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ATT&CK Technique

Reversible Encryption

T1556.005 · defense-impairment, persistence, credential-access

An adversary may abuse Active Directory authentication encryption properties to gain access to credentials on Windows systems. The AllowReversiblePasswordEncryption property specifies whether reversible password encryption for an account is enabled or disabled. By default this property is disabled (instead storing user credentials as the output of one-way hashing functions) and should not be enabled unless legacy or other software require it.

If the property is enabled and/or a user changes their password after it is enabled, an adversary may be able to obtain the plaintext of passwords created/changed after the property was enabled. To decrypt the passwords, an adversary needs four components: 1. Encrypted password (G$RADIUSCHAP) from the Active Directory user-structure userParameters 2. 16 byte randomly-generated value (G$RADIUSCHAPKEY) also from userParameters 3.

Global LSA secret (G$MSRADIUSCHAPKEY) 4. Static key hardcoded in the Remote Access Subauthentication DLL (RASSFM.DLL) With this information, an adversary may be able to reproduce the encryption key and subsequently decrypt the encrypted password value. An adversary may set this property at various scopes through Local Group Policy Editor, user properties, Fine-Grained Password Policy (FGPP), or via the ActiveDirectory PowerShell module.

For example, an adversary may implement and apply a FGPP to users or groups if the Domain Functional Level is set to "Windows Server 2008" or higher. In PowerShell, an adversary may make associated changes to user settings using commands similar to Set-ADUser -AllowReversiblePasswordEncryption $true.

Windows
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Mitigations

2
MITRE ATT&CK mitigations - vendor-agnostic guidance for reducing exposure to this technique.
M1026Privileged Account Management

Privileged Account Management focuses on implementing policies, controls, and tools to securely manage privileged accounts (e.g., SYSTEM, root, or administrative accounts). This includes restricting access, limiting the scope of permissions, monitoring privileged account usage, and ensuring accountability through logging and auditing.

Account Permissions and Roles
  • Implement RBAC and least privilege principles to allocate permissions securely.
  • Use tools like Active Directory Group Policies to enforce access restrictions.
Credential Security
  • Deploy password vaulting tools like CyberArk, HashiCorp Vault, or KeePass for secure storage and rotation of credentials.
  • Enforce password policies for complexity, uniqueness, and expiration using tools like Microsoft Group Policy Objects (GPO).
Multi-Factor Authentication (MFA)
  • Enforce MFA for all privileged accounts using Duo Security, Okta, or Microsoft Azure AD MFA.
Privileged Access Management (PAM)
  • Use PAM solutions like CyberArk, BeyondTrust, or Thycotic to manage, monitor, and audit privileged access.
Auditing and Monitoring
  • Integrate activity monitoring into your SIEM (e.g., Splunk or QRadar) to detect and alert on anomalous privileged account usage.
Just-In-Time Access
  • Deploy JIT solutions like Azure Privileged Identity Management (PIM) or configure ephemeral roles in AWS and GCP to grant time-limited elevated permissions.
Tools for Implementation Privileged Access Management (PAM)
  • CyberArk, BeyondTrust, Thycotic, HashiCorp Vault.
Credential Management
  • Microsoft LAPS (Local Admin Password Solution), Password Safe, HashiCorp Vault, KeePass.
Multi-Factor Authentication
  • Duo Security, Okta, Microsoft Azure MFA, Google Authenticator.
Linux Privilege Management
  • sudo configuration, SELinux, AppArmor.
Just-In-Time Access
  • Azure Privileged Identity Management (PIM), AWS IAM Roles with session constraints, GCP Identity-Aware Proxy.
M1027Password Policies

Set and enforce secure password policies for accounts to reduce the likelihood of unauthorized access. Strong password policies include enforcing password complexity, requiring regular password changes, and preventing password reuse.

Windows Systems
Use Group Policy Management Console (GPMC) to configure
  • Minimum password length (e.g., 12+ characters).
  • Password complexity requirements.
  • Password history (e.g., disallow last 24 passwords).
  • Account lockout duration and thresholds.
Linux Systems
Configure Pluggable Authentication Modules (PAM)
  • Use pam_pwquality to enforce complexity and length requirements.
  • Implement pam_tally2 or pam_faillock for account lockouts.
  • Use pwunconv to disable password reuse.
Password Managers
  • Enforce usage of enterprise password managers (e.g., Bitwarden, 1Password, LastPass) to generate and store strong passwords.
Password Blacklisting
  • Use tools like Have I Been Pwned password checks or NIST-based blacklist solutions to prevent users from setting compromised passwords.
Regular Auditing
  • Periodically audit password policies and account configurations to ensure compliance using tools like LAPS (Local Admin Password Solution) and vulnerability scanners.
Tools for Implementation Windows
  • Group Policy Management Console (GPMC): Enforce password policies.
  • Microsoft Local Administrator Password Solution (LAPS): Enforce random, unique admin passwords.
Linux/macOS
  • PAM Modules (pam_pwquality, pam_tally2, pam_faillock): Enforce password rules.
  • Lynis: Audit password policies and system configurations.
Cross-Platform
  • Password Managers (Bitwarden, 1Password, KeePass): Manage and enforce strong passwords.
  • Have I Been Pwned API: Prevent the use of breached passwords.
  • NIST SP 800-63B compliant tools: Enforce password guidelines and blacklisting.
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Detection Coverage

0/6 layers
Coverage across standard detection surfaces. Rows marked none have no rule of that type mapped. Some are real blind spots worth closing; others are simply not applicable to this technique (e.g. YARA matches malware files, not network behaviour).
Behavioral / log (Sigma) none
Analytics (MITRE CAR) none
Runtime / container (Falco) none
File / malware (YARA) none
Network (Suricata/Snort) none
Vuln scan (Nuclei) none
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