Detection rules › Splunk
PowerShell DownloadFile_DownloadString (Windows Event Log)
Adversaries have the capability to move tools or files from an external system into a compromised environment. This involves copying tools or files from an external system controlled by the adversary to the victim network through the command and control channel. This use case detects PowerShell commands related to file downloads using DownloadFile and DownloadString methods. Executions involving Invoke-WebRequest and Invoke-Expression have been excluded as they are covered by other use cases.
MITRE ATT&CK coverage
| Tactic | Techniques |
|---|---|
| Execution | T1059.001 Command and Scripting Interpreter: PowerShell |
| Command & Control | T1105 Ingress Tool Transfer |
References
Event coverage
| Provider | Event | Title |
|---|---|---|
| Security-Auditing | Event ID 4688 | A new process has been created. |
Rule body yaml
id: '29435.53027'
title: PowerShell DownloadFile_DownloadString
description: Adversaries have the capability to move tools or files from an external
system into a compromised environment. This involves copying tools or files from
an external system controlled by the adversary to the victim network through the
command and control channel. This use case detects PowerShell commands related to
file downloads using DownloadFile and DownloadString methods. Executions involving
Invoke-WebRequest and Invoke-Expression have been excluded as they are covered by
other use cases.
logic_format: Splunk
logic: '`get_endpoint_data` `get_endpoint_data_winevent` (TERM(EventCode=4688) OR
"<EventID>4688<" OR Type=Process) ("downloadfile" OR "downloadstring") "System.Net.WebClient"
NOT ("Invoke-WebRequest" OR "Invoke-Expression") | regex process="(?i)System\.Net\.WebClient.+\.Download(file|string)"|
regex process!="(?i)(^|\s|\;|\|)(iex|iwr)(\s|\;|\|)"| table _time, host, user, process,
process_name, parent_process_name | bin span=1s | stats values(*) as * by _time,
host '
techniques:
- execution:command and scripting interpreter:powershell
- execution:command and scripting interpreter
- command-and-control:ingress tool transfer
technique_id:
- T1059.001
- T1059
- T1105
data_category:
- Process command-line parameters
- Windows event logs
references:
- https://blog.talosintelligence.com/lazarus-three-rats/
- https://blog.talosintelligence.com/prometei-botnet-improves/
Stages and Predicates
Stage 1: search
`get_endpoint_data` `get_endpoint_data_winevent` (TERM(EventCode=4688) OR "<EventID>4688<" OR Type=Process) ("downloadfile" OR "downloadstring") "System.Net.WebClient" NOT ("Invoke-WebRequest" OR "Invoke-Expression")
Stage 2: regex
| regex process="(?i)System\.Net\.WebClient.+\.Download(file|string)"
Stage 3: regex
| regex process!="(?i)(^|\s|\;|\|)(iex|iwr)(\s|\;|\|)"
Stage 4: table
| table _time, host, user, process, process_name, parent_process_name
Stage 5: bucket
| bin span=1s
Stage 6: stats
| stats values(*) as * by _time, host
Exclusions
Top-level NOT(...) conjuncts: predicates this rule actively suppresses.
| Field | Kind | Excluded values |
|---|---|---|
process | regex_match | "(?i)(^|\s|\;||)(iex|iwr)(\s|\;||)" |
Indicators
Each row is a field, operator, and value that the rule matches. The corpus column counts how many other rules in the catalog look for the same combination: high numbers point to widely-used, community-vetted indicators. Blank or 1 shows that the indicator is specific to this rule.
Search terms
Bare-string tokens in the SPL search body. Splunk matches each token against _raw (the untyped raw event text) anywhere it appears, not against a specific field. These don't surface in the Indicators table because they aren't predicates on a known field.
| Stage | Term |
|---|---|
| 1 | TERM |
| 1 | "<EventID>4688<" |
| 1 | "downloadfile" |
| 1 | "downloadstring" |
| 1 | "System.Net.WebClient" |
| 1 | "Invoke-WebRequest" |
| 1 | "Invoke-Expression" |