Download From Suspicious TLD - Whitelist

Status: test
Severity: low
Log source: category proxy
Author: Florian Roth (Nextron Systems)
Source: github.com/SigmaHQ/sigma

Detects executable downloads from suspicious remote systems

MITRE ATT&CK coverage

Tactic	Techniques
Initial Access	`T1566` Phishing
Execution	`T1203` Exploitation for Client Execution, `T1204.002` User Execution: Malicious File

Rule body yaml

title: Download From Suspicious TLD - Whitelist
id: b5de2919-b74a-4805-91a7-5049accbaefe
related:
    - id: 00d0b5ab-1f55-4120-8e83-487c0a7baf19
      type: similar
status: test
description: Detects executable downloads from suspicious remote systems
references:
    - Internal Research
author: Florian Roth (Nextron Systems)
date: 2017-03-13
modified: 2023-05-18
tags:
    - attack.initial-access
    - attack.t1566
    - attack.execution
    - attack.t1203
    - attack.t1204.002
logsource:
    category: proxy
detection:
    selection:
        c-uri-extension:
            - 'exe'
            - 'vbs'
            - 'bat'
            - 'rar'
            - 'ps1'
            - 'doc'
            - 'docm'
            - 'xls'
            - 'xlsm'
            - 'pptm'
            - 'rtf'
            - 'hta'
            - 'dll'
            - 'ws'
            - 'wsf'
            - 'sct'
            - 'zip'
            # If you want to add more extensions - see https://docs.google.com/spreadsheets/d/1TWS238xacAto-fLKh1n5uTsdijWdCEsGIM0Y0Hvmc5g/
    filter:
        cs-host|endswith:
            - '.com'
            - '.org'
            - '.net'
            - '.edu'
            - '.gov'
            - '.uk'
            - '.ca'
            - '.de'
            - '.jp'
            - '.fr'
            - '.au'
            - '.us'
            - '.ch'
            - '.it'
            - '.nl'
            - '.se'
            - '.no'
            - '.es'
            # Extend this list as needed
    condition: selection and not filter
falsepositives:
    - All kind of software downloads
level: low

Stages and Predicates

Stage 0: `condition`

selection and not filter

Stage 1: `selection`

selection:
    c-uri-extension:
        - 'exe'
        - 'vbs'
        - 'bat'
        - 'rar'
        - 'ps1'
        - 'doc'
        - 'docm'
        - 'xls'
        - 'xlsm'
        - 'pptm'
        - 'rtf'
        - 'hta'
        - 'dll'
        - 'ws'
        - 'wsf'
        - 'sct'
        - 'zip'

Stage 2: `not filter`

filter:
    cs-host|endswith:
        - '.com'
        - '.org'
        - '.net'
        - '.edu'
        - '.gov'
        - '.uk'
        - '.ca'
        - '.de'
        - '.jp'
        - '.fr'
        - '.au'
        - '.us'
        - '.ch'
        - '.it'
        - '.nl'
        - '.se'
        - '.no'
        - '.es'

Exclusions

Top-level NOT(...) conjuncts: predicates this rule actively suppresses.

Field	Kind	Excluded values
`cs-host`	ends_with	`.au`
`cs-host`	ends_with	`.ca`
`cs-host`	ends_with	`.ch`
`cs-host`	ends_with	`.com`
`cs-host`	ends_with	`.de`
`cs-host`	ends_with	`.edu`
`cs-host`	ends_with	`.es`
`cs-host`	ends_with	`.fr`
`cs-host`	ends_with	`.gov`
`cs-host`	ends_with	`.it`
`cs-host`	ends_with	`.jp`
`cs-host`	ends_with	`.net`
`cs-host`	ends_with	`.nl`
`cs-host`	ends_with	`.no`
`cs-host`	ends_with	`.org`
`cs-host`	ends_with	`.se`
`cs-host`	ends_with	`.uk`
`cs-host`	ends_with	`.us`

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
`c-uri-extension`	eq	`bat` `dll` `doc` `docm` `exe` `hta` `pptm` `ps1` `rar` `rtf` `sct` `vbs` `ws` `wsf` `xls` `xlsm` `zip`

`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)

Download From Suspicious TLD - Whitelist

MITRE ATT&CK coverage

Rule body yaml

Stages and Predicates

Stage 0: `condition`

Stage 1: `selection`

Stage 2: `not filter`

Exclusions

Indicators

Keyboard shortcuts

Search operators

Download From Suspicious TLD - Whitelist

MITRE ATT&CK coverage

Rule body yaml

Stages and Predicates

Stage 0: condition

Stage 1: selection

Stage 2: not filter

Exclusions

Indicators

Stage 0: `condition`

Stage 1: `selection`

Stage 2: `not filter`