sb-eu logo
Story image

Cisco Talos releases PyLocky ransomware decryptor - but there's a catch

14 Jan 2019

Security firm Cisco Talos has released a free decryption tool for Windows users affected by the PyLocky ransomware – but it won’t work for everyone.

PyLocky is an imitation of the notorious ‘Locky’ ransomware, except it is written in a programming language called Python. The ransomware tries to mimic other ransomware families. While ransomware is a menace to those who happen to be infected by it, decryption tools can often reverse the damage. In PyLocky’s case Cisco Talos managed to create a decryption tool, but there’s a very big catch.

The tool will only work for those who managed to capture a PCAP of the outbound connection attempt to the ransomware’s command & control servers – a connection that happens mere seconds after the infection. In a nutshell, the PyLocky ransomware decryptor will only work on machines that have network traffic monitoring capabilities.

According to Cisco Talos, PyLocky generates a random user ID and password when it executes. It also gathers information about the infected machine by using WMI wrappers.

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

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." 

Each file is then overwritten with a ransom demand.

For those victims who do use network monitoring software, they just need to download the decryptor to their infected machine, download WinPcap, specify the PCAP file with IV and password, and wait for the decryptor to do its thing. The company says that during its testing phase, the decryptor was able to recover three infected systems, however very large files 4GB and over may not be able to be decrypted.

The company says the decryptor is built for use on Windows systems and takes no responsibility for misuse of the decryptor tool.

“Talos encourages users never to pay an attacker-demanded ransom, as this rarely results in the recovery of encrypted files. Rather, victims of this ransomware should restore from backups if their files cannot be decrypted. Just as in the June 2017 Nyetya attack, Talos has observed on numerous occasions that attackers who are demanding ransoms may have no way to communicate with victims to provide a decryptor,” says Cisco Talos.  

Story image
Gartner predicts 75% of CEOs to be liable for cyber-physical security incidents by 2024
The nature of CPSs means incidents can quickly lead to physical harm to people, destruction of property or environmental disasters – and Gartner’s new research indicates that these incidents will increase drastically in the next few years if the lack of spending on these assets continues.More
Story image
The guide to digital security in unstable times
An increase in vulnerability across different sectors has meant that 2020 has seen more than its fair share of cybersecurity incidents. One of the most effective ways to combat the perils of today’s cyber-threats is to gain a better knowledge of the threat vectors looming over the heads of organisations. More
Story image
Video: 10 Minute IT Jams - The benefits of converged cloud security
Today, Techday speaks to Forcepoint senior sales engineer and solutions architect Matthew Bant, who discusses the benefits of a converged cloud security model, and the pandemic's role in complicating the security stack in organisations around the world.More
Story image
Zero trust is the way to secure the distributed workforce - Empired
Existing security solutions need to evolve to accommodate the new remote workforce.More
Story image
Proofpoint enhances security awareness training platform
Available in Q4 2020, the platform will integrate more closely with Proofpoint’s best-in-class threat intelligence.More
Story image
Proofpoint and CyberArk extend partnership to further safeguard high-risk users
“Our CyberArk partnership extension provides security teams with increased detection and enhanced adaptive controls to help prevent today’s most severe threats."More