5. Scan

This chapter is a quick introduction on how to run a THOR scan and how to personalize scans to better fit your environment and expectations.

Please note, the command line arguments are used to fine tune your scans and yield potentially better results for your use cases.

There is no "one fits all" command line argument, but we designed THOR to cover the broadest area with minimal impact in the default operating mode. Default in this case means no additional command line arguments.

5.1. Quick Start

Follow these steps to complete your first THOR scan

Make sure you've read the Before You Begin guide
Open a command line as administrative user
1. Administrator on Windows
2. root on Linux and macOS
Navigate to the folder in which you've extracted the THOR package and placed the license file(s)
Start THOR on your command line
1. thor64.exe on 64-bit Windows systems
2. thor.exe on 32-bit Windows systems
3. thor-linux-64 on x86-64 Linux systems
4. thor-linux on i386 Linux systems
5. thor-macos on macOS
Wait until the scan has completed (this can take between 20 and 180 minutes)
When the scan is finsihed, check the text log and HTML report in the THOR program directory

5.2. Often Used Parameters

Parameter	Description
--soft	Reduce CPU usage, skip all checks that can consume a lot of memory (even if only for a few seconds)
--quick	Perform a quick scan (skips Eventlog and checks only the most relevant folders); see Scan Modes
-e target-folder	Write all output files to the given folder

5.3. Parameters possibly relevant for your Use Case

Parameter

Description

-c, --cpulimit integer

Instruct THOR to pause all scanning if the systems CPU load is higher than the value specified.

Please see CPU Limit (--cpulimit) for more information.

--allhds

By default THOR scans only the C: partition on Windows machines and other files/folders only

in cases in which some reference points to a different partition (e.g. configured web root of IIS is on D:\inetpub, registered service runs from D:\vendor\service)

--lookback days --globallookback

Only check the elements changed or created during the last X days in all available modules (reduces the scan duration significantly)

5.4. Risky Flags

This list contains flags that should better be avoided unless you know exactly what you're doing.

Parameter	Description
--intense	long runtime, stability issues due to disabled resource control
--c2-in-memory	many false positives on user workstations (especially browser memory)
--alldrives	long runtime, stability issues due to scan on network drives or other remote file systems
--mft	stability issues due to high memory usage
--dump-procs	stability issues, possibly high disk space usage (free disk space checks are implemented but may fail)
--full-registry	longer runtime, low positive impact

5.5. Lesser Known But Useful Flags

This list contains flags that are often used by analysts to tweak the scan in useful ways.

Parameter	Description
--allreasons	Show all reasons that led to a certain score
--printshim	Print all available SHIM cache entries into the log
--utc	Print all timestamps in UTC (helpful when creating timelines)
--string-context num-chars	Number of characters preceeding and following the string match to show in the output

5.6. Help and Debugging

You can use the following parameters help you to understand THOR and the output better.

Parameter	Description
--debug	Get debug information if errors occur
--help	Get a help with the most important scan options
--fullhelp	Get a help with all scan options

5.7. Examples

5.7.2. Logging to Syslog Server

The following command instructs THOR to log to a remote syslog server only.

thor64.exe --nohtml --nocsv --nolog -s syslog.server.net

5.7.3. Scan Run on a Single Directory

thor64.exe --lab -p C:\ProgramData
thor64.exe --lab -p I:\mounted\_image\disk1

Important

This feature requires a forensic lab license type which is meant to be used in forensic labs.

You can imitate a lab scan without a lab license with these command line flags:

thor64.exe -a Filescan --intense --norescontrol --nosoft --cross-platform -p C:\ProgramData

5.7.4. Save the result files to a different directory

thor64.exe -s 10.1.5.14 -e Z:\

5.7.5. Only scan the last 7 days of the Windows Eventlog and log files on disk

thor64.exe --lookback 7

5.7.6. Scan System with Defaults and Make a Surface Scan

By default, the surface scan (DeepDive) applies all YARA rules in "./custom-signatures" folder. In this example, all output files are written to a network share.

thor64.exe --deepdivecustom -e \\server\share\thor_output\

5.7.7. Intense Scan and DeepDive on a Mounted Image

The following are two examples on how to scan a mounted image on Windows and Linux.

