Moxie Marlinspike has an intriguing blog post about Cellebrite, a tool used by police and others to break into smartphones. Moxie got his hands on one of the devices, which seems to be a pair of Windows software packages and a whole lot of connecting cables.
According to Moxie, the software is riddled with vulnerabilities. (The one example he gives is that it uses FFmpeg DLLs from 2012, and have not been patched with the 100+ security updates since then.)
…we found that it’s possible to execute arbitrary code on a Cellebrite machine simply by including a specially formatted but otherwise innocuous file in any app on a device that is subsequently plugged into Cellebrite and scanned. There are virtually no limits on the code that can be executed.
This means that Cellebrite has one — or many — remote code execution bugs, and that a specially designed file on the target phone can infect Cellebrite.
For example, by including a specially formatted but otherwise innocuous file in an app on a device that is then scanned by Cellebrite, it’s possible to execute code that modifies not just the Cellebrite report being created in that scan, but also all previous and future generated Cellebrite reports from all previously scanned devices and all future scanned devices in any arbitrary way (inserting or removing text, email, photos, contacts, files, or any other data), with no detectable timestamp changes or checksum failures. This could even be done at random, and would seriously call the data integrity of Cellebrite’s reports into question.
That malicious file could, for example, insert fabricated evidence or subtly alter the evidence it copies from a phone. It could even write that fabricated/altered evidence back to the phone so that from then on, even an uncorrupted version of Cellebrite will find the altered evidence on that phone.
Finally, Moxie suggests that future versions of Signal will include such a file, sometimes:
Files will only be returned for accounts that have been active installs for some time already, and only probabilistically in low percentages based on phone number sharding.
The idea, of course, is that a defendant facing Cellebrite evidence in court can claim that the evidence is tainted.
I have no idea how effective this would be in court. Or whether this runs foul of the Computer Fraud and Abuse Act in the US. (Is it okay to booby-trap your phone?) A colleague from the UK says that this would not be legal to do under the Computer Misuse Act, although it’s hard to blame the phone owner if he doesn’t even know it’s happening.