Detection rules › Splunk
Visual Studio Code Tunnel Execution (Sysmon)
Adversaries may communicate using application layer protocols associated with web traffic to avoid detection/network filtering by blending in with existing traffic. Commands to the remote system, and often the results of those commands, will be embedded within the protocol traffic between the client and server. This use case detects the execution of Visual Studio Code tunnel in attempt to establish a C2 channel, accounting for instances where the binary has been renamed.
MITRE ATT&CK coverage
| Tactic | Techniques |
|---|---|
| Command & Control | T1071.001 Application Layer Protocol: Web Protocols |
References
Event coverage
| Provider | Event | Title |
|---|---|---|
| Sysmon | Event ID 1 | Process creation |
Rule body yaml
id: '40420.73844'
title: Visual Studio Code Tunnel Execution
description: Adversaries may communicate using application layer protocols associated
with web traffic to avoid detection/network filtering by blending in with existing
traffic. Commands to the remote system, and often the results of those commands,
will be embedded within the protocol traffic between the client and server. This
use case detects the execution of Visual Studio Code tunnel in attempt to establish
a C2 channel, accounting for instances where the binary has been renamed.
logic_format: Splunk
logic: ' `get_endpoint_data` `get_endpoint_data_sysmon` (TERM(EventCode=1) OR "<EventID>1<")
(".exe" "tunnel") OR (".exe" "tunnel" "--name " "--accept-server-license-terms")
OR (" tunnel" "cmd.exe" "/d" "/c" "\servers\Stable-" "code-server.cmd") | where
match(process, "(?i)\.exe\s+tunnel$") or (match(process, "(?i)\.exe\s+tunnel") and
match(process, "(?i)--name\s+") and match(process, "(?i)--accept-server-license-terms"))
or (match(parent_process, "(?i)\stunnel$") and match(process_name, "(?i)cmd\.exe")
and match(process, "\s/d\s") and match(process, "\s/c\s") and match(process, "(?i)\x5cservers\x5cStable-")
and match(process, "(?i)code-server\.cmd")) | table _time, host, user, process,
process_*, parent_* | bin span=1s | stats values(*) as * by _time, host '
techniques:
- command-and-control:application layer protocol:web protocols
technique_id:
- T1071.001
data_category:
- Windows Sysmon
references:
- https://detection.fyi/sigmahq/sigma/windows/process_creation/proc_creation_win_vscode_tunnel_execution/
- https://attack.mitre.org/techniques/T1071/001/
- https://www.sentinelone.com/labs/operation-digital-eye-chinese-apt-compromises-critical-digital-infrastructure-via-visual-studio-code-tunnels/
Stages and Predicates
Stage 1: search
`get_endpoint_data` `get_endpoint_data_sysmon` (TERM(EventCode=1) OR "<EventID>1<") (".exe" "tunnel") OR (".exe" "tunnel" "--name " "--accept-server-license-terms") OR (" tunnel" "cmd.exe" "/d" "/c" "\servers\Stable-" "code-server.cmd")
Stage 2: where
| where match(process, "(?i)\.exe\s+tunnel$") or (match(process, "(?i)\.exe\s+tunnel") and match(process, "(?i)--name\s+") and match(process, "(?i)--accept-server-license-terms")) or (match(parent_process, "(?i)\stunnel$") and match(process_name, "(?i)cmd\.exe") and match(process, "\s/d\s") and match(process, "\s/c\s") and match(process, "(?i)\x5cservers\x5cStable-") and match(process, "(?i)code-server\.cmd"))
Stage 3: table
| table _time, host, user, process, process_*, parent_*
Stage 4: bucket
| bin span=1s
Stage 5: 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_name | 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 | ".exe" |
| 1 | "tunnel" |
| 1 | ".exe" |
| 1 | "tunnel" |
| 1 | "--name " |
| 1 | "--accept-server-license-terms" |
| 1 | " tunnel" |
| 1 | "cmd.exe" |
| 1 | "/d" |
| 1 | "/c" |
| 1 | "\servers\Stable-" |
| 1 | "code-server.cmd" |