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CHAINSHOT Shellcode Downloader

A new malware campaign has been observed distributing CHAINSHOT, a downloader trojan, to organisations throughout Europe and the Middle East.
Threat ID:
CC-2658
Category:
Backdoor, Trojan
Threat Severity:
Medium
Threat Vector:
Phishing, Email spam
Published:
10 September 2018 12:00 AM
Report a cyber attack: call 0300 303 5222 or email [email protected]

This content has been archived

This article no longer conforms to NHS Digital's standards for cyber alerts, and may contain outdated or inaccurate information. Use of this information contained in this page is at your own risk

Summary

A new malware campaign has been observed distributing CHAINSHOT, a downloader trojan, to organisations throughout Europe and the Middle East.

Affected platforms

The following platforms are known to be affected:

Microsoft Windows

  • Microsoft Windows - All versions

Threat details

CHAINSHOT is delivered using a multi-stage infection vector. Initially, a Microsoft Excel attachment is delivered via spam or phishing email; this file contains a Shockwave Flash ActiveX object that directs to a URL. When the object is executed, an obfuscated Flash dropper is downloaded from the URL that creates a randomised 512-bit RSA key pair. The public key of this pair is sent to a command and control (C2) server, which uses it to encrypt the key for a 128-bit AES encrypted Flash exploit and secondary payload. These are then sent to the Flash dropper, which decrypts and executes the exploit and payload. The Flash exploit is used to gain administrative privileges for the secondary payload, which then loads the embedded CHAINSHOT DLL file.

Once installed, CHAINSHOT will search for several popular anti-virus tools and will attempt to bypass them, terminating itself if unable to do so. If successful, it will collect system and user information to send to the C2 server before injecting another DLL containing a shellcode module into a running process. This module is then used to retrieve final payloads, although at the time of publication it is unclear what these payloads may be.

For further information:

Remediation advice

To prevent and detect an infection, ensure that:

Remediation steps

Type Step
  • A robust program of education and awareness training is delivered to users to ensure they don’t open attachments or follow links within unsolicited emails.
  • All operating systems, anti-virus and other security products are kept up-to-date.
  • Regular anti-virus and security scans are performed on your organisation’s estate.
  • All day-to-day computer activities such as email and internet are performed using non-administrative accounts.
  • Strong password policies are in place.
  • Network, proxy and firewall logs should be monitored for suspicious activity.
  • User accounts accessed from affected devices should be reset on a clean computer.
  • Your organisation adopts a holistic all-round approach to Cyber Security as advocated by the 10 Steps to Cyber Security.

Last edited: 17 February 2020 12:39 pm