Potential Data Exfiltration Via Curl.EXE

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

Detects the execution of the "curl" process with "upload" flags. Which might indicate potential data exfiltration

MITRE ATT&CK coverage

Tactic	Techniques
Command & Control	`T1105` Ingress Tool Transfer
Exfiltration	`T1567` Exfiltration Over Web Service

Event coverage

Provider	Event	Title
Sysmon	Event ID 1	Process creation

Rule body yaml

title: Potential Data Exfiltration Via Curl.EXE
id: 00bca14a-df4e-4649-9054-3f2aa676bc04
status: test
description: Detects the execution of the "curl" process with "upload" flags. Which might indicate potential data exfiltration
references:
    - https://twitter.com/d1r4c/status/1279042657508081664
    - https://medium.com/@petehouston/upload-files-with-curl-93064dcccc76
    - https://github.com/redcanaryco/atomic-red-team/blob/f339e7da7d05f6057fdfcdd3742bfcf365fee2a9/atomics/T1105/T1105.md#atomic-test-19---curl-upload-file
    - https://curl.se/docs/manpage.html
author: Florian Roth (Nextron Systems), Cedric MAURUGEON (Update)
date: 2020-07-03
modified: 2023-05-02
tags:
    - attack.exfiltration
    - attack.command-and-control
    - attack.t1567
    - attack.t1105
    - detection.threat-hunting
logsource:
    category: process_creation
    product: windows
detection:
    selection_img:
        - Image|endswith: '\curl.exe'
        - Product: 'The curl executable'
    selection_cli:
        - CommandLine|contains:
              - ' --form' # Also covers the "--form-string"
              - ' --upload-file '
              - ' --data '
              - ' --data-' # For flags like: "--data-ascii", "--data-binary", "--data-raw", "--data-urlencode"
        - CommandLine|re: '\s-[FTd]\s' # We use regex to ensure a case sensitive argument detection
    filter_optional_localhost:
        CommandLine|contains:
            - '://localhost'
            - '://127.0.0.1'
    condition: all of selection_* and not 1 of filter_optional_*
falsepositives:
    - Scripts created by developers and admins
level: medium

Stages and Predicates

Stage 0: `condition`

all of selection_* and not 1 of filter_optional_*

Stage 1: `selection_img`

selection_img:
    - Image|endswith: '\curl.exe'
    - Product: 'The curl executable'

Stage 2: `selection_cli`

selection_cli:
    - CommandLine|contains:
          - ' --form'
          - ' --upload-file '
          - ' --data '
          - ' --data-'
    - CommandLine|re: '\s-[FTd]\s'

Stage 3: `not filter_optional_localhost`

filter_optional_localhost:
    CommandLine|contains:
        - '://localhost'
        - '://127.0.0.1'

Exclusions

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

Field	Kind	Excluded values
`CommandLine`	match	`://127.0.0.1`
`CommandLine`	match	`://localhost`

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	`--data` corpus 3 (sigma 3) `--data-` corpus 2 (sigma 2) `--form` corpus 2 (sigma 2) `--upload-file` corpus 2 (sigma 2)
`CommandLine`	regex_match	`\s-[FTd]\s` corpus 2 (sigma 2)
`Image`	ends_with	`\curl.exe` corpus 30 (sigma 30)
`Product`	eq	`The curl executable` corpus 5 (sigma 5)

`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)

Potential Data Exfiltration Via Curl.EXE

MITRE ATT&CK coverage

Event coverage

Rule body yaml

Stages and Predicates

Stage 0: `condition`

Stage 1: `selection_img`

Stage 2: `selection_cli`

Stage 3: `not filter_optional_localhost`

Exclusions

Indicators

Keyboard shortcuts

Search operators

Potential Data Exfiltration Via Curl.EXE

MITRE ATT&CK coverage

Event coverage

Rule body yaml

Stages and Predicates

Stage 0: condition

Stage 1: selection_img

Stage 2: selection_cli

Stage 3: not filter_optional_localhost

Exclusions

Indicators

Stage 0: `condition`

Stage 1: `selection_img`

Stage 2: `selection_cli`

Stage 3: `not filter_optional_localhost`