Malicious SDK Spies on iPhone Users and Steals Ad Revenue, Researchers Claim

researchers have uncovered malicious behavior in a software development kit (SDK)
used by over 1,200 apps in Apple’s App Store, with a combined monthly user base
of approximately 300 million. Researchers claim the SDK steals ad revenue and
exfiltrates user data to servers controlled by its developers.

Dubbed ”SourMint”
by Snyk researchers, the SDK is provided by Chinese mobile ad platform provider
Mintegral. It allegedly contains malicious code that can spy on user activity
by logging URL-based requests made through apps that have it baked in for ad monetization.

activity is logged to a third-party server and could potentially include
personally identifiable information (PII) and other sensitive information,”
Snyk researchers explain in a blog post. “Furthermore, the SDK fraudulently
reports user clicks on ads, stealing potential revenue from competing ad
networks and, in some cases, the developer/publisher of the application.”

Mintegral allegedly
uses two methods to steal revenue from competing ad networks. By claiming
attribution for clicks that did not occur on a Mintegral presented ad, the SDK can
steal advertiser revenue that should have gone to the other ad networks.

“This seems
to be the main goal of this malicious functionality,” the researchers argue.

The second
method is less direct. The research team argues that the developer or mediator
SDK may notice that Mintegral is performing better than other ad networks,
causing positive bias toward Mintegral. Furthermore, competing ad networks can
lose revenue even when Mintegral isn’t used to serve ads, as the malicious code
intercepts the clicks even if the service isn’t enabled to serve ads.

“In this
case, ad revenue that should have come back to the developer or publisher via a
competing ad network will never be paid to the developer,” according to the

The Mintegral
SDK’s malice apparently goes even deeper. It allegedly also contains several
anti-debug protections to hide its true purpose.

“In the
code, there is a particular routine that attempts to determine if the phone was
rooted and if any type of debugger or proxy tools are in use. If it finds
evidence that it is being watched, the SDK modifies its behavior in an apparent
attempt to mask its malicious behaviors. This may also help the SDK pass
through Apple’s app review process without being detected,” the team notes.

The full research is available here. Researchers also provide what they believe is compelling evidence that the SDK exfiltrates more data than it should, potentially including personally identifiable information. The research also includes technical exploit details and remediation.

Of note,
Mintegral offers the SDK to Android developers as well. However, according to
the Snyk team, the malicious code is only present in the iOS version of the

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