--- name: detecting-lateral-movement-with-zeek-c2d7c7854a43 description: 'Detect lateral movement in network traffic using Zeek (formerly Bro) log analysis. Parses conn.log, smb_mapping.log, smb_files.log, dce_rpc.log, kerberos.log, and ntlm.log to identify SMB file transfers, NTLM account spray activity, remote service execution, and anomalous internal connections. ' domain: cybersecurity subdomain: network-security tags: - zeek - lateral-movement - smb - dce-rpc - ntlm-spray - network-forensics version: '1.0' author: mahipal license: Apache-2.0 nist_csf: - PR.IR-01 - DE.CM-01 - ID.AM-03 - PR.DS-02 mitre_attack: - T1046 - T1040 - T1557 - T1071 - T1021 --- # Detecting Lateral Movement with Zeek Analyze Zeek network logs to identify lateral movement techniques including SMB admin share access, DCE/RPC remote service creation, NTLM account spray, Kerberos ticket anomalies, and large internal data transfers indicative of staging or exfiltration between hosts. ## When to Use - Hunting for lateral movement after an initial compromise indicator is found on one endpoint - Investigating suspected NTLM account spray or Pass-the-Ticket attacks across the internal network - Monitoring SMB traffic for unauthorized file transfers to admin shares (C$, ADMIN$, IPC$) - Detecting remote service execution via DCE/RPC (PsExec, schtasks, WMI lateral patterns) - Building alerting rules for internal network anomalies in a Zeek-based NSMP deployment - Performing post-incident timeline reconstruction using Zeek logs as a network-level evidence source **Do not use** as a standalone detection mechanism. Zeek sees network traffic only; combine with endpoint telemetry (Sysmon, EDR) for full visibility. Encrypted SMB3 traffic may limit Zeek's visibility into file-level details. ## Prerequisites - Zeek 6.0+ deployed on a network tap or SPAN port monitoring internal VLAN traffic - Zeek SMB analyzer enabled (loaded by default: `@load base/protocols/smb`) - Zeek DCE/RPC analyzer enabled (`@load base/protocols/dce-rpc`) - Zeek Kerberos analyzer enabled (`@load base/protocols/krb`) - Python 3.8+ (standard library only) - Access to Zeek log directory (default: `/opt/zeek/logs/current/`) - Familiarity with Zeek TSV log format (fields separated by `\t`, header lines prefixed with `#`) ## Workflow ### Step 1: Verify Zeek Log Collection Confirm that Zeek is producing the required log files for lateral movement detection: ```bash # Check that all required analyzers are producing logs ls -la /opt/zeek/logs/current/conn.log ls -la /opt/zeek/logs/current/smb_mapping.log ls -la /opt/zeek/logs/current/smb_files.log ls -la /opt/zeek/logs/current/dce_rpc.log ls -la /opt/zeek/logs/current/kerberos.log ls -la /opt/zeek/logs/current/ntlm.log # Quick field check on conn.log zeek-cut id.orig_h id.resp_h id.resp_p proto service < /opt/zeek/logs/current/conn.log | head -20 ``` ### Step 2: Parse conn.log for Internal Lateral Patterns Identify connections between internal hosts on lateral-movement-associated ports: ```bash # Extract SMB connections (port 445) between internal hosts zeek-cut ts id.orig_h id.orig_p id.resp_h id.resp_p proto service duration orig_bytes resp_bytes \ < /opt/zeek/logs/current/conn.log \ | awk '$5 == 445 && $7 == "smb"' # Extract DCE/RPC connections (port 135) zeek-cut ts id.orig_h id.resp_h id.resp_p service \ < /opt/zeek/logs/current/conn.log \ | awk '$4 == 135' # Extract WinRM connections (port 5985/5986) zeek-cut ts id.orig_h id.resp_h id.resp_p service \ < /opt/zeek/logs/current/conn.log \ | awk '$4 == 5985 || $4 == 5986' ``` ### Step 3: Analyze SMB Admin Share Access Detect access to administrative shares (C$, ADMIN$, IPC$) which is the primary vector for tools like PsExec: ```bash # Check smb_mapping.log for admin share access zeek-cut ts id.orig_h id.resp_h path share_type \ < /opt/zeek/logs/current/smb_mapping.log \ | grep -iE '(C\$|ADMIN\$|IPC\$)' # Check smb_files.log for file writes to admin shares zeek-cut ts id.orig_h id.resp_h action path name size \ < /opt/zeek/logs/current/smb_files.log \ | grep -i 