Is This Sid Taken? Varonis Hazard Labs Finds Synthetic Sid Shot Assault May 2026

This attack involves threat actors with existing high privileges injecting "synthetic" into an Active Directory Access Control List (ACL) . This allows attackers to pre-assign permissions to a SID that does not yet exist in the environment, creating a silent "backdoor" that activates the moment a new account is created with that matching SID. Key Mechanics of the Attack

Yes, identified a technique known as Synthetic SID Injection . This attack involves threat actors with existing high

For more detailed technical analysis, you can view the original research on the Varonis Blog . For more detailed technical analysis, you can view

An attacker with high privileges (but perhaps needing to maintain long-term, hidden access) adds a non-existent SID to a resource's ACL. Since the injection happens before the user exists,

Standard security tools often monitor for changes to ACLs for existing users. Since the injection happens before the user exists, it can bypass traditional monitoring.

A low-level account created later can suddenly "wake up" with Administrative or Domain Admin rights if those rights were pre-injected into the synthetic SID.