How can a Password Filter DLL be used in a domain environment for backdoor or credential theft?

On a domain controller, an attacker with administrative privileges can deploy a malicious Password Filter DLL to capture plaintext passwords from all domain users when they change passwords, or use it as a backdoor to return a reverse shell (e.g., Meterpreter). Since domain controllers have the password complexity policy enabled by default, only reboot is needed for activation. This technique complements other credential theft methods like [retrieving passwords from Windows Credential Manager](/news/penetration-techniques-information-retrieval-from-windows-credential-manager).