Detection rules › Splunk
Unusual AppCert Child Process (Windows Event Log)
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 launching child processes outside of known good paths C:\Program Files\Windows Kits\10\App Certification Kit\ and C:\Program Files (x86)\Windows Kits\10\App Certification Kit\
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 |
|---|---|---|
| Security-Auditing | Event ID 4688 | A new process has been created. |
Rule body yaml
id: '35215.61886'
title: Unusual AppCert Child Process
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 launching child processes outside of known good paths
C:\Program Files\Windows Kits\10\App Certification Kit\ and C:\Program Files (x86)\Windows
Kits\10\App Certification Kit\. Living Off the Land Binary and Scripts (LOLBAS)
(LOLBIN)
logic_format: Splunk
logic: '`get_endpoint_data` `get_endpoint_data_winevent` (TERM(EventCode=4688) OR
"<EventID>4688<" OR Type=Process) (TERM(appcert) OR "appcert.exe") | regex parent_process_name="(?i)^appcert.exe"|
regex process_path!="(?i)\x5cProgram\sFiles(\s\(x86\))?\x5cWindows\sKits\x5c10\x5c"
| table _time, host, user, process, signature_id, parent_process_*, process_* |
bin span=1s | stats values(*) as * by _time, host '
techniques:
- defense-evasion:trusted developer utilities proxy execution
technique_id:
- T1127
data_category:
- Windows event 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_winevent` (TERM(EventCode=4688) OR "<EventID>4688<" OR Type=Process) (TERM(appcert) OR "appcert.exe")
Stage 2: regex
| regex parent_process_name="(?i)^appcert.exe"
Stage 3: regex
| regex process_path!="(?i)\x5cProgram\sFiles(\s\(x86\))?\x5cWindows\sKits\x5c10\x5c"
Stage 4: table
| table _time, host, user, process, signature_id, parent_process_*, process_*
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_path | regex_match | "(?i)\x5cProgram\sFiles(\s(x86))?\x5cWindows\sKits\x5c10\x5c" |
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 |
|
parent_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>4688<" |
| 1 | TERM |
| 1 | appcert |
| 1 | "appcert.exe" |