‘MaMi’ Mac Malware Hijacks DNS Settings

Researcher Patrick Wardle has analyzed what seems to be a new piece of malware designed to hijack DNS settings on macOS devices. The threat has other capabilities as well, but they do not appear to be active.

The malware, dubbed OSX/MaMi by Wardle based on a core class named “SBMaMiSettings,” is currently only detected – at least based on its signature – by ESET and Ikarus products as OSX/DNSChanger.A and Trojan.OSX.DNSChanger. However, other vendors will likely create signatures for the threat in the upcoming hours and days.

The researcher obtained a sample of MaMi after a user reported on the Malwarebytes forums that a teacher’s Mac had been infected. The user reported that the DNS servers on the compromised system were set to 82.163.143.135 and 82.163.142.137, and they kept changing back after being removed.

Wardle has not been able to determine how the malware is being distributed, but he has found it on several websites. The expert believes the threat has likely been delivered via email, fake security alerts and pop-ups on websites, or social engineering attacks.

The sample analyzed by the researcher acts as a DNS hijacker, but it also contains code for taking screenshots, simulating mouse events, downloading and uploading files, and executing commands.

The malware does not appear to execute any of these functions, but Wardle says it’s possible that they require some attacker-supplied input or other preconditions that his virtual machine may not have met. The researcher says he will continue to investigate.

Once it infects the system, the malware invokes the security tool and uses it to install a new certificate obtained from a remote location.

“OSX/MaMi isn’t particular advanced – but does alter infected systems in rather nasty and persistent ways,” Wardle explained. “By installing a new root certificate and hijacking the DNS servers, the attackers can perform a variety of nefarious actions such as man-in-the-middle’ing traffic (perhaps to steal credentials, or inject ads).”

The easiest way to determine if a macOS system is infected with the MaMi malware is to check DNS settings – the threat is present if the server is set to 82.163.143.135 and 82.163.142.137. The malware does not appear to be designed to target Windows devices.

The most well known DNS-changer malware is DNSChanger, a threat that made rounds in the years leading up to 2011 and which changed DNS settings as part of clickjacking and ad replacement fraud schemes. DNSChanger affected both Windows and OS X machines, and millions of devices worldwide were at risk of losing Internet connectivity after authorities took down its infrastructure.

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