Mobile Security Lab

Here we are with another sample of our attack technique described in the “Hijacking Mobile Data Connections” post. Today we are going to show you how the attack can have a significantly deeper impact depending on the design of the target handset: specifically, some defects in the provisioning messages processing code, together with a less than optimal User Interface design, lead to a significant advantage for an attacker trying to compromise the device.
In this case no ‘social engineering’ or spoofed messages are required.

As described in our MSL-2009-001 advisory (“Samsung Missing Provisioning Authentication”), we have identified some handsets that don’t perform proper authentication of incoming SMS Provisioning messages. They never display the source of the message; moreover, and much more worrying, they accept both authenticated and unauthenticated provisioning messages without giving to the user any hint of the nature of the message itself. To install the configuration inside it, user simply has to open the incoming message, while no authentication is in effect.

The following video shows how the attack is performed against these devices.

It is important to highlight that both unauthenticated messages and authenticated ones (whether by USERPIN or NETWORKPIN mechanism) are presented to the user in exactly the same way.
This has a deep impact on the security level perceived by the user: a competent one, in fact, could base its judgement of the message authenticity on the fact that it is authenticated by a specific mechanism. In order to produce a correct NETWORKPIN-authenticated message, the sending party has to know the IMSI of the victim, which is usually considered a private information, known only to the user itself and to the operator he belongs to.
The user, seeing that he is not asked to input any PIN, is led to think that the provisioning message is of the NETWORKPIN-authenticated type, and that, being so, it has to come from the operator’s systems; this reinforce, in the user, the belief that he can safely accept the new configuration.

The attack we presented at BlackHat Europe 2009 showed how it could be possible to take complete control of mobile originated data connections, by using a standard Provisioning mechanism, exploiting the ability to deliver configuration messages to handsets and performing social engineering on user by means of spoofing techniques.

Provisioning is a process that allows for remote configuration of Mobile Devices, and is tipically used by Mobile Operators for sending handsets the correct configuration for using data connections (eg: Internet access, MMS…)

Userpin is one of the available security mechanisms for performing the Provisioning process.
When using such mechanism the Mobile Operator sends a text SMS, advising the user that he is going to receive a configuration message, and a PIN code, that will be used for installing the configuration.
The configuration message is then sent as a second SMS. The user needs to insert the received PIN code, and then the configuration will be installed.

Abusing the Provisioning process can be performed in multiple ways. The solution we presented at BlackHat relies on changing the DNS address with the Userpin mechanism, but other options are possible.

Our paper can be downloaded here and slides here

A demo of the attack is now also available in the video below, where two samples of the attack have been performed.

Further information and details are reported in the following.

We will provide additional samples and variations, while covering handsets from more manufacturers, in the next few days.

(more…)

We’re back from Black Hat Europe ’09; as always it’s been an interesting experience.

In the next few days we’ll post here the details of the work we presented there (“Hijacking Mobile Data Connections”), but since a few articles have been published, we feel that stressing a few concepts is needed.

The attack we presented does not rely on a single vulnerability but is the result of the possibility of “abusing” a standard protocol that allows for mobile devices remote reconfiguration.

The problem affects all the devices which sports an OMA Provisioning client and that are used on a network that doesn’t implement effective filtering of provisioning messages coming from untrusted sources; the brand, model and other similar details play a marginal role in all this.

In our opinion, support for OMA provisioning is not a problem ‘per se’, but it is rather the ability to abuse it that should be regarded as the problem.
So, the handsets could be considered more as possible targets of the attack, rather than the root cause of the problem itself. Some improvements on the handset side could help in mitigating the problem, but they could hardly entirely avoid this kind of attack.

The ability to process OMA provisioning messages really depends on several factors: brand, model, firmware version; providing explicit indications on which handset is a possible target could be easily prone to error.
As far as we know a large number of models, from different Manufacturers, support the provisioning client, but, in order to avoid possible misunderstanding, we prefer not to mention brand and models unless specific vulnerabilities in the client are identified.

In summary: support of the OMA provisioning client, as specified in standard, along with the possibility to receive provisioning messages from untrusted sources, should be the main criteria for evaluating a risk scenario.

Stay tuned for the rest of the story.

MSL-2008-001 vulnerability raised a significant attention; we have now decided to disclose its technical details. We decided to proceed with the disclosure in order to stimulate public analysis and contribution, hoping to increase awareness about this issue and ultimately help protection against it.

The following description is based on our tests and our inference of what happens inside the device.
Unfortunately, researching vulnerabilities on such devices is a long and painful work, because of the lack of documentation, testing tools and debuggers, so we cannot ultimately state what happens at the code level.

All evidences are towards a vulnerability occurring in the parsing of WAP Push header; the code devoted to such parsing appears to be used for processing packets received both on SMS and IP.

We strongly believe that the specific issue resides in the improper handling of incorrect size fields inside the WAP Push headers.

WAP is actually a large framework, into which WSP is in charge of content delivery. A reference document describing WSP protocol can be found here:

http://www.openmobilealliance.org/tech/affiliates/LicenseAgreement.asp?DocName=/wap/wap-230-wsp-20010705-a.pdf

WSP makes extensive use of size fields; our tests have tracked a few fields that, if incorrectly specified, will lead the vulnerable handsets to an error condition, such as rebooting or system freezing. More specifically, the vulnerability will be triggered if, in such fields, the specified length is larger than the actual amount of bytes.

Since WAP content can be carried both over SMS and IP protocol, we will make use of the latter to show an example; this enables us to use Wireshark to better explain the data structures.

The following pictures show the capture of 2 sample IP packets that, when sent to the handset, will make it reboot; they have been opened with Wireshark, even though they are marked (obviously) as ‘malformed’.
The lower pane shows the hexadecimal representation of WAP payload.

Fig 1 – MSL-2008-001-1

Figure 1 shows one of the first formats we researched: this is a WAP Push message carrying a “multipart” Content-Type payload. According to the specifications, the 2 bytes circled in the screenshot refer to the multipart payload headers:
Header Length: 0x0a
Content Length: 0x1

In the remaining part of the  packet there are only 0xa bytes, and no byte is referenced by the 0x1 of the Content Length. This is enough for triggering the vulnerability; changing the Content Length to 0x0 would fix the header and the payload would be normally processed by the handset without any consequence.

Let’s see another example:

Fig 2 – MSL-2008-001-2

This sample does not use any multipart content, it just consists of the WAP Push packet header, without any payload. The specified Header Length (3rd byte) is 0x1c bytes long, while there
are just 0x1b remaining bytes in the header. Changing the Header-Length to the correct value of 0x1b would fix the header resulting in an inoffensive WAP Push packet.

These malformed WAP Push packets are to be sent over UDP, but the very same payload can be embedded in a properly formatted SMS.

We are not sure that all the possible attack vectors have been identified; and the two samples, even if they yield the same effect, may actually be due to different code execution flows.

Besides, it seems that the vulnerability occurs quite early in the processing of the WAP packet, because the UI settings are not able to influence in any way the processing of such packets.
The vulnerability occurs long before anything is displayed on the UI, and the received SMS is not even saved in the Inbox.

The ‘closed’ OS and the characteristics of this vulnerability suggest us that a protection on the network side could be a viable alternative to that on the handset side, but other options may apply too.