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Alert (TA13-309A)

CryptoLocker Ransomware Infections

Original release date: November 05, 2013 | Last revised: November 18, 2013

Systems Affected

Microsoft Windows systems running Windows 8, Windows 7, Vista, and XP operating systems

Overview

US-CERT is aware of a malware campaign that surfaced in 2013 and is associated with an increasing number of ransomware infections. CryptoLocker is a new variant of ransomware that restricts access to infected computers and demands the victim provide a payment to the attackers in order to decrypt and recover their files. As of this time, the primary means of infection appears to be phishing emails containing malicious attachments.

Description

CryptoLocker appears to have been spreading through fake emails designed to mimic the look of legitimate businesses and through phony FedEx and UPS tracking notices.  In addition, there have been reports that some victims saw the malware appear following after a previous infection from one of several botnets frequently leveraged in the cyber-criminal underground.

Impact

The malware has the ability to find and encrypt files located within shared network drives, USB drives, external hard drives, network file shares and even some cloud storage drives.  If one computer on a network becomes infected, mapped network drives could also become infected. CryptoLocker then connects to the attackers’ command and control (C2) server to deposit the asymmetric private encryption key out of the victim’s reach.

Victim files are encrypted using asymmetric encryption. Asymmetric encryption uses two different keys for encrypting and decrypting messages. Asymmetric encryption is a more secure form of encryption as only one party is aware of the private key, while both sides know the public key.

While victims are told they have three days to pay the attacker through a third-party payment method (MoneyPak, Bitcoin), some victims have claimed online that they paid the attackers and did not receive the promised decryption key.  US-CERT and DHS encourage users and administrators experiencing a ransomware infection to report the incident to the FBI at the Internet Crime Complaint Center (IC3).

Solution

Prevention

US-CERT recommends users and administrators take the following preventative measures to protect their computer networks from a CryptoLocker infection:

Mitigation

US-CERT suggests the following possible mitigation steps that users and administrators can implement, if you believe your computer has been infected with CryptoLocker malware:

  • Immediately disconnect the infected system from wireless or wired networks. This may prevent the malware from further encrypting any more files on the network.
  • Users who are infected with the malware should consult with a reputable security expert to assist in removing the malware.
  • If possible, change all online account passwords and network passwords after removing the system from the network. Change all system passwords once the malware is removed from the system.

References

Revisions

  • November 5, 2013: Initial Release
  • November 13, 2013: Update to Systems Affected (inclusion of Windows 8)
  • November 15, 2013: Updates to Impact and Prevention sections.
  • November 18, 2013: Updated Prevention and Mitigation Sections

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