Mobile Security Lab

The Wappush vulnerability, present on some Sony Ericsson handsets, has been discussed on several “places” on the web , after the release of our advisory.
We feel that, in order to avoid possible misconceptions, a few points need being remarked:

Calls in video: Performing a phone call is not required in order to allow the attack to take place. Rebooting will happen regardless of the activities being performed on the phone at the moment of the attack.

SMS messages: It is not needed to open a received SMS, for triggering the vulnerability. As shown in the video, the handset crashes upon SMS message reception, and no SMS message is displayed or present in the Message Inbox after the handset reboots.

IP packets: It is not needed to send an IP packet to a broadcast address in order to trigger the vulnerability. A crafted unicast packet, directed to the handset IP address, is all that is needed.

Operator IP Networks: We don’t know of any Mobile Operator allowing broadcast IP packets in their networks. On the other hand, at the time writing, there are Mobile Operators that assign unfiltered public IP addresses to handsets connecting to the Internet.

Tools: Despite of what has been stated elsewhere, we are not aware of any public tool that is able to exploit the vulnerability, either by using IP or SMS.

Active exploitations: Up to now, we have not heard of any hostile activity that has taken place exploiting the issue.

With regard to these specific points, we would be interested to hear of anything different.

WAP Push service can be used for delivering unsolicited data to the handset, and is typically used by Operators for providing advanced services (eg: e-mail, MMS).

The MSL-2008-001 advisory reports a Denial of Service vulnerability discovered in several SonyEricsson handsets, that allows an attacker to remotely reboot a vulnerable handset by sending a malformed WAP Push message.
Both SMS messages and UDP datagrams can be used as a transport mechanism for delivering WAP Push messages.
The vulnerability can be remotely triggered both via SMS and UDP; in the latter case the malformed message need to be sent to port 2948, that has been found open on all the handsets listed in the advisory.

The risks associated to an “UDP-based” attack scenario are not negligible in case the Operator allows reachability of the handset IP address, without doing proper filtering.
An attacker may be able to remotely reboot the handset by simply sending a carefully crafted IP datagram to the handset IP address.

Additionally:
– the handsets accept IP packets directed to a broadcast address. If broadcast packets are allowed in the network, a single UDP datagram may be sufficient for rebooting all the handsets in the target subnet.
– UDP protocol is connectionless and a single datagram is sufficient for triggering the vulnerability. Under these conditions source IP spoofing is possible, increasing the difficulties of implementing proper firewall policies and attackers tracking.

In the “SMS-based” attack scenario, an SMS, carrying the malformed WAP Push message, is able to trigger the vulnerability.
The SMS buffering performed by the Operator network brings, as a side effect, the possibility for an attacker to perform an extended Denial of Service attack against a single target.
In facts, if multiple SMS are sent to the victim, the first one will reboot the handset making it unavailable for receiving further messages.
The other messages will queue on the network side and delivery will be attempted as soon as the handset re-attaches to the network, leading to continous rebooting.
This may allow an attacker to effectively disable the use of the handset for an extended period of time.

(more…)

“You are browsing with your shiny smartphone while being connected to a wireless LAN.
Suddenly you receive a single SMS carrying a new contact information.
You don’t even have the time to check it, that your SMS inbox starts filling with unwanted messages and you don’t seem to be able to stop it…”

This is a possible scenario that may happen if you are victim of a vCard Denial of Service, described here.

The attack can be carried on, possibly in a more effective way, when a data connection is active with a Mobile Operator that assigns a public IP address, reachable over the Internet, and does not provide any filtering of incoming packets.
In this case the attack can become a truly remote Denial of Service, that can be performed over the Internet, at no cost for an attacker.
Additionally, the protocol used (UDP) allows for easy IP source address spoofing, making more difficult the tracking of an attacker or the implementation of proper firewall policies.

The following video provides a short insight of what may happens to an handset when is targeted by such an attack.
(more…)

Symmetric algorithms are often used for encrypting embedded and mobile firmware images in order to protect code and data confidentiality, AES-CBC being a typical choice.
Firmware files are usually also fully signed, but, in our experience, we met cases where encryption of some regions was the only security measure, relying only on the confidentiality of the key itself.

The lack of integrity protections, that is sometimes regarded as a minor issue in case the encryption key is maintained secret (e.g.: in hardware), may leave open some attack paths that, in some very specific cases, allow an attacker to introduce modification in selectively targeted plaintext regions.

These ideas, even if not necessarily new or applicable in a wide range of cases, are, nonetheless, here presented with the intent of stressing the need for proper integrity protection, even if the encryption key is considered secret.
Scenarios are presented for CBC mode of a generic symmetric encryption algorithm, but they may be applicable also to other modes.

(more…)