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Update RansomEXX Trojan attacks Linux systems
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[Image: ransomexx-trojan-linux-01-1024x899.png]


Quote:We recently discovered a new file-encrypting Trojan built as an ELF executable and intended to encrypt data on machines controlled by Linux-based operating systems.

After the initial analysis we noticed similarities in the code of the Trojan, the text of the ransom notes and the general approach to extortion, which suggested that we had in fact encountered a Linux build of the previously known ransomware family RansomEXX. This malware is notorious for attacking large organizations and was most active earlier this year.

RansomEXX is a highly targeted Trojan. Each sample of the malware contains a hardcoded name of the victim organization. Moreover, both the encrypted file extension and the email address for contacting the extortionists make use of the victim’s name.

Several companies have fallen victim to this malware in recent months, including the Texas Department of Transportation (TxDOT) and Konica Minolta.

Technical description:

The sample we came across – aa1ddf0c8312349be614ff43e80a262f – is a 64-bit ELF executable. The Trojan implements its cryptographic scheme using functions from the open-source library mbedtls.

When launched, the Trojan generates a 256-bit key and uses it to encrypt all the files belonging to the victim that it can reach using the AES block cipher in ECB mode. The AES key is encrypted by a public RSA-4096 key embedded in the Trojan’s body and appended to each encrypted file.

Additionally, the malware launches a thread that regenerates and re-encrypts the AES key every 0.18 seconds. However, based on an analysis of the implementation, the keys actually only differ every second.

Apart from encrypting the files and leaving ransom notes, the sample has none of the additional functionality that other threat actors tend to use in their Trojans: no C&C communication, no termination of running processes, no anti-analysis tricks, etc.

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