Detection rules › Splunk
ngen.exe File Download (Sysmon)
ngen.exe (Native Image Generator) is a legitimate Windows binary that compiles .NET assemblies into native machine code to improve application performance. Threat actors can abuse ngen.exe to download files. This use case detects ngen.exe executions with commands to download a file from a remote location
MITRE ATT&CK coverage
| Tactic | Techniques |
|---|---|
| Command & Control | T1105 Ingress Tool Transfer |
References
Event coverage
| Provider | Event | Title |
|---|---|---|
| Sysmon | Event ID 1 | Process creation |
Rule body yaml
id: '35366.62197'
title: ngen.exe File Download
description: ngen.exe (Native Image Generator) is a legitimate Windows binary that
compiles .NET assemblies into native machine code to improve application performance.
Threat actors can abuse ngen.exe to download files. This use case detects ngen.exe
executions with commands to download a file from a remote location. Living Off the
Land Binary and Scripts (LOLBAS) (LOLBIN)
logic_format: Splunk
logic: '`get_endpoint_data` `get_endpoint_data_sysmon` (TERM(EventCode=1) OR "<EventID>1<")
"ngen.exe" | regex process_name="(?i)ngen\.exe"| regex process="(?i)ngen(\.exe(\"|\'')?)?\s+(\"|\'')?[A-Za-z0-9]{2,6}:\/\/[^\s]+"|
table _time, host, user, process, process_*, parent_* | bin span=1s | stats values(*)
as * by _time, host '
techniques:
- command-and-control:ingress tool transfer
technique_id:
- T1105
data_category:
- Windows Sysmon
references:
- https://lolbas-project.github.io/lolbas/Binaries/Ngen/
- https://attack.mitre.org/techniques/T1105/
- https://learn.microsoft.com/en-us/dotnet/framework/tools/ngen-exe-native-image-generator
Stages and Predicates
Stage 1: search
`get_endpoint_data` `get_endpoint_data_sysmon` (TERM(EventCode=1) OR "<EventID>1<") "ngen.exe"
Stage 2: regex
| regex process_name="(?i)ngen\.exe"
Stage 3: regex
| regex process="(?i)ngen(\.exe(\"|\')?)?\s+(\"|\')?[A-Za-z0-9]{2,6}:\/\/[^\s]+"
Stage 4: table
| table _time, host, user, process, process_*, parent_*
Stage 5: bucket
| bin span=1s
Stage 6: stats
| stats values(*) as * by _time, host
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.
| Field | Kind | Values |
|---|---|---|
EventCode | eq |
|
process | regex_match |
|
process_name | regex_match |
|
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>1<" |
| 1 | "ngen.exe" |