SF Transit System Held Hostage by Ransomware

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sf-muni-ransomware-attackWhile most ransomware incidents go unreported, the attack on San Francisco’s Municipal Transport Agency (locally known as Muni) last Black Friday was hard to keep under wraps. The conspicuous message on the screens at ticketing agents’ booths said it all: “You Hacked, ALL Data Encrypted, Contact For Key (cryptom27@yandex.com)ID:681,Enter Key.”

SFMTA, which operates fleets of buses, cable cars, historic streetcars, light railway vehicles (subway), trolley buses and a handful of other public transportations, is now part of a rapidly growing list of businesses that have been victimized by ransomware. For more about this highly disruptive menace of a malware, read our post “The Secrets Behind Ransomware’s Surging Notoriety”.

The disruption from the ransomware attack on Muni, which affected over 2,000 computers, began Friday night and continued the entire Saturday. Affected systems had their hard drives encrypted, forcing the SFMTA to switch off ticket machines at the subway stations. As a result, the commuters were able to get free rides that weekend.

People who communicated with the email address left by the hackers were told that the ransom amount was 100 bitcoins, roughly equivalent to $73,000. This is much bigger than another high-profile ransomware attack that happened earlier this year.

In that attack, the Hollywood Presbyterian Medical Center ended up paying the ransom of $17,000 worth of bitcoins. Although most attacks only cost about $600-$700, there have been reports of ransom demands reaching up to as high as $150,000.

According to the extortionist who replied at the Yandex email address, SFMTA was not a victim of a targeted attack. Rather, it was more likely that someone working at SFMTA unwittingly downloaded a trojan that actually contained the ransomware. The reason the malware was able to spread through the network was likely because the user might have been using a workstation with admin level privileges.

This is consistent with the common characteristics of ransomware. They’re usually designed to spread through non-targeted phishing attacks and exploit kits. Whomever accidentally downloads the malware becomes a victim. Not all ransomware has worm-like capabilities that allow it to propagate through the network, but sadly for SFMTA, this one did.

There has been no indication that SFMTA paid any ransom to get their systems back. In fact, it’s believed their IT folks managed to recover from backups. Backups are an effective way of recovering from a ransomware attack. However, you shouldn’t be over-dependent on them, as ransomware developers have started introducing features that enable their malware to spread to backup systems as well.

So, which particular ransomware was responsible for this attack? Apparently, that distinction goes to HDDCryptor. Upon infection, which is initiated through a downloaded executable, HDDCryptor drops several components in the Windows root folder and then runs a service known as DefragmentService. The service is responsible for maintaining the malware’s persistence in the infected system.

HDDCryptor is designed to identify currently mounted drives as well as previously connected drives and then encrypt all files. To encrypt, the malware relies on an open source disk encryption software known as DiskCryptor. DiskCryptor also enables HDDCryptor to overwrite the Master Boot Record and display the ransom message.

Because of the malware’s capability to scan the system for mounted drives and previously accessed network folders, it’s highly possible that backups (depending on how they were configured) were also infected.

This particular case brings to the fore the cyber threats faced by public transportation and utilities. While this attack fortunately did not result in any physical harm, future attacks might not be as harmless.

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