PUA - Ngrok Execution

Status: test
Severity: high
Log source: product windows, category process_creation
Author: Florian Roth (Nextron Systems)
Source: github.com/SigmaHQ/sigma

Detects the use of Ngrok, a utility used for port forwarding and tunneling, often used by threat actors to make local protected services publicly available. Involved domains are bin.equinox.io for download and *.ngrok.io for connections.

MITRE ATT&CK coverage

Tactic	Techniques
Command & Control	`T1572` Protocol Tunneling

Event coverage

Provider	Event	Title
Sysmon	Event ID 1	Process creation
Security-Auditing	Event ID 4688	A new process has been created.

Rule body yaml

title: PUA - Ngrok Execution
id: ee37eb7c-a4e7-4cd5-8fa4-efa27f1c3f31
status: test
description: |
  Detects the use of Ngrok, a utility used for port forwarding and tunneling, often used by threat actors to make local protected services publicly available.
  Involved domains are bin.equinox.io for download and *.ngrok.io for connections.
references:
    - https://ngrok.com/docs
    - https://www.fireeye.com/blog/threat-research/2021/05/shining-a-light-on-darkside-ransomware-operations.html
    - https://stackoverflow.com/questions/42442320/ssh-tunnel-to-ngrok-and-initiate-rdp
    - https://www.virustotal.com/gui/file/58d21840d915aaf4040ceb89522396124c82f325282f805d1085527e1e2ccfa1/detection
    - https://cybleinc.com/2021/02/15/ngrok-platform-abused-by-hackers-to-deliver-a-new-wave-of-phishing-attacks/
    - https://twitter.com/xorJosh/status/1598646907802451969
    - https://www.softwaretestinghelp.com/how-to-use-ngrok/
author: Florian Roth (Nextron Systems)
date: 2021-05-14
modified: 2023-02-21
tags:
    - attack.command-and-control
    - attack.t1572
logsource:
    category: process_creation
    product: windows
detection:
    selection1:
        CommandLine|contains:
            - ' tcp 139'
            - ' tcp 445'
            - ' tcp 3389'
            - ' tcp 5985'
            - ' tcp 5986'
    selection2:
        CommandLine|contains|all:
            - ' start '
            - '--all'
            - '--config'
            - '.yml'
    selection3:
        Image|endswith: 'ngrok.exe'
        CommandLine|contains:
            - ' tcp '
            - ' http '
            - ' authtoken '
    selection4:
        CommandLine|contains:
            - '.exe authtoken '
            - '.exe start --all'
    condition: 1 of selection*
falsepositives:
    - Another tool that uses the command line switches of Ngrok
    - Ngrok http 3978 (https://learn.microsoft.com/en-us/azure/bot-service/bot-service-debug-channel-ngrok?view=azure-bot-service-4.0)
level: high

Stages and Predicates

Stage 0: `condition`

1 of selection*

Stage 1: `selection1`

selection1:
    CommandLine|contains:
        - ' tcp 139'
        - ' tcp 445'
        - ' tcp 3389'
        - ' tcp 5985'
        - ' tcp 5986'

Stage 2: `selection2`

selection2:
    CommandLine|contains|all:
        - ' start '
        - '--all'
        - '--config'
        - '.yml'

Stage 3: `selection3`

selection3:
    Image|endswith: 'ngrok.exe'
    CommandLine|contains:
        - ' tcp '
        - ' http '
        - ' authtoken '

Stage 4: `selection4`

selection4:
    CommandLine|contains:
        - '.exe authtoken '
        - '.exe start --all'

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
`CommandLine`	match	`authtoken` `http` `start` corpus 2 (sigma 2) `tcp` `tcp 139` `tcp 3389` `tcp 445` `tcp 5985` `tcp 5986` `--all` `--config` `.exe authtoken` `.exe start --all` `.yml` corpus 2 (sigma 2)
`Image`	ends_with	`ngrok.exe`

`j` / `k`	Scroll down / up
`d` / `u`	Half-page down / up
`gg` / `G`	Top / bottom
`h` / `l`	History back / forward
`f`	Follow link (`Shift` = new tab)
`/`	Focus search
`?`	Toggle this help
`↑` / `↓`	Navigate search results
`Enter`	Open highlighted result
`Esc`	Close results / dialog

