SynoLocker victims who paid but still couldn’t unlock files get a second crack

If you paid $350 fee to unlock your files on a SynoLocker trapped storage device but still couldn’t access them, there may be hope thanks to a new tool from Finnish security vendor F-Secure.

The usual advice from security experts when it comes to ransomware is simply do not pay because it supports their business model. But victim’s of malware that encrypts files have little choice but to pay if they want their their files back now. That is, unless they have an unaffected backup.

Victims could pray that someone eventually develops a tool that helps them to free files commandeered by the attacker. And sometimes, security vendors do release these tools, such as Fox-IT and FireEye did recently for the CryptoLocker ransomware — but such tools are not guaranteed to arrive and even if they do, victims may need to wait months to access files that could be critical to a person’s life or a business’ ongoing operation.

So, a certain percentage of victims will pay. Some victims who pay will be able to retrieve their files. Others aren’t so fortunate. For reasons never known to the victim, their files remain locked even after paying and receiving the private ‘key’ that is meant to liberate the files.

Finnish security F-Secure has an answer for people affected by the recent SynoLocker ransomware who didn’t follow expert security advice.

SynoLocker victims are exclusively users of network attached storage devices from the vendor Synology who were not running the latest version its OS when the ransomware gang struck in early August.

SynoLocker encrypts files using Advanced Encryption Standard (AES), but uses the RSA key pair to set up the lock for which a secret RSA private key is needed to free the files. The exact method SynLocker's creators used to install the malware is still not known.

The people behind the SynoLocker campaign have, according to F-Secure, packed up shop and were selling the private keys for 5,500 systems for around $100,000 that they claimed remained sealed by the ransomware. Presumably these are systems whose owners didn’t pay.

For people who did pay but, as Artturi Lehtiö puts it, were “double crossed”, all hope is not lost. F-Secure’s new tool will work, so long as the victim has actually received the correct decryption key.

“If a victim is able to obtain the correct decryption key, the files can still be restored. For this purpose, we are today releasing a small tool, a Python script, written by us. This tool can be used to safely decrypt SynoLocker-encrypted files as long as the correct decryption key can be provided. The tool does not in any way break the encryption of files created by SynoLocker and it does not attempt to bruteforce the decryption key. It will only work, if the decryption key is already known,” explained Lehtiö.

The other situation the tool could be useful is where the victim paid for the decryption key but removed the malware.

“Instead of reinfecting your device with the malware (which is a bad idea), you can use the key together with our script to decrypt your files,” noted Lehtiö.

The example provides one more argument against victims paying ransomware attackers to unlock their files. Victims could be snared as part of a beta program littered with bugs that makes the transaction faulty.

Security vendor Kaspersky recently discovered one such example in ZeroLocker that appeared to have been a work-in-progress and did not store the information that would be required to deliver a decryption key.

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