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Monday, 14 January 2019 08:29

Talos develops decryption tool for PyLocky ransomware

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Talos develops decryption tool for PyLocky ransomware Pixabay

Cisco's Talos Intelligence Group has released a free decryption tool for recovering files that have been encrypted by the PyLocky Windows ransomware, a family of malware written in Python and masquerading as a variant of the Locky ransomware.

A statement from Talos said there was one requirement: the tool could be used only in cases where the initial PyLocky command and control traffic of an infected machine had been captured.

Researcher Mike Bautista, who developed the tool, wrote: "If the initial C2 traffic has not been captured, our decryption tool will not be able to recover files on an infected machine.

"This is because the initial callout is used by the malware to send the C2 servers information that it uses in the encryption process."

He explained that when PyLocky ran on an infected machine, it generated a random user ID and password and collected information about the machine using WMI wrappers.

PyLockyRansom

The ransom note left by the PyLocky ransomware. Courtesy Talos

The ransomware also generated a random initialisation vector or IV which was base64 encoded and sent to the C2 server along with the system information collected by PyLocky.

"After obtaining the absolute path of every file on the system, the malware then calls the encryption algorithm, passing it the IV and password," Bautista said.

"Each file is first base64-encoded before it is encrypted. The malware appends the extension '.lockedfile' to each file it encrypts - for example, the file 'picture.jpg' would become 'picture.jpg.lockedfile'. The original file is then overwritten with the attacker's ransom note."

He discouraged users from paying any ransom demanded by the creators of such malware as it rarely resulted in the recovery of files.

The free decryption tool can be downloaded here.

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Sam Varghese

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Sam Varghese has been writing for iTWire since 2006, a year after the site came into existence. For nearly a decade thereafter, he wrote mostly about free and open source software, based on his own use of this genre of software. Since May 2016, he has been writing across many areas of technology. He has been a journalist for nearly 40 years in India (Indian Express and Deccan Herald), the UAE (Khaleej Times) and Australia (Daily Commercial News (now defunct) and The Age). His personal blog is titled Irregular Expression.

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