Mobile application developers using Twilio's voice and SMS software development kit (SDK) and Rest API have exposed hundreds of millions of private mobile conversations after failing to remove their hardcoded credentials from the apps, researchers revealed today.

The so-called Eavesdropper vulnerability allows attackers to harvest call records, minutes of calls, minutes of call audio recordings, and to listen in on stored recorded calls and view SMS and MMS text messages, Appthority researchers discovered.

Of the more than 1,100 iOS and Android apps Appthority reviewed, 685 were found vulnerable. The vulnerable Android apps had between 40 million and 180 million installs. Some 75 of these apps are still available on Google Play, and 102 on the App Store.

Some 33% of the vulnerable apps are business-related, according to Appthority's research report. Eavesdropper could allow an attacker to link WAV file recordings to relevant enterprise call metadata and listen in on meeting-recording apps, private recording apps, and sales-enablement services apps.

How Developers Tripped Up on Twilio

Developers forgetting to remove their hardcoded credentials from apps is nothing new. But today's mobile ecosystem can now exacerbate this misstep when it comes to potential data leakage.

The ecosystem now includes third party services like Twilio and Amazon, which allow developers to publish multiple new apps and features sets under one account, as well allowing for the white-labeling of their apps, says Seth Hardy, Appthority's director of security research.

"This allows for large levels of data leakage," Hardy warns.

In the case of Twilio, Appthority researchers stumbled across the developer vulnerability earlier this year when doing their HospitalGown research. The Twilio discovery revealed attackers could take a developer's hardcoded credentials and access all user data held in the vulnerable app, as well as any other apps the developer maintained in their Twilio account. Even apps without hardcoded credentials were at risk if they were in a developer's Twilio account, where one of the apps had the hardcoded credentials compromised, Hardy says.

Also, the same holds true even if one app is in the App Store and another is in Google Play, as long as both apps were created from the same developer's Twilio account.

Developers who remove their hardcoded credentials from current apps but forget to do the same for an older app will continue to put all their users' data at risk. That's because attackers can leverage the older vulnerable app to get access to the current ones in the Twilio account, unless the developer has reset the Twilio account token, or password. The oldest mobile-related vulnerable Twilio account dates back to 2011. 

"This not Twilio's fault. This is a developer mistake," Hardy notes. "Eavesdropper is a widespread problem on a number of platforms. Developers are re-using their code across hundreds of their apps and it is spreading that way."

The nearly 700 vulnerable Eavesdropper apps are currently available in the App Store and Google Play in 61 countries.

Patching Problems

Appthority contacted all the affected developers it lists in its report, but none have responded, Hardy says. A fix would require a developer to remove his or her hardcoded credentials from all of their apps in Twilio and reset the account token or password; the repercussions of that are likely preventing developers from issuing the fix, Hardy speculates.

"It would lock out all their users who did not update the app," Hardy explains. "Preloaded apps are hard to update and the business people who work with the developer may be hesitant to take that action."

Hardy says he's not optimistic that developers will issue updates for Eavesdropper. But Appthority has reached out to Twilio and Amazon to help nudge developers. 

Users and enterprises are typically unaware their data is exposed via the Eavesdropper vulnerability, Hardy says, adding, "There is no easy way to know, unless you can confirm the app that you are using is vulnerable."

Among the vulnerable apps and app platforms include Wrappup Apps, which is used by sales teams to record audio and annotate discussions; RingDNA, an enterprise sales platform; and Telenav, which creates branded navigation apps like Scout GPS and AT&T Navigator, the report said.

Entities that would most likely be interested in the leaked data include governments for intelligence gathering, companies looking to gain an edge through corporate espionage, and malicious attackers looking to sell the pilfered data, Hardy surmises.

"It's surprising that these vulnerabilities still exist, but a lot of people don't take data security seriously," Hardy says. "We'll probably see a lot more of the vulnerabilities in the future and it's likely to be an on-going issue."

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