Suspicious File Creation In Uncommon AppData Folder

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

Detects the creation of suspicious files and folders inside the user's AppData folder but not inside any of the common and well known directories (Local, Romaing, LocalLow). This method could be used as a method to bypass detection who exclude the AppData folder in fear of FPs

MITRE ATT&CK coverage

Tactic	Techniques
Execution	No specific technique
Stealth	No specific technique

Event coverage

Provider	Event	Title
Sysmon	Event ID 11	FileCreate

Rule body yaml

title: Suspicious File Creation In Uncommon AppData Folder
id: d7b50671-d1ad-4871-aa60-5aa5b331fe04
status: test
description: Detects the creation of suspicious files and folders inside the user's AppData folder but not inside any of the common and well known directories (Local, Romaing, LocalLow). This method could be used as a method to bypass detection who exclude the AppData folder in fear of FPs
references:
    - Internal Research
author: Nasreddine Bencherchali (Nextron Systems)
date: 2022-08-05
modified: 2023-02-23
tags:
    - attack.execution
    - attack.stealth
logsource:
    product: windows
    category: file_event
detection:
    selection:
        TargetFilename|startswith: 'C:\Users\'
        TargetFilename|contains: '\AppData\'
        TargetFilename|endswith:
            # Add more as needed
            - '.bat'
            - '.cmd'
            - '.cpl'
            - '.dll'
            - '.exe'
            - '.hta'
            - '.iso'
            - '.lnk'
            - '.msi'
            - '.ps1'
            - '.psm1'
            - '.scr'
            - '.vbe'
            - '.vbs'
    filter_main:
        TargetFilename|startswith: 'C:\Users\'
        TargetFilename|contains:
            - '\AppData\Local\'
            - '\AppData\LocalLow\'
            - '\AppData\Roaming\'
    condition: selection and not filter_main
falsepositives:
    - Unlikely
level: high

Stages and Predicates

Stage 0: `condition`

selection and not filter_main

Stage 1: `selection`

selection:
    TargetFilename|startswith: 'C:\Users\'
    TargetFilename|contains: '\AppData\'
    TargetFilename|endswith:
        - '.bat'
        - '.cmd'
        - '.cpl'
        - '.dll'
        - '.exe'
        - '.hta'
        - '.iso'
        - '.lnk'
        - '.msi'
        - '.ps1'
        - '.psm1'
        - '.scr'
        - '.vbe'
        - '.vbs'

Stage 2: `not filter_main`

filter_main:
    TargetFilename|startswith: 'C:\Users\'
    TargetFilename|contains:
        - '\AppData\Local\'
        - '\AppData\LocalLow\'
        - '\AppData\Roaming\'

Exclusions

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

Field	Kind	Excluded values
`TargetFilename`	match	`\AppData\LocalLow\`
`TargetFilename`	match	`\AppData\Local\`
`TargetFilename`	match	`\AppData\Roaming\`
`TargetFilename`	starts_with	`C:\Users\`

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
`TargetFilename`	ends_with	`.bat` corpus 17 (sigma 17) `.cmd` corpus 8 (sigma 8) `.cpl` corpus 2 (sigma 2) `.dll` corpus 23 (sigma 23) `.exe` corpus 21 (sigma 20, splunk 1) `.hta` corpus 13 (sigma 13) `.iso` corpus 5 (sigma 5) `.lnk` corpus 6 (sigma 6) `.msi` corpus 2 (sigma 2) `.ps1` corpus 17 (sigma 17) `.psm1` corpus 4 (sigma 4) `.scr` corpus 8 (sigma 8) `.vbe` corpus 15 (sigma 15) `.vbs` corpus 18 (sigma 18)
`TargetFilename`	match	`\AppData\` corpus 4 (sigma 4)
`TargetFilename`	starts_with	`C:\Users\` corpus 11 (sigma 9, elastic 2)

`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 File Creation In Uncommon AppData Folder

MITRE ATT&CK coverage

Event coverage

Rule body yaml

Stages and Predicates

Stage 0: `condition`

Stage 1: `selection`

Stage 2: `not filter_main`

Exclusions

Indicators

Keyboard shortcuts

Search operators

Suspicious File Creation In Uncommon AppData Folder

MITRE ATT&CK coverage

Event coverage

Rule body yaml

Stages and Predicates

Stage 0: condition

Stage 1: selection

Stage 2: not filter_main

Exclusions

Indicators

Stage 0: `condition`

Stage 1: `selection`

Stage 2: `not filter_main`