Important Scheduled Task Deleted/Disabled

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

Detects when adversaries stop services or processes by deleting or disabling their respective scheduled tasks in order to conduct data destructive activities

MITRE ATT&CK coverage

Tactic	Techniques
Execution	`T1053.005` Scheduled Task/Job: Scheduled Task
Persistence	`T1053.005` Scheduled Task/Job: Scheduled Task
Privilege Escalation	`T1053.005` Scheduled Task/Job: Scheduled Task

Event coverage

Provider	Event	Title
Security-Auditing	Event ID 4699	A scheduled task was deleted.
Security-Auditing	Event ID 4701	A scheduled task was disabled.

Rule body yaml

title: Important Scheduled Task Deleted/Disabled
id: 7595ba94-cf3b-4471-aa03-4f6baa9e5fad
related:
    - id: dbc1f800-0fe0-4bc0-9c66-292c2abe3f78 # ProcCreation schtasks delete
      type: similar
    - id: 9ac94dc8-9042-493c-ba45-3b5e7c86b980 # ProcCreation schtasks disable
      type: similar
    - id: 9e3cb244-bdb8-4632-8c90-6079c8f4f16d # TaskScheduler EventLog
      type: similar
status: test
description: Detects when adversaries stop services or processes by deleting or disabling their respective scheduled tasks in order to conduct data destructive activities
references:
    - https://learn.microsoft.com/en-us/previous-versions/windows/it-pro/windows-10/security/threat-protection/auditing/event-4699
    - https://learn.microsoft.com/en-us/previous-versions/windows/it-pro/windows-10/security/threat-protection/auditing/event-4701
author: Nasreddine Bencherchali (Nextron Systems)
date: 2022-12-05
modified: 2023-03-13
tags:
    - attack.execution
    - attack.privilege-escalation
    - attack.persistence
    - attack.t1053.005
logsource:
    product: windows
    service: security
    definition: 'The Advanced Audit Policy setting Object Access > Audit Other Object Access Events has to be configured to allow this detection. We also recommend extracting the Command field from the embedded XML in the event data.'
detection:
    selection:
        EventID:
            - 4699 # Task Deleted Event
            - 4701 # Task Disabled Event
        TaskName|contains:
            # Add more important tasks
            - '\Windows\SystemRestore\SR'
            - '\Windows\Windows Defender\'
            - '\Windows\BitLocker'
            - '\Windows\WindowsBackup\'
            - '\Windows\WindowsUpdate\'
            - '\Windows\UpdateOrchestrator\Schedule'
            - '\Windows\ExploitGuard'
    filter_main_defender_update:
        EventID: 4699
        SubjectUserName|endswith: '$'  # False positives during upgrades of Defender, where its tasks get removed and added
        TaskName|contains: '\Windows\Windows Defender\'
    condition: selection and not 1 of filter_main_*
falsepositives:
    - Unknown
level: high
regression_tests_path: regression_data/rules/windows/builtin/security/win_security_susp_scheduled_task_delete_or_disable/info.yml
simulation:
    - type: atomic-red-team
      name: Windows - Disable the SR scheduled task
      technique: T1490
      atomic_guid: 1c68c68d-83a4-4981-974e-8993055fa034

Stages and Predicates

Stage 0: `condition`

selection and not 1 of filter_main_*

Stage 1: `selection`

selection:
    EventID:
        - 4699
        - 4701
    TaskName|contains:
        - '\Windows\SystemRestore\SR'
        - '\Windows\Windows Defender\'
        - '\Windows\BitLocker'
        - '\Windows\WindowsBackup\'
        - '\Windows\WindowsUpdate\'
        - '\Windows\UpdateOrchestrator\Schedule'
        - '\Windows\ExploitGuard'

Stage 2: `not filter_main_defender_update`

filter_main_defender_update:
    EventID: 4699
    SubjectUserName|endswith: '$'
    TaskName|contains: '\Windows\Windows Defender\'

Exclusions

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

Field	Kind	Excluded values
`SubjectUserName`	ends_with	`$`
`TaskName`	match	`\Windows\Windows Defender\`

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
`TaskName`	match	`\Windows\BitLocker` corpus 2 (sigma 2) `\Windows\ExploitGuard` corpus 2 (sigma 2) `\Windows\SystemRestore\SR` corpus 2 (sigma 2) `\Windows\UpdateOrchestrator\Schedule` `\Windows\Windows Defender\` corpus 2 (sigma 2) `\Windows\WindowsBackup\` corpus 2 (sigma 2) `\Windows\WindowsUpdate\` corpus 2 (sigma 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)

Important Scheduled Task Deleted/Disabled

MITRE ATT&CK coverage

Event coverage

Rule body yaml

Stages and Predicates

Stage 0: `condition`

Stage 1: `selection`

Stage 2: `not filter_main_defender_update`

Exclusions

Indicators

Keyboard shortcuts

Search operators

Important Scheduled Task Deleted/Disabled

MITRE ATT&CK coverage

Event coverage

Rule body yaml

Stages and Predicates

Stage 0: condition

Stage 1: selection

Stage 2: not filter_main_defender_update

Exclusions

Indicators

Stage 0: `condition`

Stage 1: `selection`

Stage 2: `not filter_main_defender_update`