How Service Accounts Became the Silent Foothold in Cyberattacks

Read full article from Silverfort here:  https://www.silverfort.com/blog/service-accounts-from-security-measure-to-silent-foothold/?utm_source=nhimg

Service accounts — the backbone of automation in on-premises environments — were designed as a security measure. But in reality, they’re fast becoming one of the most exploited persistence mechanisms in enterprise networks. Built to automate authentication and streamline service operations, these non-human identities (NHIs) can be turned into silent footholds when their password rotation processes are hijacked or disabled.

Microsoft’s password rotation mechanisms for machine accounts and Managed Service Accounts (MSAs) are meant to reduce exposure by automatically changing credentials. Yet, attackers have learned to exploit these safeguards through Man-in-the-Middle (MITM) attacks, RPC abuse, and time synchronization manipulation, allowing them to maintain stealthy, long-term access.

The Hidden Weakness in Password Rotation

Password rotation in Active Directory relies on synchronization between local systems and the Domain Controller (DC). When attackers compromise a machine account, they can abuse the MS-SAMR RPC protocol — specifically the hSamrUnicodeChangePasswordUser2 function — to change passwords directly in AD.
This severs trust between the host and DC, locking out the legitimate machine but leaving the AD object active and attacker-controlled indefinitely.

Meanwhile, time manipulation presents an equally dangerous vector. By intercepting or altering the Network Time Protocol (NTP) sync, attackers can delay or prevent password changes. Since AD uses timestamps like PwdLastSet to determine rotation schedules, rolling the clock back effectively pauses the entire security process — all while maintaining valid Kerberos tickets and seamless authentication across the domain.

Persistence Through Time and Trust

These techniques enable long-term persistence and lateral movement without triggering alerts. Attackers retain access, bypass expiration policies, and maintain stealth operations under the guise of normal account activity. Because the manipulated time appears legitimate to all synchronized systems, even advanced monitoring tools can miss the intrusion.

Securing the Rotation Process

To defend against this silent threat, organizations must:

• Enforce authenticated time synchronization using NTPv4 or secure time seeding.

• Monitor Event ID 4616 (time changes) and Event ID 4742 (password updates).

• Audit PwdLastSet anomalies to detect rotation delays or mismatches.

• Implement Zero Trust principles for service accounts, limiting privilege scope and lifespan.

By securing time synchronization and auditing rotation events, enterprises can close one of the most overlooked backdoors in Active Directory — where trust itself becomes the target.