Detect Data Encrypted for Impact in CrowdStrike LogScale
Adversaries may encrypt data on target systems or on large numbers of systems in a network to interrupt availability to system and network resources. They can attempt to render stored data inaccessible by encrypting files or data on local and remote drives and withholding access to a decryption key. This may be done in order to extract monetary compensation from a victim in exchange for decryption or a decryption key (ransomware) or to render data permanently inaccessible in cases where the key is not saved or transmitted. In the case of ransomware, it is typical that common user files like Office documents, PDFs, images, videos, audio, text, and source code files will be encrypted and often renamed or tagged with specific file markers. Adversaries may also encrypt critical system files, disk partitions, MBR, virtual machines hosted on ESXi, or cloud storage objects.
MITRE ATT&CK
- Tactic
- Impact
- Technique
- T1486 Data Encrypted for Impact
- Canonical reference
- https://attack.mitre.org/techniques/T1486/
LogScale Detection Query
#repo = "falcon"
| #event_simpleName in ("ProcessRollup2", "SyntheticProcessRollup2", "FileWritten")
| ShadowDeleteMatch := if(
#event_simpleName in ("ProcessRollup2", "SyntheticProcessRollup2") AND
CommandLine = /(?i)(vssadmin\s+delete\s+shadows|wmic\s+shadowcopy\s+delete|bcdedit\s+\/set.*recoveryenabled\s+no|bcdedit\s+\/set.*bootstatuspolicy.*ignoreallfailures|wbadmin\s+delete\s+catalog|wbadmin\s+delete\s+systemstatebackup)/,
1, 0)
| RansomwareFileMatch := if(
#event_simpleName = "FileWritten" AND
TargetFileName = /\.(encrypted|locked|crypt|enc|ransom|cry|lock64|cuba|avos|avos2|play|blackbyte)$/i,
1, 0)
| where ShadowDeleteMatch = 1 OR RansomwareFileMatch = 1
| groupBy([ComputerName, ImageFileName], function=[
sum(RansomwareFileMatch, as=EncryptedFiles),
sum(ShadowDeleteMatch, as=ShadowDeletes),
collect([CommandLine], limit=10, as=Commands),
min(timestamp, as=FirstSeen),
max(timestamp, as=LastSeen)
], limit=10000)
| where EncryptedFiles > 50 OR ShadowDeletes > 0
| RansomwareConfidence := case {
EncryptedFiles > 500 AND ShadowDeletes > 0, "critical";
EncryptedFiles > 200 OR ShadowDeletes > 0, "high";
EncryptedFiles > 50, "medium";
default, "low"
}
| sort(EncryptedFiles, order=desc)
| select([FirstSeen, LastSeen, ComputerName, ImageFileName, EncryptedFiles, ShadowDeletes, RansomwareConfidence, Commands])CrowdStrike LogScale (Falcon) query detecting T1486 Data Encrypted for Impact by correlating ProcessRollup2/SyntheticProcessRollup2 events containing shadow copy deletion and recovery sabotage commands with FileWritten events using known ransomware extensions. Groups by endpoint hostname and initiating process image, applies configurable thresholds, and produces confidence scoring matching the reference KQL/SPL logic. Requires CrowdStrike Falcon EDR file write monitoring policy to be enabled for FileWritten events to be present.
Data Sources
Required Tables
False Positives & Tuning
- Third-party endpoint management or backup agents running on hosts with high file I/O activity (Veeam agent, Acronis Cyber Backup) that trigger FileWritten events for staging files with temporary extensions and may invoke VSS management commands
- CrowdStrike sensor itself or competing EDR products during agent upgrades or file quarantine operations that rename files with modified extensions and execute recovery-related system utilities
- Automated patch management and software deployment platforms (SCCM, Intune, Tanium) running post-patch scripts that invoke bcdedit for boot configuration and generate bulk file writes with non-standard extensions during staged rollouts
Other platforms for T1486
Testing Methodology
Validate this detection against 4 adversary techniques from Atomic Red Team. Each test below lists the behaviour to exercise and the telemetry you should expect to see. Executable commands and cleanup steps are available with Pro.
- Test 1Volume Shadow Copy Deletion via vssadmin
Expected signal: Sysmon Event ID 1: Process creation for vssadmin.exe with 'delete shadows /all /quiet' command line. Windows Security Event ID 4688 with same details. VSS Event ID 8224 in System log confirming shadow deletion.
- Test 2Recovery Sabotage via bcdedit
Expected signal: Sysmon Event ID 1: Two process creation events for bcdedit.exe with /set commands. Windows Security Event ID 4688 with command line auditing. Registry modification events for BCD store changes.
- Test 3Mass File Encryption Simulation
Expected signal: Sysmon Event ID 11: 100 file creation events for .docx files, followed by 100 file rename events to .docx.encrypted. The burst of file operations in a short time window from a single process is the key telemetry pattern.
- Test 4Ransom Note Drop Simulation
Expected signal: Sysmon Event ID 11: 10 file creation events for README_DECRYPT.txt in different directories. The identical filename across multiple directories is the key pattern.
References (10)
- https://attack.mitre.org/techniques/T1486/
- https://www.us-cert.gov/ncas/alerts/TA16-091A
- https://www.fireeye.com/blog/threat-research/2017/05/wannacry-malware-profile.html
- https://www.us-cert.gov/ncas/alerts/TA17-181A
- https://www.us-cert.gov/ncas/alerts/AA18-337A
- https://github.com/redcanaryco/atomic-red-team/blob/master/atomics/T1486/T1486.md
- https://rhinosecuritylabs.com/aws/s3-ransomware-part-1-attack-vector/
- https://www.halcyon.ai/blog/abusing-aws-native-services-ransomware-encrypting-s3-buckets-with-sse-c
- https://thedfirreport.com/2021/11/29/continuing-the-bazar-cycle/
- https://www.crowdstrike.com/en-us/blog/hypervisor-jackpotting-ecrime-actors-increase-targeting-of-esxi-servers/
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