Disaster as CryptoWall encrypts US firm's entire server installation

Paying ransom was quicker than backups

"Here is a tale of ransomware that will make your blood run cold," announced Stu Sjouwerman of security training firm KnowBe4 in a company newsletter this week and he wasn't exaggerating.

One of his firm's customers contacted him on 14 October for advice on how to buy Bitcoins after all seven of its servers containing 75GB of data had been encrypted by a recent variant of the hated CryptoWall ransom Trojan.

An admin had clicked on a phishing link which was bad enough. Unfortunately, the infected workstation had mapped drives and permissions to all seven servers and so CryptoWall had quickly jumped on to them to hand the anonymous professional a work day to forget.

The organisation, a US-based non-profit with a headcount running into the hundreds, had backups but discovered to their shock that reinstating them would consume days, leaving the entire enterprise twiddling its thumbs. Admins were also unsettled by the possibility that some of those backups had not been verified and might not even work.

Staring at expensive downtime, who did they call? Ironically, the ransom criminals themselves on the assumption that they would supply the decryption key within hours and this would be the quickest way get all the data back.

The problem was that the firm's IT team knew little about getting hold of Bitcoins, a process that requires signing up to an currency exchange after time-consuming security checks have been carried out. This can take days on its own.

In a stroke of luck, the victim firm had recently taken Kevin Mitnick's Security Awareness Training course developed by the famous hacker in conjunction with Sjouwerman's KnowBe4 and this came with the guarantee to pay ransoms should the customer subsequently fall prey to an attack (participants have to undertake regular phishing simulations to qualify).

KnowBe4 had the Bitcoins in its wallet and duly paid the $500 ransom (1.33 Bitcoins), quickly receiving the encryption key the affected firm used to retrieve its data. Even after paying for the decryption key, the whole process still took an exhausting 18 hours.

One database had been corrupted during encryption and that had to be restored from a backup.

When Techworld spoke to Sjouwerman, he admitted that paying malware ransoms is controversial but he described it as a simple business decision for the victim.

"The problem people run into is 'how am I going to get Bitcoins," he said. As bad as paying the ransom was, it was still a much lower price than bringing the organisation to a standstill for up to a week.

He believes that CryptoWall 2.0 will reliably deliver encryption keys to paying victims but Techworld would like to point out that this can't be guaranteed. Anecdotally, that has not always been the case for all ransomware and variants.

His advice for defending against this type of threat:

1. Never to take shortcuts such as mapping drives to critical servers from any admin workstation. Use a tool to make remote connections when they are needed.

2. Don't just make backups but test the restore function too.

3. Consider investing in whitelisting to lock down the software that can run.

4. Enrol staff in a security-awareness programme that includes training to defend against phishing attacks. This is obviously KnowBe4's marketing message in publicising the incident but it is probably reasonable advice. Many employees have never heard of ransomware.

5. Assume something like CryptoWall will happen eventually and develop a security culture to cope.

"CryptoWall is in full swing," said Sjouwerman, matter-of-factly.

With good timing, Dell SecureWorks this week reported that CryptoWall infections have carried on rising through September and October despite greater awareness, reaching 830,000 worldwide, including 40,000 in the UK.

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