Detection rules › Splunk
Proxy Execution via Appcert (PowerShell)
Threat actors may exploit legitimate developer utilities to execute malicious payloads by proxy. One such utility is appcert.exe, a command-line tool included in the Windows Application Certification Kit, which is typically used to verify the compliance of Windows applications with Microsoft's certification standards. This use case detects appcert executions with commands to proxy execution of another binary
MITRE ATT&CK coverage
| Tactic | Techniques |
|---|---|
| Execution | T1127 Trusted Developer Utilities Proxy Execution |
| Stealth | T1127 Trusted Developer Utilities Proxy Execution |
References
Event coverage
| Provider | Event | Title |
|---|---|---|
| PowerShell | Event ID 4103 | Payload Context: ContextInfo User Data: UserData. |
| PowerShell | Event ID 4104 | Creating Scriptblock text (MessageNumber of MessageTotal). |
Rule body yaml
id: '32821.58286'
title: Proxy Execution via Appcert
description: Threat actors may exploit legitimate developer utilities to execute malicious
payloads by proxy. One such utility is appcert.exe, a command-line tool included
in the Windows Application Certification Kit, which is typically used to verify
the compliance of Windows applications with Microsoft's certification standards.
This use case detects appcert executions with commands to proxy execution of another
binary. Living Off the Land Binary and Scripts (LOLBAS) (LOLBIN)
logic_format: Splunk
logic: '`get_endpoint_data` `get_endpoint_data_powershell` (TERM(EventCode=4103) OR
"<EventID>4103<" OR TERM(EventCode=4104) OR "<EventID>4104<") (TERM(appcert) OR
"appcert.exe") TERM(test) | regex process!="(?i)\-setupcommandline"| regex process="(?i)\stest\s"|
rex field=process "-setuppath\s+(?:\"|'')?(?<proxy_exec>[^\s\"'']+\.exe)(?:\"|'')?"
| table _time, host, user, process, proxy_exec | bin span=1s | stats values(*) as
* by _time, host '
techniques:
- defense-evasion:trusted developer utilities proxy execution
technique_id:
- T1127
data_category:
- PowerShell logs
references:
- https://attack.mitre.org/techniques/T1127/
- https://attack.mitre.org/techniques/T1218/007/
- https://lolbas-project.github.io/lolbas/OtherMSBinaries/Appcert/
Stages and Predicates
Stage 1: search
`get_endpoint_data` `get_endpoint_data_powershell` (TERM(EventCode=4103) OR "<EventID>4103<" OR TERM(EventCode=4104) OR "<EventID>4104<") (TERM(appcert) OR "appcert.exe") TERM(test)
Stage 2: regex
| regex process!="(?i)\-setupcommandline"
Stage 3: regex
| regex process="(?i)\stest\s"
Stage 4: rex
| rex field=process "-setuppath\s+(?:\"|')?(?<proxy_exec>[^\s\"']+\.exe)(?:\"|')?"
Stage 5: table
| table _time, host, user, process, proxy_exec
Stage 6: bucket
| bin span=1s
Stage 7: 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)\-setupcommandline" |
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>4103<" |
| 1 | TERM |
| 1 | "<EventID>4104<" |
| 1 | TERM |
| 1 | appcert |
| 1 | "appcert.exe" |
| 1 | TERM |
| 1 | test |