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SMS bug: Nokia's Conversation goes mute

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Comment Did you have a quiet Christmas? What about New Year? While New Years Eve is the busiest time for text messages, maybe you didn’t get any. And if you're a Nokia user, there may be a reason for that.

You might have been struck by the Curse of Silence bug that has been floating around for a while, and has been recently made public at the Chaos Computer Club. When a suitably vulnerable Nokia phone receives an SMS which has been crafted in the right way it is struck deaf and becomes unable to receive SMS text messages without a factory reset: type #7370# to do this, but you’ll lose everything.

And because MMS is triggered by SMS that’s killed too.

How does the bug work? Text messaging has lots of buried features.There are various types of text message such as those which update your internet settings or make a voicemail icon appear. Other types include paging systems, fax and email. You can also, if you know what you are doing, fake sending an email that by putting characters with those values in the right place in a message. For email the special type is "SMS and Internet Electronic Mail interworking". One of the things which differentiates an email from a text message is you have a “from” address as well as a body. To allow for this the standard uses a space between the “from” and the message.

To make all this a bit friendlier, Nokia phones using Series 60 version 2.6 or newer scan the bit before the space to look for what might be an email address – something with an @ in it. Clearly this seemed to be a good idea to the right developers at the time, but it’s a minor feature and didn’t justify significant testing. Unfortunately if the email address is longer than 32 characters, Series 60 versions 2.6, 2.8, 3.0 and 3.1 phones go into the kind of strop most families experience at Christmas and fail to communicate. Phones with version 2.6 or 3.0 don’t shrug their shoulders or slam doors. In fact they don’t give any indication that anything is wrong at all. A factory reset fixes this but will take all your personal data including the games high scores you spent so long on over Christmas. If you back your phone up after you’ve been attacked when you restore the data you restore the problem.

It’s a bit harder to deafen a version 2.8 or 3.1 phone. These need to receive 11 maliciously crafted SMS text messages and then they say that there is not enough memory to receive further messages, and something should be deleted. These phones will seem to work if you soft reset them, but the next text message of over 160 characters will kill everything again.

The work on tracking this down has been done by Tobias Engel, and was presented to the Chaos Computer Club.

(Remember that Nokia still hasn't fixed vulnerabilities that leave its more popular Series 40 phones wide open).

Of course some people are very happy about this. The doom-mongers who’ve been peddling anti-virus phone software for years finally have something that phones need protecting from. They’ve rushed to put out press releases: Fortinet and F-secure both have offerings. There is nothing the user can do to detect or prevent the problem without them. And these will only prevent, not cure the problem.

But the real Curse of Silence isn’t in the software - it’s Nokia. They’ve known about the problem for a while but do not appear to have reacted. There is nothing on the Nokia website. No press releases, no links on conversations.nokia.com ("Stores from around the neighborhood") - and nothing on the developers forum.

I know it’s Christmas [just] - but the time for Silent Night is over. ®

Catherine Keynes is a electronic engineer turned consultant who works for IT and telecoms companies. She blogs at Cat Calling.

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