Suspicious Greedy Compression Using Rar.EXE

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

Detects RAR usage that creates an archive from a suspicious folder, either a system folder or one of the folders often used by attackers for staging purposes

MITRE ATT&CK coverage

Tactic	Techniques
Execution	`T1059` Command and Scripting Interpreter

Event coverage

Provider	Event	Title
Sysmon	Event ID 1	Process creation

Rule body yaml

title: Suspicious Greedy Compression Using Rar.EXE
id: afe52666-401e-4a02-b4ff-5d128990b8cb
status: test
description: Detects RAR usage that creates an archive from a suspicious folder, either a system folder or one of the folders often used by attackers for staging purposes
references:
    - https://decoded.avast.io/martinchlumecky/png-steganography
author: X__Junior (Nextron Systems), Florian Roth (Nextron Systems)
date: 2022-12-15
modified: 2024-01-02
tags:
    - attack.execution
    - attack.t1059
logsource:
    product: windows
    category: process_creation
detection:
    # Example : rar.exe a -m5 -r -y -ta20210204000000 -hp1qazxcde32ws -v2560k Asia1Dpt-PC-c.rar c:\\*.doc c:\\*.docx c:\\*.xls c:\\*.xlsx c:\\*.pdf c:\\*.ppt c:\\*.pptx c:\\*.jpg c:\\*.txt >nul
    selection_opt_1:
        - Image|endswith: '\rar.exe'
        - Description: 'Command line RAR'
    selection_opt_2:
        CommandLine|contains:
            - '.exe a '
            - ' a -m'
    selection_cli_flags:
        CommandLine|contains|all:
            - ' -hp' # password
            - ' -r ' # recursive
    selection_cli_folders:
        CommandLine|contains:
            - ' ?:\\\*.'
            - ' ?:\\\\\*.'
            - ' ?:\$Recycle.bin\'
            - ' ?:\PerfLogs\'
            - ' ?:\Temp'
            - ' ?:\Users\Public\'
            - ' ?:\Windows\'
            - ' %public%'
    condition: 1 of selection_opt_* and all of selection_cli_*
falsepositives:
    - Unknown
level: high

Stages and Predicates

Stage 0: `condition`

1 of selection_opt_* and all of selection_cli_*

Stage 1: `selection_opt_1`

selection_opt_1:
    - Image|endswith: '\rar.exe'
    - Description: 'Command line RAR'

Stage 2: `selection_opt_2`

selection_opt_2:
    CommandLine|contains:
        - '.exe a '
        - ' a -m'

Stage 3: `selection_cli_flags`

selection_cli_flags:
    CommandLine|contains|all:
        - ' -hp'
        - ' -r '

Stage 4: `selection_cli_folders`

selection_cli_folders:
    CommandLine|contains:
        - ' ?:\\\*.'
        - ' ?:\\\\\*.'
        - ' ?:\$Recycle.bin\'
        - ' ?:\PerfLogs\'
        - ' ?:\Temp'
        - ' ?:\Users\Public\'
        - ' ?:\Windows\'
        - ' %public%'

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	`%public%` `-hp` corpus 4 (sigma 4) `-r` corpus 10 (sigma 10) `?:\$Recycle.bin\` `?:\PerfLogs\` `?:\Temp` `?:\Users\Public\` `?:\Windows\` `?:\\\.` `?:\\\\\.` `a -m` `.exe a`
`Description`	eq	`Command line RAR` corpus 3 (sigma 3)
`Image`	ends_with	`\rar.exe` 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)

Suspicious Greedy Compression Using Rar.EXE

MITRE ATT&CK coverage

Event coverage

Rule body yaml

Stages and Predicates

Stage 0: `condition`

Stage 1: `selection_opt_1`

Stage 2: `selection_opt_2`

Stage 3: `selection_cli_flags`

Stage 4: `selection_cli_folders`

Indicators

Keyboard shortcuts

Search operators

Suspicious Greedy Compression Using Rar.EXE

MITRE ATT&CK coverage

Event coverage

Rule body yaml

Stages and Predicates

Stage 0: condition

Stage 1: selection_opt_1

Stage 2: selection_opt_2

Stage 3: selection_cli_flags

Stage 4: selection_cli_folders

Indicators

Stage 0: `condition`

Stage 1: `selection_opt_1`

Stage 2: `selection_opt_2`

Stage 3: `selection_cli_flags`

Stage 4: `selection_cli_folders`