Suspicious Modification Of Scheduled Tasks

Severity: high
Author: Nasreddine Bencherchali (Nextron Systems)
Source: upstream

Detects when an attacker tries to modify an already existing scheduled tasks to run from a suspicious location Attackers can create a simple looking task in order to avoid detection on creation as it's often the most focused on Instead they modify the task after creation to include their malicious payload

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 ID	Title
Sysmon	1	Process creation
Security-Auditing	4688	A new process has been created.

Stages and Predicates

Stage 1: `all of selection_schtasks`

CommandLine|contains: ' /Change '
CommandLine|contains: ' /TN '
Image|endswith: '\schtasks.exe'

Stage 2: `all of selection_susp_locations`

or:
CommandLine|contains: '%ProgramData%'
CommandLine|contains: '%appdata%'
CommandLine|contains: '%comspec%'
CommandLine|contains: '%localappdata%'
CommandLine|contains: 'C:\Perflogs\'
CommandLine|contains: 'C:\ProgramData\'
CommandLine|contains: '\AppData\Local\Temp'
CommandLine|contains: '\AppData\Roaming\'
CommandLine|contains: '\Desktop\'
CommandLine|contains: '\Downloads\'
CommandLine|contains: '\Temporary Internet'
CommandLine|contains: '\Users\Public\'
CommandLine|contains: '\WINDOWS\Temp\'

Stage 3: `all of selection_susp_images`

or:
CommandLine|contains: 'bash '
CommandLine|contains: bash.exe
CommandLine|contains: bitsadmin
CommandLine|contains: certutil
CommandLine|contains: 'cmd /c '
CommandLine|contains: 'cmd /k '
CommandLine|contains: 'cmd /r '
CommandLine|contains: 'cmd.exe /c '
CommandLine|contains: 'cmd.exe /k '
CommandLine|contains: 'cmd.exe /r '
CommandLine|contains: cscript
CommandLine|contains: forfiles
CommandLine|contains: 'hh '
CommandLine|contains: hh.exe
CommandLine|contains: mshta
CommandLine|contains: powershell
CommandLine|contains: regsvr32
CommandLine|contains: rundll32
CommandLine|contains: scrcons
CommandLine|contains: scriptrunner
CommandLine|contains: 'wmic '
CommandLine|contains: wmic.exe
CommandLine|contains: wscript

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
`CommandLine`	match	`/Change` `/TN` `%ProgramData%` corpus 4 (sigma 4) `%appdata%` corpus 4 (sigma 4) `%comspec%` corpus 3 (sigma 3) `%localappdata%` corpus 2 (sigma 2) `C:\Perflogs\` `C:\ProgramData\` corpus 6 (sigma 6) `\AppData\Local\Temp` corpus 8 (sigma 8) `\AppData\Roaming\` corpus 10 (sigma 10) `\Desktop\` corpus 11 (sigma 11) `\Downloads\` corpus 12 (sigma 12) `\Temporary Internet` corpus 6 (sigma 6) `\Users\Public\` corpus 17 (sigma 17) `\WINDOWS\Temp\` corpus 2 (sigma 2) `bash` `bash.exe` `bitsadmin` corpus 5 (sigma 5) `certutil` corpus 5 (sigma 5) `cmd /c` corpus 5 (sigma 5) `cmd /k` corpus 5 (sigma 5) `cmd /r` corpus 5 (sigma 5) `cmd.exe /c` corpus 6 (sigma 6) `cmd.exe /k` corpus 6 (sigma 6) `cmd.exe /r` corpus 6 (sigma 6) `cscript` corpus 12 (sigma 12) `forfiles` corpus 2 (sigma 2) `hh` `hh.exe` `mshta` corpus 11 (sigma 11) `powershell` corpus 16 (sigma 16) `regsvr32` corpus 11 (sigma 11) `rundll32` corpus 19 (sigma 19) `scrcons` `scriptrunner` `wmic` corpus 2 (sigma 2) `wmic.exe` corpus 2 (sigma 2) `wscript` corpus 12 (sigma 12)
`Image`	ends_with	`\schtasks.exe` corpus 45 (sigma 45)