5.7.7.1. Mounted as Drive Z

thor64.exe --lab --deepdive -p Z:\

5.7.7.2. Mounted as /mnt

thor64.exe --lab --deepdive -p /mnt

Important

Lab scanning mode requires a forensic lab license type, which is meant to be used in forensic labs.

5.7.8. Scan Multiple Paths

thor64.exe --lab -p C:\\ D:\\webapps E:\\inetpub

Hint

non-existent directories will be automatically skipped

5.7.9. Scan All Hard Drives (Windows Only)

thor64.exe --allhds

5.7.10. Don't Scan Recursively

To instruct THOR to scan a folder non-recursively use the :NOWALK suffix.

thor64.exe -a FileScan -p C:\Windows\System32:NOWALK

5.8. Run a Scan with Specific Modules

With the parameter -a you can run a single module or select a set of modules that you'd like to run. All available modules can be found in the section Scan Module Names.

Run a Rootkit check only:

thor64.exe -a Rootkit

Run the Eventlog and file system scan:

thor64.exe –a Eventlog -a Filescan

5.9. Select or filter Signatures during Initialization

THOR 10.7.8 introduces the Init Selector and Init Filter functionalities, allowing users to fine-tune and customize their scanning process for improved accuracy and efficiency.

You can use these flags to limit the signature set to a certain campaign, threat or threat actor.

The filter values are applied to:

Rule name
Tags
Description

Here are some examples:

thor64.exe --init-selector ProxyShell

You can pass multiple selector keywords separated by comma:

thor64.exe --init-selector RANSOM,Lockbit

Or filter a set of signatures that only cause false positives in your environment:

thor64.exe --init-filter AutoIt

It is important to note that while these features offer flexibility and customization, we recommend utilizing a limited signature set only for specific use cases. This approach is particularly suitable when scanning exclusively for indicators related to a specific campaign. By understanding the proper utilization of Init Selectors and Init Filters, users can optimize their scanning process and effectively identify targeted threats.

The main advantages of a reduced signature set are:

improved scan speed
lower memory usage

5.10. PE-Sieve Integration

THOR integrates PE-Sieve, an open-source tool by @hasherezade to check for malware masquerading as benevolent processes.

PE-Sieve can be activated by using the --processintegrity flag. It runs on Windows as part of the ProcessCheck module and is capable of detecting advanced techniques such as Process Doppelganging.

When investigating infections, you can also raise the sensitivity of the integrated PE-Sieve beyond the default with --full-proc-integrity (at the cost of possible false positives).

THOR reports PE-Sieve results as follows:

Findings	THOR's Reporting Level
Replaced PE File	Warning
Implanted PE File	Warning
Unreachable File	Notice
Patched	Notice
IAT Hooked	Notice
Others	No Output in THOR

See the PE-Sieve documentation for more details on these values.

5.11. Multi-Threading

Starting from version 10.6, THOR supports scanning a system with multiple threads in parallel, allowing for a significant increase in speed in exchange for a higher CPU usage.

To use this feature, use the --threads flag which allows you to specify THOR's number of parallel threads.

When using the --lab (Lab Scanning), --dropzone (sample drop zone) or --thunderstorm (Thunderstorm) command line flags, THOR will default to using as many threads as the system has CPU cores; otherwise, THOR will still default to running with a single thread.

Note

The above listed modes are only available with the "Lab", "Thunderstorm" and "Incident Response" license type.

5.11.1. Enabled Modules

Not all modules support multi-threading. It is currently supported for:

Filescan
RegistryChecks
Eventlog
Thunderstorm (Thunderstorm License needed)
Dropzone (Lab License needed)