What are the signs that pass-the-hash activity is underway in a network?

How to recognise pass-the-hash from normal admin traffic

Pass-the-hash usually stands out because the attacker is authenticating with a stolen NTLM hash rather than a legitimately used interactive credential. That creates a pattern of remote administration that looks valid at the protocol layer but odd in context: the source host, timing, peer relationship, and follow-on actions do not match the account’s normal working pattern. Identity Threat Detection and Response (ITDR) Guide is a useful companion when you need to separate routine lateral administration from identity misuse.

In practice, the strongest clue is not one packet or one login, but a cluster of mismatches. Administrators often use a small set of jump hosts, management tools, and predictable target ranges. Pass-the-hash activity tends to break that consistency by showing privileged access from an unusual workstation, a server that should not be an admin origin, or a host that has no business relationship with the target system. That is why defenders should compare authentication events against established admin paths rather than treat each success as benign.

Which host and protocol patterns matter most

Unexpected SMB and RDP use between systems is a classic signal because those protocols are commonly used for remote execution, remote file operations, and interactive control during lateral movement. When those sessions involve accounts that normally do not log on that way, or when the source is a nonstandard endpoint, the event deserves attention. The same is true when a privileged account suddenly appears on multiple hosts in quick succession, especially if those hosts sit outside the administrator’s usual support set.

Another high-value clue is privileged authentication from unusual hosts. A helpdesk or workstation account that suddenly authenticates as an admin to servers, or a server account that appears to initiate interactive remote access, often indicates stolen credentials being replayed. Correlating those events with edge alerts, endpoint detections, and recent credential-dumping activity helps separate a single odd login from an active intrusion chain. For attack-chain context, the MITRE ATT&CK Enterprise Matrix remains a strong reference for mapping credential access and lateral movement behaviours.

What usually happens next in a compromise

Pass-the-hash rarely appears alone. It is often part of a sequence that starts with credential dumping, then moves through lateral movement, privilege escalation, and finally data theft or ransomware deployment. The practical sign is not only the login itself, but what that login unlocks. If a privileged session is followed by service creation, remote execution, new administrative shares, suspicious remote registry access, or broad host-to-host movement, the activity is far more concerning than an isolated authentication success.

Defenders should also watch for concentration effects, where one compromised account touches many systems in a short window. That pattern suggests an operator is using the same stolen material to test access until they find the most valuable foothold. Once that starts, the response window narrows quickly, so the detection value comes from correlating identity, host, and action data early enough to contain the blast radius before encryption or exfiltration begins.

Risk and Threat Considerations

Pass-the-hash is risky because it converts a stolen secret into reusable network access without needing the original password. In many environments that means an attacker can move laterally while appearing to authenticate successfully, which reduces the value of simple success-failure monitoring and increases the importance of behavioural context.

Failure mechanism: The attacker reuses captured hash material to authenticate over SMB, RDP, or related Windows pathways, then expands access from host to host while blending into ordinary administrative traffic.

Impact: A single compromised account can become a pivot into multiple systems, enabling privilege escalation, ransomware staging, credential harvesting, and faster domain-wide compromise.

Practitioner Guidance

What to prioritise: Treat unusual privileged remote logons as a correlation problem, not a single-event alert. Prioritise source host, target host, logon type, protocol, and whether the account normally administers that system. If the account is privileged and the origin is unexpected, escalate quickly even if the authentication itself succeeded.

What to verify: Confirm whether the account used a known management path, whether the source device is authorised for admin work, and whether the logon was followed by remote execution, share access, or service creation. A clean-looking authentication event can still be malicious if the surrounding behaviour is off-pattern.

Practitioner takeaway: The most useful signal is not “someone logged in”, but “a privileged identity authenticated from an implausible place and then behaved like an intruder.”

Related resources from NHI Mgmt Group

• What are the signs that pass-the-hash or pass-the-ticket activity is occurring inside a Windows environment?
• What breaks when organisations do not monitor for Pass the Hash activity?
• What are the signs that a crypto laundering network is operating at scale rather than as isolated vendor activity?
• What are the signs that corporate espionage activity is already underway in an organisation?