'SMB::FILE_WRITE' ``` Deploy the following Zeek script to generate `notice.log` alerts on admin share access: ```zeek @load base/protocols/smb @load base/frameworks/notice redef enum Notice::Type += { Admin_Share_Access }; event smb1_tree_connect_andx_request(c: connection, hdr: SMB1::Header, path: string, service: string) { if ( /\$/ in path ) NOTICE([$note=Admin_Share_Access, $msg=fmt("Admin share access: %s -> %s (%s)", c$id$orig_h, c$id$resp_h, path), $conn=c]); } ``` ### Step 4: Detect DCE/RPC Remote Service Operations Monitor for remote service creation and scheduled task registration via DCE/RPC: ```bash # Look for service control manager operations (PsExec pattern) zeek-cut ts id.orig_h id.resp_h endpoint operation \ < /opt/zeek/logs/current/dce_rpc.log \ | grep -iE '(svcctl|atsvc|ITaskSchedulerService)' ``` ### Step 5: Detect NTLM Account Spray Analyze ntlm.log for authentication anomalies indicating credential reuse. Zeek's ntlm.log does not expose password hashes, so this detection identifies a single account authenticating to many hosts in a short window — the network signature of credential spraying tools like CrackMapExec: ```bash # Extract NTLM authentications zeek-cut ts id.orig_h id.resp_h username domainname server_nb_computer_name success \ < /opt/zeek/logs/current/ntlm.log # Failed NTLM authentications (brute force or credential testing) zeek-cut ts id.orig_h id.resp_h username success \ < /opt/zeek/logs/current/ntlm.log \ | awk '$5 == "F"' # Sort by timestamp for timeline analysis zeek-cut ts id.orig_h id.resp_h username success \ < /opt/zeek/logs/current/ntlm.log \ | sort -k1,1 ``` Deploy the following Zeek script to generate `notice.log` alerts when a single account touches more hosts than the threshold in a rolling window: ```zeek @load base/protocols/ntlm @load base/frameworks/notice redef enum Notice::Type += { NTLM_Account_Spray }; global ntlm_tracker: table[string] of set[addr] &create_expire=5min; const spray_threshold = 3 &redef; event ntlm_log(rec: NTLM::Info) { if ( ! rec?$username || rec$username == "-" ) return; if ( rec$username !in ntlm_tracker ) ntlm_tracker[rec$username] = set(); add ntlm_tracker[rec$username][rec$id$resp_h]; if ( |ntlm_tracker[rec$username]| >= spray_threshold ) NOTICE([$note=NTLM_Account_Spray, $msg=fmt("NTLM account spray: %s -> %d hosts", rec$username, |ntlm_tracker[rec$username]|), $sub=rec$username, $conn=rec$id]); } ``` ### Step 6: Run the Automated Analysis Agent Use the provided agent.py for comprehensive lateral movement detection: ```bash python3 agent.py /opt/zeek/logs/current/ python3 agent.py /opt/zeek/logs/2026-03-18/ # Analyze a specific date ``` ## Verification - Confirm conn.log captures internal SMB (port 445) and DCE/RPC (port 135) connections with correct field parsing - Verify smb_mapping.log correctly logs admin share paths (C$, ADMIN$, IPC$) - Test with a known PsExec execution in a lab: expect to see SMB FILE_WRITE of the service binary followed by DCE/RPC svcctl CreateService - Validate NTLM log parsing by performing a test authentication and confirming username, domain, and success fields are captured; verify the NTLM Account Spray Zeek script generates a `notice.log` entry when the spray threshold is exceeded - Cross-reference Zeek alerts with Sysmon Event ID 1 (Process Creation) on the target host to confirm end-to-end detection - Verify the agent correctly handles both TSV and JSON Zeek log formats --- Source attribution: costrict-plugins-repo Original project: https://github.com/costrict-plugins-repo/mukul975-anthropic-cybersecurity-skills-cybersecurity-skills/blob/1b344d155f00bae5cf27d8eba9508e8f5050d904/skills/detecting-lateral-movement-with-zeek/SKILL.md License: Apache-2.0 License information: https://www.apache.org/licenses/LICENSE-2.0 Original upstream instructions; downloaded from Mega AI Hub. ## Upstream license notice Apache License Version 2.0, January 2004 http://www.apache.org/licenses/ TERMS AND CONDITIONS FOR USE, REPRODUCTION, AND DISTRIBUTION 1. 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