Suspicious Download from Office Domain

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

Detects suspicious ways to download files from Microsoft domains that are used to store attachments in Emails or OneNote documents

MITRE ATT&CK coverage

Tactic	Techniques
Resource Development	`T1608` Stage Capabilities
Command & Control	`T1105` Ingress Tool Transfer

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: Suspicious Download from Office Domain
id: 00d49ed5-4491-4271-a8db-650a4ef6f8c1
status: test
description: Detects suspicious ways to download files from Microsoft domains that are used to store attachments in Emails or OneNote documents
references:
    - https://twitter.com/an0n_r0/status/1474698356635193346?s=12
    - https://twitter.com/mrd0x/status/1475085452784844803?s=12
author: Florian Roth (Nextron Systems), Nasreddine Bencherchali (Nextron Systems)
date: 2021-12-27
modified: 2022-08-02
tags:
    - attack.command-and-control
    - attack.resource-development
    - attack.t1105
    - attack.t1608
logsource:
    product: windows
    category: process_creation
detection:
    selection_download:
        - Image|endswith:
              - '\curl.exe'
              - '\wget.exe'
        - CommandLine|contains:
              - 'Invoke-WebRequest'
              - 'iwr '
              - 'curl '
              - 'wget '
              - 'Start-BitsTransfer'
              - '.DownloadFile('
              - '.DownloadString('
    selection_domains:
        CommandLine|contains:
            - 'https://attachment.outlook.live.net/owa/'
            - 'https://onenoteonlinesync.onenote.com/onenoteonlinesync/'
    condition: all of selection_*
falsepositives:
    - Scripts or tools that download attachments from these domains (OneNote, Outlook 365)
level: high

Stages and Predicates

Stage 0: `condition`

all of selection_*

Stage 1: `selection_download`

selection_download:
    - Image|endswith:
          - '\curl.exe'
          - '\wget.exe'
    - CommandLine|contains:
          - 'Invoke-WebRequest'
          - 'iwr '
          - 'curl '
          - 'wget '
          - 'Start-BitsTransfer'
          - '.DownloadFile('
          - '.DownloadString('

Stage 2: `selection_domains`

selection_domains:
    CommandLine|contains:
        - 'https://attachment.outlook.live.net/owa/'
        - 'https://onenoteonlinesync.onenote.com/onenoteonlinesync/'

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	`.DownloadFile(` corpus 8 (sigma 7, chronicle 1) `.DownloadString(` corpus 8 (sigma 7, chronicle 1) `Invoke-WebRequest` corpus 13 (sigma 10, elastic 1, chronicle 1, kusto 1) `Start-BitsTransfer` corpus 4 (sigma 3, splunk 1) `curl` corpus 12 (sigma 11, chronicle 1) `https://attachment.outlook.live.net/owa/` `https://onenoteonlinesync.onenote.com/onenoteonlinesync/` `iwr` corpus 13 (sigma 11, chronicle 2) `wget` corpus 8 (sigma 7, chronicle 1)
`Image`	ends_with	`\curl.exe` corpus 30 (sigma 30) `\wget.exe` corpus 9 (sigma 9)

`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)

Suspicious Download from Office Domain

MITRE ATT&CK coverage

Event coverage

Rule body yaml

Stages and Predicates

Stage 0: `condition`

Stage 1: `selection_download`

Stage 2: `selection_domains`

Indicators

Keyboard shortcuts

Search operators

Suspicious Download from Office Domain

MITRE ATT&CK coverage

Event coverage

Rule body yaml

Stages and Predicates

Stage 0: condition

Stage 1: selection_download

Stage 2: selection_domains

Indicators

Stage 0: `condition`

Stage 1: `selection_download`

Stage 2: `selection_domains`