Detection rules › Splunk
Suspicious reCAPTCHA Command Line (Sysmon)
This use case detects commonly abused LOLBAS utilities referencing reCAPTCHA in the command line.
MITRE ATT&CK coverage
| Tactic | Techniques |
|---|---|
| Execution | T1059 Command and Scripting Interpreter |
| Stealth | T1218 System Binary Proxy Execution |
References
Event coverage
| Provider | Event | Title |
|---|---|---|
| Sysmon | Event ID 1 | Process creation |
Rule body yaml
id: '41487.76907'
title: Suspicious reCAPTCHA Command Line
description: This use case detects commonly abused LOLBAS utilities referencing reCAPTCHA
in the command line.
logic_format: Splunk
logic: '`get_endpoint_data` `get_endpoint_data_sysmon` (TERM(EventCode=1) OR "<EventID>1<")
("powershell.exe" OR "pwsh.exe" OR "cmd.exe" OR "services.exe" OR "dllhost.exe"
OR "rundll32.exe" OR "cscript.exe" OR "wscript.exe" OR "mshta.exe" OR "regsvr32.exe")
(TERM(reCAPTCHA) OR TERM(robot) OR TERM(human)) | regex process_path="(?i)(powershell|pwsh|cmd|services|dllhost|rundll32|mshta|regsvr32|cscript|wscript)\.exe"|
where match(process, "(?i)\sreCAPTCHA\s|I\s+am\s+not\s+a\s+robot|Verify\s+you\s+are\s+human")
or match(parent_process, "(?i)\sreCAPTCHA\s|I\s+am\s+not\s+a\s+robot|Verify\s+you\s+are\s+human")
| table _time, host, user parent_*, process_*, process| search `apply_al(AVL_R76907`|
bin span=1s | stats values(*) as * by _time, host '
techniques:
- defense-evasion:system binary proxy execution
- execution:command and scripting interpreter
technique_id:
- T1218
- T1059
data_category:
- Windows Sysmon
references:
- https://www.reliaquest.com/blog/using-captcha-for-compromise/
- https://www.netskope.com/blog/lumma-stealer-fake-captchas-new-techniques-to-evade-detection
Stages and Predicates
Stage 1: search
`get_endpoint_data` `get_endpoint_data_sysmon` (TERM(EventCode=1) OR "<EventID>1<") ("powershell.exe" OR "pwsh.exe" OR "cmd.exe" OR "services.exe" OR "dllhost.exe" OR "rundll32.exe" OR "cscript.exe" OR "wscript.exe" OR "mshta.exe" OR "regsvr32.exe") (TERM(reCAPTCHA) OR TERM(robot) OR TERM(human))
Stage 2: regex
| regex process_path="(?i)(powershell|pwsh|cmd|services|dllhost|rundll32|mshta|regsvr32|cscript|wscript)\.exe"
Stage 3: where
| where match(process, "(?i)\sreCAPTCHA\s|I\s+am\s+not\s+a\s+robot|Verify\s+you\s+are\s+human") or match(parent_process, "(?i)\sreCAPTCHA\s|I\s+am\s+not\s+a\s+robot|Verify\s+you\s+are\s+human")
Stage 4: table
| table _time, host, user parent_*, process_*, process
Stage 5: search
| search `apply_al(AVL_R76907`
Stage 6: bucket
| bin span=1s
Stage 7: 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 |
|
parent_process | match |
|
process | match |
|
process_path | 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 | "powershell.exe" |
| 1 | "pwsh.exe" |
| 1 | "cmd.exe" |
| 1 | "services.exe" |
| 1 | "dllhost.exe" |
| 1 | "rundll32.exe" |
| 1 | "cscript.exe" |
| 1 | "wscript.exe" |
| 1 | "mshta.exe" |
| 1 | "regsvr32.exe" |
| 1 | TERM |
| 1 | reCAPTCHA |
| 1 | TERM |
| 1 | robot |
| 1 | TERM |
| 1 | human |