Writing Of Malicious Files To The Fonts Folder

Status: test
Severity: medium
Log source: product windows, category process_creation
Author: Sreeman
Source: github.com/SigmaHQ/sigma

Monitors for the hiding possible malicious files in the C:\Windows\Fonts\ location. This folder doesn't require admin privillege to be written and executed from.

MITRE ATT&CK coverage

Tactic	Techniques
Execution	`T1059` Command and Scripting Interpreter
Stealth	`T1211` Exploitation for Stealth

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: Writing Of Malicious Files To The Fonts Folder
id: ae9b0bd7-8888-4606-b444-0ed7410cb728
status: test
description: Monitors for the hiding possible malicious files in the C:\Windows\Fonts\ location. This folder doesn't require admin privillege to be written and executed from.
references:
    - https://thedfirreport.com/2020/04/20/sqlserver-or-the-miner-in-the-basement/
author: Sreeman
date: 2020-04-21
modified: 2022-03-08
tags:
    - attack.stealth
    - attack.t1211
    - attack.t1059
    - attack.persistence
    - attack.execution
logsource:
    product: windows
    category: process_creation
detection:
    selection_1:
        CommandLine|contains:
            - 'echo'
            - 'copy'
            - 'type'
            - 'file createnew'
            - 'cacls'
    selection_2:
        CommandLine|contains: 'C:\Windows\Fonts\'
    selection_3:
        CommandLine|contains:
            - '.sh'
            - '.exe'
            - '.dll'
            - '.bin'
            - '.bat'
            - '.cmd'
            - '.js'
            - '.msh'
            - '.reg'
            - '.scr'
            - '.ps'
            - '.vb'
            - '.jar'
            - '.pl'
            - '.inf'
            - '.cpl'
            - '.hta'
            - '.msi'
            - '.vbs'
    condition: all of selection_*
falsepositives:
    - Unknown
level: medium

Stages and Predicates

Stage 0: `condition`

all of selection_*

Stage 1: `selection_1`

selection_1:
    CommandLine|contains:
        - 'echo'
        - 'copy'
        - 'type'
        - 'file createnew'
        - 'cacls'

Stage 2: `selection_2`

selection_2:
    CommandLine|contains: 'C:\Windows\Fonts\'

Stage 3: `selection_3`

selection_3:
    CommandLine|contains:
        - '.sh'
        - '.exe'
        - '.dll'
        - '.bin'
        - '.bat'
        - '.cmd'
        - '.js'
        - '.msh'
        - '.reg'
        - '.scr'
        - '.ps'
        - '.vb'
        - '.jar'
        - '.pl'
        - '.inf'
        - '.cpl'
        - '.hta'
        - '.msi'
        - '.vbs'

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	`.bat` corpus 11 (sigma 9, elastic 1, kusto 1) `.bin` `.cmd` corpus 6 (sigma 5, elastic 1) `.cpl` corpus 3 (sigma 3) `.dll` corpus 16 (sigma 16) `.exe` corpus 5 (sigma 5) `.hta` corpus 6 (sigma 6) `.inf` corpus 3 (sigma 3) `.jar` corpus 2 (sigma 2) `.js` corpus 9 (sigma 9) `.msh` `.msi` `.pl` corpus 2 (sigma 2) `.ps` corpus 3 (sigma 3) `.reg` corpus 4 (sigma 3, splunk 1) `.scr` corpus 5 (sigma 5) `.sh` corpus 2 (sigma 2) `.vb` corpus 3 (sigma 3) `.vbs` corpus 7 (sigma 7) `C:\Windows\Fonts\` `cacls` `copy` corpus 5 (sigma 4, chronicle 1) `echo` corpus 8 (sigma 4, splunk 4) `file createnew` corpus 2 (sigma 2) `type` corpus 3 (sigma 2, splunk 1)

`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)

Writing Of Malicious Files To The Fonts Folder

MITRE ATT&CK coverage

Event coverage

Rule body yaml

Stages and Predicates

Stage 0: `condition`

Stage 1: `selection_1`

Stage 2: `selection_2`

Stage 3: `selection_3`

Indicators

Keyboard shortcuts

Search operators

Writing Of Malicious Files To The Fonts Folder

MITRE ATT&CK coverage

Event coverage

Rule body yaml

Stages and Predicates

Stage 0: condition

Stage 1: selection_1

Stage 2: selection_2

Stage 3: selection_3

Indicators

Stage 0: `condition`

Stage 1: `selection_1`

Stage 2: `selection_2`

Stage 3: `selection_3`