SUNBURST Command and Control Activity

## Triage and analysis

### Investigating SUNBURST Command and Control Activity

SUNBURST is a trojanized version of a digitally signed SolarWinds Orion plugin called
SolarWinds.Orion.Core.BusinessLayer.dll. The plugin contains a backdoor that communicates via HTTP to third-party
servers. After an initial dormant period of up to two weeks, SUNBURST may retrieve and execute commands that instruct
the backdoor to transfer files, execute files, profile the system, reboot the system, and disable system services.
The malware's network traffic attempts to blend in with legitimate SolarWinds activity by imitating the Orion
Improvement Program (OIP) protocol, and the malware stores persistent state data within legitimate plugin configuration files. The
backdoor uses multiple obfuscated blocklists to identify processes, services, and drivers associated with forensic and
anti-virus tools.

More details on SUNBURST can be found on the [Mandiant Report](https://www.mandiant.com/resources/sunburst-additional-technical-details).

This rule identifies suspicious network connections that attempt to blend in with legitimate SolarWinds activity
by imitating the Orion Improvement Program (OIP) protocol behavior.

#### Possible investigation steps

- Investigate the process execution chain (parent process tree) for unknown processes. Examine their executable files
for prevalence, whether they are located in expected locations, and if they are signed with valid digital signatures.
- Retrieve the executable involved:
  - Use a private sandboxed malware analysis system to perform analysis.
    - Observe and collect information about the following activities:
      - Attempts to contact external domains and addresses.
      - File and registry access, modification, and creation activities.
      - Service creation and launch activities.
      - Scheduled tasks creation.
  - Use the PowerShell Get-FileHash cmdlet to get the files' SHA-256 hash values.
    - Search for the existence and reputation of the hashes in resources like VirusTotal, Hybrid-Analysis, CISCO Talos, Any.run, etc.
- Investigate whether the potential malware ran successfully, is active on the host, or was stopped by defenses.
- Investigate the network traffic.
- Investigate other alerts associated with the user/host during the past 48 hours.

### False positive analysis

- This activity should not happen legitimately. The security team should address any potential benign true positive
(B-TP), as this configuration can put the environment at risk.

### Response and remediation

- Initiate the incident response process based on the outcome of the triage.
- Isolate the involved host to prevent further post-compromise behavior.
- If the triage identified malware, search the environment for additional compromised hosts.
  - Implement temporary network rules, procedures, and segmentation to contain the malware.
  - Stop suspicious processes.
  - Immediately block the identified indicators of compromise (IoCs).
  - Inspect the affected systems for additional malware backdoors like reverse shells, reverse proxies, or droppers that
  attackers could use to reinfect the system.
- Remove and block malicious artifacts identified during triage.
- Run a full antimalware scan. This may reveal additional artifacts left in the system, persistence mechanisms, and
malware components.
- Reimage the host operating system and restore compromised files to clean versions.
- Upgrade SolarWinds systems to the latest version to eradicate the chance of reinfection by abusing the same vector.
- Using the incident response data, update logging and audit policies to improve the mean time to detect (MTTD) and the
mean time to respond (MTTR).