`type:`	`events` / `rules` / `providers`
`vendor:`	`sigma` / `elastic` / `splunk` / `kusto` / `chronicle` (vendor name alone also works: `sigma:`, `kql:`, `secops:`…)
`tactic:`	TA-id, slug, or name: `credential_access`, `TA0006`
`technique:`	technique or sub-technique ID: `T1003`, `T1003.001` (alias `tech:`)
`severity:`	`critical` / `high` / `medium` / `low` / `informational` (alias `sev:`)
`risk_score`	Numeric comparison on the Elastic risk score (0 to 100): `risk_score>50`, `risk_score<=20`, `risk_score=99` (alias `risk`; Elastic rules only)
`stages:`	Rules with exactly N pipeline stages
`correlation:`	`single_event` / `sequence` / `alternatives` / `alternatives_cross_log` / `all_required` / `correlated`
`with:`	Co-occurrence event-id; stacks (`with:4624 with:4769`) to require all, while a comma list in one occurrence (`with:4624,4769`) is an either-or group. Implies multi-event
`like:`	Structural neighbors of a rule slug (equivalents + subsumption stricter / broader): `like:comsvcs_lsass_memory_dump-splunk-sysmon`
`groupby:`	Entity-grouping substring match against `group_by_keys`: `groupby:user`, `groupby:host`
`uses:`	Rules whose predicate tree touches the field (any kind, any value): `uses:CommandLine`
`excludes:`	Rules with top-level `not()` clauses on the field (FP whitelists): `excludes:ParentImage`
`field:` / `value:`	Predicate search; narrows rule cards to those with a matching leaf and drives the indicator tier. Unquoted = substring, wildcards allowed (`value:mimikatz`)
`indicator:`	Shorthand for `field:F value:V`: `indicator:Image=*\powershell.exe`
`kind:`	Filter by predicate kind. Narrows rule cards to those carrying a matching predicate leaf (`vendor:elastic kind:cidr_match`) and drives the indicator tier: `contains` / `starts_with` / `ends_with` / `regex` / `cidr` / `eq` / `in` … (operator aliases `op:`/`match:`)
`has:` / `no:`	`sample`, `field`, `notes`, `refs`, `trace`, `thirdparty`, `rule`, `pattern`, `timewindow`, `threshold`, `newterms`, `sigma`/`elastic`/`splunk`/`kusto`/`chronicle`
`-op:val`	Exclude matches; works on most operators but not `type:`/`like:`/`has:`/`no:` (use `no:<flag>` to exclude a rule flag): `tactic:execution -vendor:splunk`. Standalone `-kind:`/`-field:`/`-value:` drop every rule carrying a matching predicate leaf (`type:rules -kind:is_null`)
`field:"…"` / `value:"…"`	Quoted value = anchored exact match (also allows spaces): `value:"net user"`
`a,b`	Comma = OR inside one operator (`vendor:sigma,elastic`, `severity:high,critical`); repeating a facet merges the same way. `field:`/`value:` never split (literal commas)
`vendors:` / `stage:`	Singular and plural spellings fold to the canonical operator and value: `tactics:` = `tactic:`, `type:event` = `type:events`, `correlation:sequences` = `correlation:sequence`, `has:thresholds` = `has:threshold`
`"quoted phrase"`	Exact-match a multi-word phrase (free text)

PUA - Ngrok Execution

MITRE ATT&CK coverage

Event coverage

Rule body yaml

Stages and Predicates

Stage 0: `condition`

Stage 1: `selection1`

Stage 2: `selection2`

Stage 3: `selection3`

Stage 4: `selection4`

Indicators

Keyboard shortcuts

Search operators

PUA - Ngrok Execution

MITRE ATT&CK coverage

Event coverage

Rule body yaml

Stages and Predicates

Stage 0: condition

Stage 1: selection1

Stage 2: selection2

Stage 3: selection3

Stage 4: selection4

Indicators

Stage 0: `condition`

Stage 1: `selection1`

Stage 2: `selection2`

Stage 3: `selection3`

Stage 4: `selection4`