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Mobile Security

04:00 PM
Larry Loeb
Larry Loeb
Larry Loeb

Chinese-Linked APT41 Can Read Your Texts

New malware family is designed to have the ability to monitor as well as save SMS traffic from specific phone numbers, IMSI numbers and keywords for subsequent theft.

FireEye Mandiant says that it has recently discovereda new malware family being used by APT41 (a Chinese APT group) that is designed to have the ability to monitor as well as save SMS traffic from specific phone numbers, IMSI numbers and keywords for subsequent theft. They say the malware, MESSAGETAP, was deployed as part of Chinese espionage efforts.

APT41 has previously been described by FireEye in a report as a dual cybercrime (finanacially motivated) and espionage operation.

The current operation was found during an August 2019 FireEye investigation at a telecommunications network provider within a cluster of Linux servers. This is an efficient location to place a data stealer because of the high amount of SMS traffic that goes through this part of the system.

Initially loaded by an installation script, MESSAGETAP is a 64-bit ELF data miner. Once installed, the malware checks for the existence of two files: keyword_parm.txt and parm.txt. It attempts to read the configuration files every 30 seconds. If either exist, the contents are read and XOR decoded.

The researchers say that, "The first file (parm.txt) is a file containing two lists:

      1) imsiMap: This list contains International Mobile Subscriber Identity (IMSI) numbers. IMSI numbers identify subscribers on a cellular network.


               2) phoneMap: The phoneMap list contains phone numbers.

The second file (keyword_parm.txt) is a list of keywords that is read into keywordVec."

Once loaded into memory, both files are deleted. Then, the serious eavesdropping begins.

It uses the libpcap library to listen to all traffic and parses network protocols, starting with Ethernet and IP layers. It continues parsing protocol layers including SCTP, SCCP and TCAP. Finally, the malware parses and extracts SMS message data from the network traffic.

FireEye says that the malware will search the SMS message contents for keywords found in the keywordVec list, compares the IMSI number with numbers from the imsiMap list, and checks the extracted phone numbers with the numbers in the phoneMap list. The presence of both the phone number and the IMSI number used together signifies a highly targeted attack. The keyword list was composed of terms that the Chinese would find interesting, such as the names of political \r\nleaders, military and intelligence organizations as well as political movements at odds with the Chinese government.

But more is going on here. FireEye found that the threat actor was interacting with call detail record (CDR) databases to query, save and steal records during this same intrusion. The CDR records corresponded to foreign high-ranking individuals of interest to the Chinese intelligence services.

It doesn't seem surprising that a nation-state threat actor would have this sort of interception capability. It is unusual to find such a detailed look at an operational tool as FireEye has provided. They see an evolving Chinese targeting trend focused on both upstream data and targeted surveillance. It is only prudent that due to tools like MESSAGETAP both users and organizations consider the risk of unencrypted data being intercepted several layers upstream in their cellular communication chain.

— Larry Loeb has written for many of the last century's major "dead tree" computer magazines, having been, among other things, a consulting editor for BYTE magazine and senior editor for the launch of WebWeek.

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