to the dial-peers responsible for the incoming calls and specified that calls with the numbers in the translation rule must be rejected.

dial-peer voice 3456 pots
description ===Incoming_Calls===
call-block translation-profile incoming reject_calls
call-block disconnect-cause incoming call-reject
incoming called-number

 
Lessons learned:

Be careful when you develop and implement your dial patterns, as errors in this space can cost you quite a lot of money ;)

VoIP is a complex technology and this complexity can lead to all types of vulnerabilities, as Daniel and Enno are going to show in their talk at Troopers 2012. Toll fraud is still quite common and happens all the time, as you can see in an ERNW newsletter from 2009 covering a similar story from another environment.

On a side note:

The telco told us that our customer is the 8th customer affected by a toll fraud issue in the last two months. According to the telco all eight companies are in the same city, and the initial VoIP deployment at our customer was performed by an external service provider.

Maybe the same service provider has done the deployment in the other companies too…

Have a great day,
Chris

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This is a guest post by the SAP security experts of BIZEC. Enjoy reading:

On March 20th, the first BIZEC workshop will be held at the amazing Troopers conference in Heidelberg, Germany. For those still unfamiliar with BIZEC: the business application security initiative is a non-profit organization focused on security threats affecting ERP systems and business-critical infrastructures.

The main goals of BIZEC are:

  • Raise awareness, demonstrating that ERP security must be analyzed holistically.
  • Analyze current and future threats affecting these systems.
  • Serve as a unique central point of knowledge and reference in this subject.
  • Provide experienced feedback to global organizations, helping them to increase the security of their business-critical information.
  • Organize events with the community to share and exchange information.

The “BIZEC workshop at Troopers 2012” will dive into the security of SAP platforms. Still to this day, a big part of the Auditing and Information Security industries believe that Segregation of Duties (SoD) controls are enough to protect these business-critical systems.
By attending this session, InfoSec professionals and SAP security managers will be able to stop “flying blind” with regards to the security of their SAP systems. They will learn why SoD controls are not enough, which current threats exist that could be exploited by evil hackers, and how to protect their business-critical information from cyber-attacks.

Attendees can expect a high-dose of technical content covering the latest advances in the SAP security field.

The agenda is really exciting, covering hot topics such as:

  • Real-world cyber-threats to SAP systems, by Mariano Nunez Di Croce (Onapsis)
  • Five years of ABAP Code Reviews – A retrospective, by Frederik Weidemann (VirtualForge)
  • SAP Solution Manager from the hackers point of view, by Ralf Kemp (akquinet)

The workshop will be full of live demonstrations of attacks and discussions on possible mitigation techniques. Furthermore, attendees will have the pleasure of enjoying a great introduction by Gary McGraw, CTO of Cigital and pioneer in software security.

If you want to stay ahead of the threats affecting your SAP platforms, you can’t miss this workshop!

The BIZEC team

Comment by the Insinuator: We’ve prolongued the early-bird period until February 10th. We hope that helps to get your favorite event budgeted ;)


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