Detecting and Investigating Lateral Movement: A Network Traffic Analysis Framework
A Technical Guide to Identifying Malicious Pivots, Abused Administrative Protocols, and Incident Triaging Workflows via Passive Network Detection and Response (NDR)
Strategic Threat Briefing: Lateral movement represents one of the most critical execution phases of an internal breach. Unlike external exploitation vectors, an adversary navigating your internal network rarely introduces custom malicious tooling; instead, they hijack legitimate, built-in administrative services to blend into normal baseline traffic. This framework details how to leverage passive, agentless network-level telemetry—such as GREYCORTEX Mendel—to expose unauthorized pivots, differentiate malicious commands from routine IT administration, and map structural attack chains in real time.
The Illusion of Administrative Normalcy
The core challenge in isolating lateral movement lies in the nature of the protocols involved. Services like SMB, RDP, and PSExec form the operational foundation of daily Windows enterprise infrastructure. Because these channels are ubiquitous, threat actors deliberately weaponize them to map internal subnets, locate high-value active directories, and exfiltrate staging assets without triggering traditional perimeter defense alarms.
To expose these hidden threat layers, security analysts must shift focus from single file-scanning controls to comprehensive network metadata analysis, checking what occurred before a connection was established and tracking where a host pivoted immediately afterward.
Analyzing the Four Primary Protocol Vectors of Lateral Movement
Adversaries favor native operating system tools because they guarantee execution while bypassing traditional software blocklists. Security teams must monitor four common protocol architectures for signs of operational abuse:
1. SMB and Windows Administrative Shares (ADMIN$)
Server Message Block (SMB) handles standard file distribution and printer mapping across Windows networks. However, its built-in administrative shares—specifically ADMIN$, which exposes the remote host’s system root directory—present a major exploitation risk. Gaining access to this share allows an attacker to drop binaries, stage execution scripts, and move tools laterally across the environment.
Network Traffic Detection Indicators
Passive NDR engines monitor the application layer of an SMB session to track three critical variables: the active SMB protocol version, the explicit share paths being called, and associated file write/read metrics. While a routine administrator connection rarely triggers unexpected application binaries, an adversarial pivot frequently pairs share access with immediate tool compilation. For instance, detecting an active ADMIN$ session immediately followed by a file operation involving unapproved execution layers (such as a local python.exe deployment) serves as a high-fidelity indicator of compromise.
Investigation Checklist
- Initiator Verification: Correlate the source IP address against authorized administrative jump hosts and active change management logs.
- Post-Access Triggers: Audit the connection payload to check whether the share access was immediately followed by binary file drops or unauthorized script staging.
2. PSExec Service Spawning
PSExec is a lightweight, command-line remote administration utility from the Microsoft Sysinternals suite. It allows IT teams to execute commands on remote endpoints without initializing a full interactive desktop session. Attackers leverage this exact capability to achieve remote shell execution across target subnets.
Network Traffic Detection Indicators
PSExec leaves a distinct signature in network traffic due to its underlying mechanics. Every execution begins by establishing a connection over SMB port 445 to the target’s IPC$ share, followed immediately by installing and starting a temporary Windows service named PSEXESVC. Because this traffic is transmitted in clear text over the wire, an NDR platform can read the exact command string passed to the remote host, providing direct evidence of adversarial intent.
Investigation Checklist
- Operator Authentication: Flag any instances of
PSEXESVC initialization executing outside standard operational maintenance hours or on endpoints with no historical record of remote administration. - Command String Extraction: Inspect the parsed application metadata to analyze the exact command string executed by the service, prioritizing any obfuscated strings or unmapped binary calls.
3. Remote Desktop Protocol (RDP) Sessions
Remote Desktop Protocol (RDP) provides full graphical interface access to remote target machines. If an adversary harvests valid corporate credentials via phishing or local credential dumping, they can initialize an authenticated RDP session to interact directly with internal file networks, bypassing endpoint malware detection layers.
Network Traffic Detection Indicators
Because RDP session traffic is encrypted natively, security analysts cannot directly inspect in-session keystrokes or file actions from network flows alone. Investigation must therefore pivot to analyzing connection metadata, tracking variables like source-destination IP pairs, session durations, and geographic origin indicators.
Session duration metadata provides deeper insights than most analysts realize. While a brief internal RDP session might appear benign, it must be evaluated alongside the prior activity baseline of the initiating host. If that host demonstrated anomalous system queries or unmapped database access immediately before opening the RDP session, the connection is likely part of a lateral chain. Analysts can leverage peer graphing to trace every internal endpoint the host interacted with immediately after the session ended to define the complete blast radius.
Investigation Checklist
- Pre-Session Host Baseline: Analyze the historical activity of the source device to determine if unusual communication trends or scanning behavior preceded the session.
- Downstream Peer Graphing: Leverage network peer graphing to map out and audit every subsequent internal connection initialized by the target host after the RDP session closed.
4. LLMNR Poisoning (Link-Local Multicast Name Resolution)
Link-Local Multicast Name Resolution (LLMNR) serves as a fallback name resolution protocol when standard DNS queries fail. When a Windows endpoint cannot locate a target hostname via DNS, it broadcasts a multicast packet across the local network segment asking if any peer knows the address, allowing any device on the subnet to respond.
Network Traffic Detection Indicators
An attacker can exploit this behavior by running tools like Responder to listen for these multicast queries on UDP port 5355. The attacking device sends a spoofed unicast response claiming to be the target host, forcing the victim machine to attempt authentication and transmit its NTLM credential hash over the wire. A legitimate LLMNR exchange occurs exclusively between a client and a valid asset holder; detecting a unicast response originating from an unexpected IP address with no prior communication history indicates an active poisoning attempt.
Investigation Checklist
- Responder Validation: Compare the IP address of the unicast responder against the authoritative hostname registry, and flag any nodes attempting to answer queries for unmapped domains.
Unifying Parallel Detection Methodologies
Isolating sophisticated lateral movement requires running multiple, complementary analytics engines simultaneously to eliminate individual visibility blind spots:
| Detection Vector | Core Analytical Focus | Lateral Movement Insight Contribution |
|---|
| Network Behavior Analysis (NBA) | Establishes a dynamic baseline of traffic volumes, connection durations, and peer pairings. | Flags structural anomalies, such as a workstation suddenly initiating unmapped connections to high-value database segments. |
| Intrusion Detection System (IDS) | Applies deterministic signature matching against known threat actor methodologies. | Instantly identifies specific exploit strings and known post-exploitation framework patterns, regardless of baseline trends. |
| Log Correlation & Processing | Aggregates application and event logs from endpoints, directories, and internal services. | Enriches network flow metrics with explicit system details, including Windows Event IDs and active process creations. |
When these detection layers operate in tandem within a unified NDR console, disjointed alerts turn into a clear attack timeline. For example, if an IDS signature flags an anomalous ADMIN$ connection while the behavior analysis engine simultaneously logs an unusual surge in internal peer links from that same device, analysts are no longer looking at random noise—they are tracking an active compromise chain.
From Real-Time Triage to Retrospective Forensics
Lateral movement is a progressive sequence that unfolds across multiple protocols, devices, and subnets over time. Because threat actors use standard administrative tools to blend in, catching them requires deep, continuous network visibility to map out both pre-alert behaviors and downstream activities.
This visibility remains valuable long after an active incident is contained. Maintaining a long-term network metadata repository allows security teams to run retrospective analysis months after an event. This historical record ensures your enterprise can confidently execute deep threat hunting exercises, satisfy regulatory compliance audits, and verify the absolute closure of a breach.
