Malicious Behavior Found in Advertising SDK Used by 1,200 iOS Apps

Researchers at developer security company Snyk claim to have identified malicious behavior in an advertising SDK that is present in more than 1,200 iOS applications offered in the Apple App Store.

The SDK has been developed by Mintegral, a China-based mobile advertising platform provider that has offices in the United States, Europe and Asia. Snyk says it has only identified the malicious behavior in iOS versions of the Mintegral advertising SDK; the code does not appear to be present in Android versions. The company estimates that the 1,200 impacted iOS apps are downloaded roughly 300 million times every month.

According to Snyk, its researchers discovered what they described as malicious code in versions of the iOS SDK going back to 5.5.1 (released in July 2019). The code on which they conducted their analysis was obtained from Mintegral’s official GitHub account.

Snyk says the SDK, which it has dubbed “SourMint,” can allow Mintegral to steal revenue from other ad networks used by applications integrating the SDK. In addition to ad fraud, it allegedly harvests URLs accessed through applications that use the SDK — as well as other system and device information — which could provide the vendor access to highly sensitive information, as demonstrated by Snyk in a video.

SecurityWeek has reached out to Mintegral for comment and will update this article if the company responds.

“Developers can sign up as publishers and download the SDK from the Mintegral site. Once loaded, the SDK injects code into standard iOS functions within the application that execute when the application opens a URL, including app store links, from within the app,” Snyk researchers explained. “This gives the SDK access to a significant amount of data and even potentially private user information. The SDK also specifically examines these open URL events to determine if a competitor’s ad network SDK was the source of the activity.”

The company has pointed out that this behavior appears to be intentional as the SDK looks for signs of a debugger and proxy tools before initiating these activities. This could be an attempt to determine if it’s being analyzed and possibly a method for bypassing Apple’s review process for applications published on the App Store, as it behaves differently if its actions are being watched.

“As the first malicious SDK of this kind to infiltrate the iOS ecosystem, SourMint was very sophisticated. It avoided detection for so long by utilizing various obfuscations and anti-debugging tricks,” said Danny Grander, co-founder and CSO of Snyk. “Developers were unaware of the malicious package upon deploying the application, allowing it to proliferate for more than a year.”

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