Signal vs. Cellebrite: What You Need to Know

If you’re part of legal investigations that involve any kind of electronic data, you need to know what’s happening between Signal and Cellebrite.

Cellebrite makes one of the industry’s most commonly used digital forensics tools, and Signal CEO Moxie Marlinspike has recently publicized alleged vulnerabilities in Cellebrite’s security measures. Continuing to use outdated versions of Cellebrite, especially without other best practices of digital forensics in place, could open the door for system hacks as well as opposing counsel questioning the integrity of your evidence.

These types of legal proceedings can cause substantial disruptions in forensic labs worldwide.  Forensic extractions and analysis would have to pause for the duration of the imaging process; forensic labs would need to relocate sensitive data to other platforms; ultimately the legal costs associated with these additional acquisitions and analysis could be significant. Luckily, there’s a few relatively simple steps you can take now to prevent the astronomical time and expense it would take to deal with any spoliation issues.

The Background

Signal and Cellebrite exist on two opposite sides of the technology spectrum: Signal is a messaging app that offers end-to-end encrypted messaging. Digital privacy is their primary selling point. Cellebrite is a digital forensics company.  When law enforcement seizes an electronic device for an investigation, there are good odds that someone, somewhere is using Cellebrite technology to unlock it and collect data. That means one of their primary selling points is the ability to circumvent privacy measures when the situation calls for it. You can understand why two such companies would end up at odds. It’s a never-ending cat and mouse game: a win in forensics is normally seen as a loss in security and vice versa.

In a blog post, Signal CEO Moxie Marlinspike made several serious allegations against Cellebrite’s security protocols:

  • That Cellebrite has not updated some of their source code files since 2012, despite hundreds of updates to these files becoming available since then.

  • That because most of the data extracted by Cellebrite comes from third-party apps rather than the device itself, it would be possible for any untrusted app developer to put files in their apps that would corrupt Cellebrite output and reporting. 

  • That if such an exploitation were to occur, not only would it undermine that particular collection, but any prior and future collections done with that same Cellebrite device.

  • That “Industry-standard exploit mitigation defenses are missing, and many opportunities for exploitation are present.”

  • That Cellebrite appeared to also include unlicensed iTunes software, opening the door for legal challenges from Apple to Cellebrite and its users.

Marlinspike’s blog post also concluded with some “completely unrelated news” about how new updates to Signal would feature files in app storage for “aesthetic purposes.”

Some have interpreted this to mean that not only is Marlinspike saying these vulnerabilities in Cellebrite exist, but that he intends to actively use his own Signal app to wreak havoc on Cellebrite investigations.

Of course, no can know for sure, but if that’s true it poses a substantial threat. Signal had over 40 million users as of January 2021, so it’s only a matter of time until law enforcement ends up investigating a phone where the app is installed.

Other Important Context

While it’s not exactly wrong to say that some of these vulnerabilities look like rookie mistakes to an outsider, it’s important to recognize that unlike the consumer-facing Signal app, Cellebrite is not intended for use by laypeople. Anyone using Cellebrite to extract data from a device is most likely an expert in digital forensics who’s taking other precautions to prevent the kind of corruption that Marlinspike describes.

Cellebrite’s original customer base consisted of government and law enforcement agencies.  Many of these organizations use forensic workstations that are isolated from internet accessible devices. They also sanitize their workspaces between cases to avoid cross-contamination between different devices’ data. Assuming these best practices are in place, the risk of rogue executables coming from mobile devices the way Signal suggests is incredibly low.  

However, as Cellebrite has grown, so has their number of private sector clients who use workstations that rely on the same networks as other company devices. That means that if someone were to exploit the vulnerabilities that Marlinspike mentions in his blog, the ramifications could be company wide, not just a matter of corrupting one device.

More remote collections in light of the pandemic also complicates things. In light of these developments, the concern of untrusted data on a mobile device corrupting an acquisition is real; unlikely, but real none the less. We also have to remember that in forensics, theoretical possibilities matter. Ideally, you do not just want to prove that no one tampered with your data, but that it was highly unlikely that anyone could have tampered with your data.

The publicization of Cellebrite’s vulnerabilities is already having real-world consequences. In Maryland, a defense attorney named Ramon Razos is asking for a re-trial because law enforcement relied heavily upon Cellebrite evidence to convict his client.

So… can I keep using Cellebrite in my investigations?

The short answer is, yes. You can keep using Cellebrite and significantly reduce your risk of data spoliation with just a few best practices of forensics. Namely, run the most recent version of Cellebrite.

According to Vice, Cellebrite issued an update less than a week after Marlinspike published his blog post. While Cellebrite did not explicitly say that these patches were meant to address Marlinspike’s grievances, the timing certainly makes it look that way. In the same Vice article, Cellebrite allegedly asserts that “Based on our reviews, we have not found any instance of this vulnerability being exploited in the real-life usage of our solutions.”

Again, those using Cellebrite should be forensic experts with other tricks up their sleeve. They’re not relying entirely on Cellebrite technology for effective preservation, but some combination of Cellebrite technology and their own failsafe measures. 

A forensic analyst should always spot check their work by manually reviewing the raw files to confirm the forensic software parsed out the intended artifacts. Spot checks of the data on the physical device can also reassure the investigative team that they have maintained data integrity.

If you’re a lawyer who’s paying someone else to handle your forensics, make sure your vendor is aware of the current Cellebrite situation and has applied the most recent patches. It’s also totally fair to ask your vendor what other non-Cellebrite measures are in place to ensure data integrity and defensibility. Are they sanitizing work stations between collections? Are they spot checking their data? You deserve to know.

While the risk of data corruption is most likely far lower than Marlinspike wants Cellebrite customers to believe, it is there, and the consequences of an exploitation are too great not to check all your bases.

If you have any other questions about digital forensics, you can reach out to Contact at info@contactdiscoveryservices.com.

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