Suspicious Environment Variable Has Been Registered

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

Detects the creation of user-specific or system-wide environment variables via the registry. Which contains suspicious commands and strings

MITRE ATT&CK coverage

Tactic	Techniques
Persistence	No specific technique
Stealth	No specific technique

Event coverage

Provider	Event	Title
Sysmon	Event ID 13	RegistryEvent (Value Set)

Rule body yaml

title: Suspicious Environment Variable Has Been Registered
id: 966315ef-c5e1-4767-ba25-fce9c8de3660
status: test
description: Detects the creation of user-specific or system-wide environment variables via the registry. Which contains suspicious commands and strings
references:
    - https://infosec.exchange/@sbousseaden/109542254124022664
author: Nasreddine Bencherchali (Nextron Systems)
date: 2022-12-20
modified: 2023-08-17
tags:
    - attack.persistence
    - attack.stealth
logsource:
    product: windows
    category: registry_set
detection:
    selection_main:
        TargetObject|contains: '\Environment\'
    selection_details:
        - Details:
              - 'powershell'
              - 'pwsh'
        - Details|contains:
              # Add more suspicious strings in env variables below
              - '\AppData\Local\Temp\'
              - 'C:\Users\Public\'
              # Base64 MZ Header
              - 'TVqQAAMAAAAEAAAA' # MZ..........
              - 'TVpQAAIAAAAEAA8A'
              - 'TVqAAAEAAAAEABAA'
              - 'TVoAAAAAAAAAAAAA'
              - 'TVpTAQEAAAAEAAAA'
              # Base64 Invoke- (UTF-8)
              - 'SW52b2tlL'
              - 'ludm9rZS'
              - 'JbnZva2Ut'
              # Base64 Invoke- (UTF-16LE)
              - 'SQBuAHYAbwBrAGUALQ'
              - 'kAbgB2AG8AawBlAC0A'
              - 'JAG4AdgBvAGsAZQAtA'
        - Details|startswith:  # https://gist.github.com/Neo23x0/6af876ee72b51676c82a2db8d2cd3639
              - 'SUVY'
              - 'SQBFAF'
              - 'SQBuAH'
              - 'cwBhA'
              - 'aWV4'
              - 'aQBlA'
              - 'R2V0'
              - 'dmFy'
              - 'dgBhA'
              - 'dXNpbm'
              - 'H4sIA'
              - 'Y21k'
              - 'cABhAH'
              - 'Qzpc'
              - 'Yzpc'
    condition: all of selection_*
falsepositives:
    - Unknown
level: high

Stages and Predicates

Stage 0: `condition`

all of selection_*

Stage 1: `selection_main`

selection_main:
    TargetObject|contains: '\Environment\'

Stage 2: `selection_details`

selection_details:
    - Details:
          - 'powershell'
          - 'pwsh'
    - Details|contains:
          - '\AppData\Local\Temp\'
          - 'C:\Users\Public\'
          - 'TVqQAAMAAAAEAAAA'
          - 'TVpQAAIAAAAEAA8A'
          - 'TVqAAAEAAAAEABAA'
          - 'TVoAAAAAAAAAAAAA'
          - 'TVpTAQEAAAAEAAAA'
          - 'SW52b2tlL'
          - 'ludm9rZS'
          - 'JbnZva2Ut'
          - 'SQBuAHYAbwBrAGUALQ'
          - 'kAbgB2AG8AawBlAC0A'
          - 'JAG4AdgBvAGsAZQAtA'
    - Details|startswith:
          - 'SUVY'
          - 'SQBFAF'
          - 'SQBuAH'
          - 'cwBhA'
          - 'aWV4'
          - 'aQBlA'
          - 'R2V0'
          - 'dmFy'
          - 'dgBhA'
          - 'dXNpbm'
          - 'H4sIA'
          - 'Y21k'
          - 'cABhAH'
          - 'Qzpc'
          - 'Yzpc'

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
`Details`	eq	`powershell` `pwsh`
`Details`	match	`C:\Users\Public\` `JAG4AdgBvAGsAZQAtA` `JbnZva2Ut` `SQBuAHYAbwBrAGUALQ` `SW52b2tlL` `TVoAAAAAAAAAAAAA` `TVpQAAIAAAAEAA8A` `TVpTAQEAAAAEAAAA` `TVqAAAEAAAAEABAA` `TVqQAAMAAAAEAAAA` `\AppData\Local\Temp\` corpus 8 (sigma 8) `kAbgB2AG8AawBlAC0A` `ludm9rZS`
`Details`	starts_with	`H4sIA` `Qzpc` `R2V0` `SQBFAF` `SQBuAH` `SUVY` `Y21k` `Yzpc` `aQBlA` `aWV4` `cABhAH` `cwBhA` `dXNpbm` `dgBhA` `dmFy`
`TargetObject`	match	`\Environment\`

`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 Environment Variable Has Been Registered

MITRE ATT&CK coverage

Event coverage

Rule body yaml

Stages and Predicates

Stage 0: `condition`

Stage 1: `selection_main`

Stage 2: `selection_details`

Indicators

Keyboard shortcuts

Search operators

Suspicious Environment Variable Has Been Registered

MITRE ATT&CK coverage

Event coverage

Rule body yaml

Stages and Predicates

Stage 0: condition

Stage 1: selection_main

Stage 2: selection_details

Indicators

Stage 0: `condition`

Stage 1: `selection_main`

Stage 2: `selection_details`