Potential Attachment Manager Settings Associations Tamper

Status: test
Severity: high
Log source: product windows, category registry_set
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)

MITRE ATT&CK coverage

Tactic	Techniques
Defense Impairment	No specific technique

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:
        - '.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:`)
`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)

Potential Attachment Manager Settings Associations Tamper

MITRE ATT&CK coverage

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

MITRE ATT&CK coverage

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`