detecting-lateral-movement-with-zeek

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.

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Repositorio: AgentFlocks/flocks
Última actividad en el origen: 5 de mayo de 2026 a las 05:45
Idioma detectado de SKILL.md: inglés
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name	detecting-lateral-movement-with-zeek
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"]

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:

# 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 |  -20

# 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'

# 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'

@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]);
}

# 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)'

# 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

@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]);
}

python3 agent.py /opt/zeek/logs/current/
python3 agent.py /opt/zeek/logs/2026-03-18/  # Analyze a specific date