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MediumSplunk security contentRaven Tait +1

Windows AD User Suspicious UPN Change

The following analytic detects a user account modifying its own userPrincipalName (UPN) to match the sAMAccountName of another account via Windows Security Event 4738. This is the setup step of the ResetNightmare…

Description

The following analytic detects a user account modifying its own userPrincipalName (UPN) to match the sAMAccountName of another account via Windows Security Event 4738. This is the setup step of the ResetNightmare attack (CVE-2026-27912), where an attacker with WriteProperty rights on their own UPN attribute spoofs their identity to a target account. The KDC then resolves a ptype=10 (NT-ENTERPRISE) Kerberos pre-authentication request against the spoofed UPN, issuing a kadmin/changepw TGT that can be used to change the target account's password via kpasswd (port 464). Event 4738 is generated when a user account attribute is changed. This analytic filters to events where the SubjectUserSid equals the TargetSid (self-modification), the new UPN value is not a standard UPN (no @ sign), and the value is not a Windows placeholder. A non-UPN value set on one's own account is anomalous and has no legitimate administrative use case.

Detection logic

Detection requirements

Platform
ESXiLinuxmacOSWindows

The rule states no platform. This is derived from the ATT&CK technique it maps to.

Log source category
windows_event_log_security_4738

Known benign triggers

  • Administrators or identity management tools may legitimately set a UPN that does not contain an @ sign during account provisioning or migration workflows. Investigate the SubjectUserName and context to confirm.

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