I didn’t write about the recent security breach that disclosed tens of thousands of e-mail addresses and ICC-IDs of iPad users because, well, there was nothing terribly interesting about it. It was yet another web security breach.
Right after the incident, though, I was being interviewed by a reporter that wanted to know what the ramifications of the breach were. He specifically wanted to know if anything could be done with those ICC-IDs, and if the disclosure of that information was worse than people thought. He didn’t like the answer I gave him, which is that no one knows yet: that it’s too early to know the full effects of that information disclosure, and that both the good guys and the bad guys would be figuring it out in the coming weeks. And, that it’s likely that there were further security implications of the breach.
Seems like there were:
The problem is that ICC-IDs—unique serial numbers that identify each SIM card—can often be converted into IMSIs. While the ICC-ID is nonsecret—it’s often found printed on the boxes of cellphone/SIM bundles—the IMSI is somewhat secret. In theory, knowing an ICC-ID shouldn’t be enough to determine an IMSI. The phone companies do need to know which IMSI corresponds to which ICC-ID, but this should be done by looking up the values in a big database.
In practice, however, many phone companies simply calculate the IMSI from the ICC-ID. This calculation is often very simple indeed, being little more complex than “combine this hard-coded value with the last nine digits of the ICC-ID.” So while the leakage of AT&T’s customers’ ICC-IDs should be harmless, in practice, it could reveal a secret ID.
What can be done with that secret ID? Quite a lot, it turns out. The IMSI is sent by the phone to the network when first signing on to the network; it’s used by the network to figure out which call should be routed where. With someone else’s IMSI, an attacker can determine the person’s name and phone number, and even track his or her position. It also opens the door to active attacks—creating fake cell towers that a victim’s phone will connect to, enabling every call and text message to be eavesdropped.
More to come, I’m sure.
And that’s really the point: we all want to know—right away—the effects of a security vulnerability, but often we don’t and can’t. It takes time before the full effects are known, sometimes a lot of time.
And in related news, the image redaction that went along with some of the breach reporting wasn’t very good.
Posted on June 21, 2010 at 5:27 AM •
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