Potential Attachment Manager Settings Associations Tamper

Status: test
Severity: high
Author: Nasreddine Bencherchali (Nextron Systems)
Source: github.com/SigmaHQ/sigma

Detects tampering with attachment manager settings policies associations to lower the default file type risks (See reference for more information)

Event coverage

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

Rule body yaml

title: Potential Attachment Manager Settings Associations Tamper
id: a9b6c011-ab69-4ddb-bc0a-c4f21c80ec47
status: test
description: Detects tampering with attachment manager settings policies associations to lower the default file type risks (See reference for more information)
references:
    - https://support.microsoft.com/en-us/topic/information-about-the-attachment-manager-in-microsoft-windows-c48a4dcd-8de5-2af5-ee9b-cd795ae42738
    - https://www.virustotal.com/gui/file/2bcd5702a7565952c44075ac6fb946c7780526640d1264f692c7664c02c68465
author: Nasreddine Bencherchali (Nextron Systems)
date: 2022-08-01
modified: 2023-08-17
tags:
    - attack.defense-impairment
logsource:
    category: registry_set
    product: windows
detection:
    selection_main:
        TargetObject|contains: '\SOFTWARE\Microsoft\Windows\CurrentVersion\Policies\Associations\'
    selection_value_default_file_type_rsik:
        TargetObject|endswith: '\DefaultFileTypeRisk'
        Details: 'DWORD (0x00006152)'
    selection_value_low_risk_filetypes:
        TargetObject|endswith: '\LowRiskFileTypes'
        Details|contains: # Add more as you see fit
            - '.zip;'
            - '.rar;'
            - '.exe;'
            - '.bat;'
            - '.com;'
            - '.cmd;'
            - '.reg;'
            - '.msi;'
            - '.htm;'
            - '.html;'
    condition: selection_main and 1 of selection_value_*
falsepositives:
    - Unlikely
level: high

Stages and Predicates

Stage 0: `condition`

selection_main and 1 of selection_value_*

Stage 1: `selection_main`

selection_main:
    TargetObject|contains: '\SOFTWARE\Microsoft\Windows\CurrentVersion\Policies\Associations\'

Stage 2: `selection_value_default_file_type_rsik`

selection_value_default_file_type_rsik:
    TargetObject|endswith: '\DefaultFileTypeRisk'
    Details: 'DWORD (0x00006152)'

Stage 3: `selection_value_low_risk_filetypes`

selection_value_low_risk_filetypes:
    TargetObject|endswith: '\LowRiskFileTypes'
    Details|contains: # Add more as you see fit
        - '.zip;'
        - '.rar;'
        - '.exe;'
        - '.bat;'
        - '.com;'
        - '.cmd;'
        - '.reg;'
        - '.msi;'
        - '.htm;'
        - '.html;'

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	`DWORD (0x00006152)`
`Details`	match	`.bat;` `.cmd;` `.com;` `.exe;` `.htm;` `.html;` `.msi;` `.rar;` `.reg;` `.zip;`
`TargetObject`	ends_with	`\DefaultFileTypeRisk` `\LowRiskFileTypes`
`TargetObject`	match	`\SOFTWARE\Microsoft\Windows\CurrentVersion\Policies\Associations\`

`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:`)
`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 Attachment Manager Settings Associations Tamper

Event coverage

Rule body yaml

Stages and Predicates

Stage 0: `condition`

Stage 1: `selection_main`

Stage 2: `selection_value_default_file_type_rsik`

Stage 3: `selection_value_low_risk_filetypes`

Indicators

Keyboard shortcuts

Search operators

Potential Attachment Manager Settings Associations Tamper

Event coverage

Rule body yaml

Stages and Predicates

Stage 0: condition

Stage 1: selection_main

Stage 2: selection_value_default_file_type_rsik

Stage 3: selection_value_low_risk_filetypes

Indicators

Stage 0: `condition`

Stage 1: `selection_main`

Stage 2: `selection_value_default_file_type_rsik`

Stage 3: `selection_value_low_risk_filetypes`