Communication To Ngrok Tunneling Service Initiated

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

Detects an executable initiating a network connection to "ngrok" tunneling domains. Attackers were seen using this "ngrok" in order to store their second stage payloads and malware. While communication with such domains can be legitimate, often times is a sign of either data exfiltration by malicious actors or additional download.

MITRE ATT&CK coverage

Tactic	Techniques
Command & Control	`T1090` Proxy, `T1102` Web Service, `T1568.002` Dynamic Resolution: Domain Generation Algorithms, `T1572` Protocol Tunneling
Exfiltration	`T1567` Exfiltration Over Web Service

Event coverage

Provider	Event	Title
Sysmon	Event ID 3	Network connection

Rule body yaml

title: Communication To Ngrok Tunneling Service Initiated
id: 1d08ac94-400d-4469-a82f-daee9a908849
related:
    - id: 18249279-932f-45e2-b37a-8925f2597670
      type: similar
status: test
description: |
    Detects an executable initiating a network connection to "ngrok" tunneling domains.
    Attackers were seen using this "ngrok" in order to store their second stage payloads and malware.
    While communication with such domains can be legitimate, often times is a sign of either data exfiltration by malicious actors or additional download.
references:
    - https://twitter.com/hakluke/status/1587733971814977537/photo/1
    - https://ngrok.com/docs/secure-tunnels/tunnels/ssh-reverse-tunnel-agent
author: Florian Roth (Nextron Systems)
date: 2022-11-03
modified: 2024-02-02
tags:
    - attack.exfiltration
    - attack.command-and-control
    - attack.t1567
    - attack.t1568.002
    - attack.t1572
    - attack.t1090
    - attack.t1102
    - attack.s0508
logsource:
    category: network_connection
    product: windows
detection:
    selection:
        DestinationHostname|contains:
            - 'tunnel.us.ngrok.com'
            - 'tunnel.eu.ngrok.com'
            - 'tunnel.ap.ngrok.com'
            - 'tunnel.au.ngrok.com'
            - 'tunnel.sa.ngrok.com'
            - 'tunnel.jp.ngrok.com'
            - 'tunnel.in.ngrok.com'
    condition: selection
falsepositives:
    - Legitimate use of the ngrok service.
level: high

Stages and Predicates

Stage 0: `condition`

selection

Stage 1: `selection`

selection:
    DestinationHostname|contains:
        - 'tunnel.us.ngrok.com'
        - 'tunnel.eu.ngrok.com'
        - 'tunnel.ap.ngrok.com'
        - 'tunnel.au.ngrok.com'
        - 'tunnel.sa.ngrok.com'
        - 'tunnel.jp.ngrok.com'
        - 'tunnel.in.ngrok.com'

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
`DestinationHostname`	match	`tunnel.ap.ngrok.com` corpus 2 (sigma 2) `tunnel.au.ngrok.com` corpus 2 (sigma 2) `tunnel.eu.ngrok.com` corpus 2 (sigma 2) `tunnel.in.ngrok.com` corpus 2 (sigma 2) `tunnel.jp.ngrok.com` corpus 2 (sigma 2) `tunnel.sa.ngrok.com` corpus 2 (sigma 2) `tunnel.us.ngrok.com` corpus 2 (sigma 2)

`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)

Communication To Ngrok Tunneling Service Initiated

MITRE ATT&CK coverage

Event coverage

Rule body yaml

Stages and Predicates

Stage 0: `condition`

Stage 1: `selection`

Indicators

Keyboard shortcuts

Search operators

Communication To Ngrok Tunneling Service Initiated

MITRE ATT&CK coverage

Event coverage

Rule body yaml

Stages and Predicates

Stage 0: condition

Stage 1: selection

Indicators

Stage 0: `condition`

Stage 1: `selection`