Trusted Design
Adversaries may attempt to make an executable or file difficult to discover or analyze by encrypting, encoding, or otherwise obfuscating its contents on the system or in transit. This is common behavior that can be used across different platforms and the network to evade defenses.
Payloads may be compressed, archived, or encrypted in order to avoid detection. These payloads may be used during Initial Access or later to mitigate detection. Sometimes a user's action may be required to open and Deobfuscate/Decode Files or Information for User Execution. The user may also be required to input a password to open a password protected compressed/encrypted file that was provided by the adversary.(Citation: Volexity PowerDuke November 2016) Adversaries may also use compressed or archived scripts, such as JavaScript.
Portions of files can also be encoded to hide the plain-text strings that would otherwise help defenders with discovery.(Citation: Linux/Cdorked.A We Live Security Analysis) Payloads may also be split into separate, seemingly benign files that only reveal malicious functionality when reassembled.(Citation: Carbon Black Obfuscation Sept 2016)
Adversaries may also abuse Command Obfuscation to obscure commands executed from payloads or directly via Command and Scripting Interpreter. Environment variables, aliases, characters, and other platform/language specific semantics can be used to evade signature based detections and application control mechanisms.(Citation: FireEye Obfuscation June 2017)(Citation: FireEye Revoke-Obfuscation July 2017)(Citation: PaloAlto EncodedCommand March 2017)
T1027（Obfuscated Files or Information：難読化されたファイルまたは情報）は、攻撃者が自身のコードやデータを、人間やセキュリティ製品にとって「理解不能」または「判別不能」な形式に変更する技術です。
Obfuscated Files or Informationとは、実行ファイル、スクリプト、設定ファイル、または通信データを加工し、その真の意図を隠す行為を指します。
攻撃者は、開発したマルウェアやスクリプトに対して以下のような処理を施します。
$a を $asdf123 など）に変更したり、制御フローを複雑化させる。powershell -e <Base64文字列>T1027は脆弱性を突くものではなく「検知を逃れるための加工」であるため、特定のCVEと結びつくよりは、マルウェアの特性として記録されます。
${jndi:ldap...} の形式から ${${lower:j}ndi:...} のように難読化して、WAF（Web Application Firewall）を回避する試みが多発しました。