Mysterious ‘MMS Fingerprint’ Hack Used by Spyware Firm NSO Group Revealed

upstart writes:

Mysterious 'MMS Fingerprint' Hack Used by Spyware Firm NSO Group Revealed:

The existence of a previously unknown infection technique used by spyware firm NSO Group is suggested by a single line in a contract between NSO and the telecom regulator of Ghana.

The contract is within the documentation of the ongoing court case between WhatsApp and NSO. Labeled under 'Infection Assisting Tools' is a single entry titled 'MMS Fingerprint'. NSO claims it can reveal the target device and the OS of the target device, 'without user interaction, engagement or message opening', and can be used against Android, Blackberry, and iOS.

There is (or has been) no known MMS fingerprint infection route. Cathal McDaid, VP of technology at Swedish telecoms security firm Enea investigated to learn more.

Since multiple device manufactures can be targeted, McDaid decided to look at the MMS flow rather than the individual devices. The MMS flow, writes McDaid, is somewhat 'messy': "Confusingly, sometimes the MMS flow is not using MMS."

MMS was introduced when not all phones were MMS compatible. So, the developers introduced a fall-back to a type of SMS known as a binary SMS (WSP Push), used to notify the recipient MMS device's user agent that an MMS message is waiting for retrieval.

Similarly, retrieval of the message is also not specifically 'MMS' - it is an HTTP GET request to the URL address contained in the waiting message. "The interesting thing here," writes McDaid, "is that within this HTTP GET, user device information is included. It was suspected that this may be the point that targeted device information could be leaked, and the MMS Fingerprint could be 'lifted'."

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