Full protection of corporate infrastructure today is difficult to achieve without commercial security tools. However, startups, small organizations, and budget-constrained companies often turn to open source solutions as a compromise. This guide focuses on building a minimal security stack that addresses core information security tasks using freely available tools.
A basic stack must cover several key areas: protection of endpoints to detect malware and workstation compromise, network perimeter defense and traffic control, centralized collection and analysis of security events, and user access management through proper authentication and rights separation. The recommendations are intended as a starting point for small infrastructures rather than a complete substitute for enterprise products.
Antivirus Protection
ClamAV is one of the best-known open source antivirus engines with cross-platform support for Linux, Windows, and macOS. On Windows, the graphical frontend ClamWin is available. It is frequently used to scan mail traffic and file repositories in addition to endpoint protection. Other options include the OpenAntiVirus Project and KicomAV.
Installation on Linux uses the commands: apt-get update followed by apt-get install clamav clamav-daemon. Services clamav-freshclam and clamav-daemon handle signature updates and scanning. On Windows, the standard installer is used, and recursive scans are performed with clamscan --recursive.
Network Perimeter Protection
Popular open source firewalls include pfSense, built on FreeBSD with the PF packet filter, its fork OPNsense, and the proxy server Squid. pfSense supports installation of Snort and Suricata for intrusion detection and prevention, as well as Squid for web traffic filtering. Key features encompass multi-WAN load balancing, VPN servers (IPsec, OpenVPN, L2TP, TINC), DHCP services, HAProxy publishing, captive portal support, and log forwarding to external SIEM systems.
Rules for Snort or Suricata can be loaded from ET Open or official VRT feeds. The system can operate in IDS mode for logging only or IPS mode for active blocking. Logs are forwarded via the Status → System Log → Settings section.
Security Event Collection and Analysis
The ELK Stack (Elasticsearch, Logstash, Kibana) enables custom SIEM construction. Logstash and Ingest Pipelines normalize events, while threshold and EQL rules support correlation of authentication failures or suspicious sequences. Wazuh offers a more integrated platform with built-in vulnerability scanning, file integrity monitoring, EDR-like capabilities, and direct mapping to the MITRE ATT&CK framework for threat hunting and IOC enrichment.
Access Management and Authentication
Keycloak provides single sign-on using OAuth2, OIDC, and SAML standards. It authenticates users, issues JWT tokens, and supports integration with LDAP or Telegram. Configuration involves creating an OpenID Connect client, setting valid redirect URIs, and mapping roles in the target application such as Kibana.
These open source components together form a functional baseline for small environments, but they must be tuned to the specific infrastructure, kept updated, and sourced only from active, reputable projects.
