By Gilbert Sison and Janus Agcaoili
Cerber ransomware has acquired the reputation of being one of the most rapidly evolving ransomware families to date. Just in May, we pointed out how it had gone through six separate versions with various differences in its routines. Several months later and it seems to have evolved again, this time adding cryptocurrency theft to its routines. This is on top of its normal ransomware routines, giving the attackers two ways to profit off of one infection.
Some details of Cerber haven’t changed, though. It still arrives via emails with an attached file:
Figure 1. Cerber arrival
The JavaScript attachment is dedicated as JS_NEMUCOD.SMGF2B, which leads to the download of the Cerber variant (detected as RANSOM_HPCERBER.SMALY5A). In most respects, this Cerber variant is identical to the versions we spotted in May, but with a new nuance to its behavior: it now targets Bitcoin wallets for theft as well.
How it goes about this is relatively simple: it targets the wallet files of three Bitcoin wallet applications (the first-party Bitcoin Core wallet, and the third-party wallets Electrum and Multibit). It does this by stealing the following files, which are associated with their respective applications:
- wallet.dat (Bitcoin)
- *.wallet (Multibit)
- electrum.dat (Electrum)
Two things are worth noting. Theft of these files does not assure that the stored Bitcoins can be stolen. The thief would still need to get the password that protects the wallet in question. In addition, Electrum no longer uses the electrum.dat file—not since late 2013.
This isn’t the only information stolen by this new Cerber variant. It also tries to steal the saved passwords from Internet Explorer, Google Chrome, and Mozilla Firefox. Note that this information theft takes place before any encryption is carried out. Saved passwords and any Bitcoin wallet information found are sent to the attackers via the command-and-control servers. It also deletes the wallet files once they have been sent to the servers, adding to the injury of the victims.
This new feature shows that attackers are trying out new ways to monetize ransomware. Stealing the Bitcoins of targeted users would represent a valuable source of potential income.
Solutions and Best Practices
Cerber’s entry vector onto systems didn’t change, so known best practices against it would still work. Educating users against opening attachments in emails from external or unverified sources would lower the risks; system administrators should also consider email policies that strip out such attachments.
Trend Micro™ Smart Protection Suites and Worry-Free™ Business Security can protect users and businesses from these threats by detecting malicious files and spammed messages as well as blocking all related malicious URLs. Trend Micro™ Deep Discovery™ has an email inspection layer that can protect enterprises by detecting malicious attachment and URLs.
Trend Micro OfficeScan™ with XGen™ endpoint security infuses high-fidelity machine learning with other detection technologies and global threat intelligence for comprehensive protection against ransomware and advanced malware. Our machine learning capabilities are tuned to account for attacks using techniques employed by ransomware like Cerber.
Indicators of Compromise
Files with the following SHA-256 hash are related to this incident:
- 6c9f7b72c39ae7d11f12dd5dc3fb70eb6c2263eaefea1ff06aa88945875daf27 – detected as RANSOM_HPCERBER.SMALY5A
