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'Curse of Silence' Hack Kills SMS Text Message Delivery

Denial-of-service attack uses malicious text message to take down mobile phone in-boxes
Text-message junkies beware: A new exploit demonstrated this week shows how an attacker can silently crash the SMS text message in-boxes of several models of Nokia mobile phones.

The so-called "Curse of Silence" attack revealed by researcher Tobias Engel at the Chaos Communication Congress in Berlin uses a specially formatted SMS message to wage a denial-of-service attack on the victim's phone. It targets a vulnerability in versions 8 through 9.2 of the Symbian operating system and so far has been shown to affect the Nokia Series 60 phone versions 2.6, 2.8, 3.0, 3.1, and the Sony Ericsson UiQ.

Engel, who did not release any exploit code for the attack, showed how SMS/MMS messaging features on the phones were affected but that otherwise, the phone remains operational. In the attack, an SMS message is sent to the victim's phone by setting the protocol identifier to "Internet Electronic Mail" with a specific format that Engel demonstrates in his paper.

Some phones immediately stop receiving text messages, while others lock up after receiving one or more of the messages.

In a video demonstration of the hack, F-Secure said even powering off and on the victimized phone won't stop the attack. "The attack messages are silent and invisible so that you will not be able to delete them," F-Secure says in its demo.

For now, there's no manual workaround for the attack. And until a firmware fix is available, network operators are advised to filter messages with TP-PID "Internet Electronic Mail" as well as email addresses of more than 32 characters, according to Engel.

"At least it is not possible to steal user data from the phones or make calls at other people's expense," Engel says. "But it shows again that mobile phones are just computers which are connected to the network all the time."

He continues: "Phone manufacturers and network operators have to make sure that there is a way to quickly deploy bug-fix firmware releases to phones, free of charge to the user."

F-Secure, meanwhile, noted in its blog that the attack may be more of annoyance. "Hopefully this exploit will not be widely used. We don't see much of a profit motive after all. Still, there were thousands of participants at this year's CCC and many of them saw the demonstration. As easy as it is to utilize the Curse of Silence, someone will surely try this for harassment," F-Secure said in its blog post.

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