Detect Command Obfuscation in Elastic Security
Adversaries may obfuscate content during command execution to impede detection. Command-line obfuscation makes strings and patterns within commands and scripts more difficult to signature and analyze. Techniques include: Base64 encoding, string splitting ('Wor'+'d.Application'), character reordering with rev, caret insertion (p^o^w^e^r^s^h^e^l^l), environment variable substitution (%COMSPEC%), directory traversal to binary paths, XOR encryption, and ROT13. Tools like Invoke-Obfuscation and Invoke-DOSfuscation automate obfuscation. Adversaries including APT32, APT29, MuddyWater, Kimsuky, QakBot, FIN6, Wizard Spider, Cobalt Group, and many ransomware operators use command obfuscation extensively.
MITRE ATT&CK
- Tactic
- Defense Evasion
- Technique
- T1027 Obfuscated Files or Information
- Sub-technique
- T1027.010 Command Obfuscation
- Canonical reference
- https://attack.mitre.org/techniques/T1027/010/
Elastic Detection Query
process where event.type == "start"
and process.name in~ ("cmd.exe", "powershell.exe", "pwsh.exe", "wscript.exe", "cscript.exe")
and (
process.command_line like~ "*^?^?^*"
or process.command_line like~ "*`?`?`*"
or process.command_line like~ "*[Convert]::FromBase64*"
or process.command_line like~ "*-EncodedCommand*"
or process.command_line like~ "*-enc *"
or process.command_line like~ "*iex(*"
or process.command_line like~ "*Invoke-Expression*"
or process.command_line like~ "*%COMSPEC%*"
or process.command_line like~ "*[char]*"
or process.command_line regex~ "(\^[a-zA-Z0-9]){3,}"
or process.command_line regex~ "'[a-z]{2,4}'\s*\+\s*'[a-z]{2,4}'"
)Detects command-line obfuscation techniques targeting cmd.exe, PowerShell, and script hosts. Matches caret insertion, backtick obfuscation, Base64 encoding, string concatenation splitting, environment variable substitution, and Invoke-Expression variants consistent with T1027.010.
Data Sources
Required Tables
False Positives & Tuning
- Legitimate administrative PowerShell scripts that use -EncodedCommand for long command strings in scheduled tasks or remote management tools like Ansible/SCCM
- Security tooling and EDR agents that internally invoke encoded commands for telemetry or response actions
- Developer toolchains (e.g., build scripts, CI runners) that dynamically construct command strings using string concatenation
Other platforms for T1027.010
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 1PowerShell Caret Obfuscation (Invoke-DOSfuscation Style)
Expected signal: Sysmon Event ID 1: cmd.exe with caret-obfuscated command line. The Sysmon CommandLine field will contain the raw obfuscated command. Security Event ID 4688 (if enabled) with the obfuscated command. PowerShell ScriptBlock Log will contain the deobfuscated 'Write-Host caret-obfuscation-test'.
- Test 2PowerShell String Splitting Obfuscation
Expected signal: Sysmon Event ID 1: powershell.exe with string splitting in command line. PowerShell ScriptBlock Log Event ID 4104: will show both the obfuscated and deobfuscated versions. The ScriptBlock log captures the assembled 'Invoke-Expression' call after string joining.
- Test 3Environment Variable Substring Extraction (cmd.exe Level Obfuscation)
Expected signal: Sysmon Event ID 1: cmd.exe with /V:ON flag (enables delayed variable expansion) and environment variable manipulation syntax. The !a:~0,7! syntax extracts a substring from the variable, demonstrating the character assembly obfuscation technique.
- Test 4Base64 Double-Encoding Obfuscation
Expected signal: Sysmon Event ID 1: first powershell.exe with -Command flag and Base64 operations. Sysmon Event ID 1: second powershell.exe with -EncodedCommand flag. PowerShell ScriptBlock Log Event ID 4104: two entries — the outer decoder and the inner decoded command.
References (6)
- https://attack.mitre.org/techniques/T1027/010/
- https://github.com/danielbohannon/Invoke-Obfuscation
- https://github.com/danielbohannon/Invoke-DOSfuscation
- https://web.archive.org/web/20170923102302/https://www.fireeye.com/blog/threat-research/2017/06/obfuscation-in-the-wild.html
- https://redcanary.com/threat-detection-report/techniques/powershell/
- https://learn.microsoft.com/powershell/module/microsoft.powershell.core/about/about_powershell_exe?view=powershell-5.1
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