Encrypting Files with WinRar or 7z
editEncrypting Files with WinRar or 7z
editIdentifies use of WinRar or 7z to create an encrypted files. Adversaries will often compress and encrypt data in preparation for exfiltration.
Rule type: eql
Rule indices:
- logs-endpoint.events.*
- winlogbeat-*
- logs-windows.*
- endgame-*
Severity: medium
Risk score: 47
Runs every: 5m
Searches indices from: now-9m (Date Math format, see also Additional look-back time
)
Maximum alerts per execution: 100
References:
Tags:
- Domain: Endpoint
- OS: Windows
- Use Case: Threat Detection
- Tactic: Collection
- Resources: Investigation Guide
- Data Source: Elastic Endgame
- Data Source: Elastic Defend
Version: 110
Rule authors:
- Elastic
Rule license: Elastic License v2
Investigation guide
editTriage and analysis
Investigating Encrypting Files with WinRar or 7z
Attackers may compress and/or encrypt data collected before exfiltration. Compressing the data can help obfuscate the collected data and minimize the amount of data sent over the network. Encryption can be used to hide information that is being exfiltrated from detection or make exfiltration less apparent upon inspection by a defender.
These steps are usually done in preparation for exfiltration, meaning the attack may be in its final stages.
Possible investigation steps
- Investigate the script execution chain (parent process tree) for unknown processes. Examine their executable files for prevalence, whether they are located in expected locations, and if they are signed with valid digital signatures.
- Retrieve the encrypted file.
- Investigate other alerts associated with the user/host during the past 48 hours.
- Check if the password used in the encryption was included in the command line.
-
Decrypt the
.rar
/.zip
and check if the information is sensitive. -
If the password is not available, and the format is
.zip
or the option used in WinRAR is not the-hp
, list the file names included in the encrypted file. - Investigate if the file was transferred to an attacker-controlled server.
False positive analysis
-
Backup software can use these utilities. Check the
process.parent.executable
andprocess.parent.command_line
fields to determine what triggered the encryption.
Response and remediation
- Initiate the incident response process based on the outcome of the triage.
- Prioritize cases that involve personally identifiable information (PII) or other classified data.
- Isolate the involved hosts to prevent further post-compromise behavior.
- Investigate credential exposure on systems compromised or used by the attacker to ensure all compromised accounts are identified. Reset passwords for these accounts and other potentially compromised credentials, such as email, business systems, and web services.
- Run a full antimalware scan. This may reveal additional artifacts left in the system, persistence mechanisms, and malware components.
- Determine the initial vector abused by the attacker and take action to prevent reinfection through the same vector.
- Using the incident response data, update logging and audit policies to improve the mean time to detect (MTTD) and the mean time to respond (MTTR).
Setup
editSetup
If enabling an EQL rule on a non-elastic-agent index (such as beats) for versions <8.2,
events will not define event.ingested
and default fallback for EQL rules was not added until version 8.2.
Hence for this rule to work effectively, users will need to add a custom ingest pipeline to populate
event.ingested
to @timestamp.
For more details on adding a custom ingest pipeline refer - https://www.elastic.co/guide/en/fleet/current/data-streams-pipeline-tutorial.html
Rule query
editprocess where host.os.type == "windows" and event.type == "start" and ( ( ( process.name:"rar.exe" or ?process.code_signature.subject_name == "win.rar GmbH" or ?process.pe.original_file_name == "Command line RAR" ) and process.args == "a" and process.args : ("-hp*", "-p*", "/hp*", "/p*") ) or ( ?process.pe.original_file_name in ("7z.exe", "7za.exe") and process.args == "a" and process.args : "-p*" ) ) and not process.parent.executable : ( "C:\\Program Files\\*.exe", "C:\\Program Files (x86)\\*.exe", "?:\\ManageEngine\\*\\jre\\bin\\java.exe", "?:\\Nox\\bin\\Nox.exe" )
Framework: MITRE ATT&CKTM
-
Tactic:
- Name: Collection
- ID: TA0009
- Reference URL: https://attack.mitre.org/tactics/TA0009/
-
Technique:
- Name: Archive Collected Data
- ID: T1560
- Reference URL: https://attack.mitre.org/techniques/T1560/
-
Sub-technique:
- Name: Archive via Utility
- ID: T1560.001
- Reference URL: https://attack.mitre.org/techniques/T1560/001/
-
Technique:
- Name: Data from Local System
- ID: T1005
- Reference URL: https://attack.mitre.org/techniques/T1005/