/etc/snort

The /etc/snort directory is a crucial part of a Snort installation, housing the configuration files, rules, and other necessary resources for running Snort effectively. Here's an overview of the important files and directories typically found in /etc/snort:

Overview of /etc/snort

1. snort.conf:

   • Description: The main configuration file for Snort.

   • Purpose: Defines the global settings, paths to rules, preprocessors, output plugins, and other operational parameters for Snort.

   • Location: /etc/snort/snort.conf

   • Example:

     var HOME_NET 192.168.1.0/24
     var EXTERNAL_NET any
     
     include $RULE_PATH/local.rules
     include $RULE_PATH/community.rules
     include $RULE_PATH/snort.rules

2. rules/:

   • Description: Directory containing the rule files used by Snort.

   • Purpose: Houses predefined rule sets and custom rules for detecting various types of network traffic anomalies and threats.

   • Location: /etc/snort/rules/

   • Common Files:

     • local.rules: Custom rules defined by the administrator.

     • snort.rules: Official Snort rules.

     • emerging.rules: Rules from Emerging Threats or other sources.

3. classification.config:

   • Description: Defines how alerts are classified and prioritized.

   • Purpose: Maps alert signatures to human-readable descriptions and assigns priorities to different types of alerts.

   • Location: /etc/snort/classification.config

   • Example:

     config classification: attempted-admin,Attempted Administrator Privilege Gain,1
     config classification: attempted-user,Attempted User Privilege Gain,2

4. reference.config:

   • Description: Maps Snort rule references to external security resources.

   • Purpose: Provides links to external documentation and resources related to specific alerts.

   • Location: /etc/snort/reference.config

   • Example:

     config reference: bugtraq https://www.securityfocus.com/bid/
     config reference: cve https://cve.mitre.org/cgi-bin/cvename.cgi?name=

5. sid-msg.map:

   • Description: Maps Snort rule IDs (SIDs) to alert messages and references.

   • Purpose: Ensures that alerts generated by Snort have meaningful messages and references.

   • Location: /etc/snort/sid-msg.map

   • Example:

     1000001 || ICMP PING NMAP || cve,CAN-1999-0524 || url,www.securityfocus.com/bid/277

6. threshold.conf:

   • Description: Defines thresholding and suppression rules.

   • Purpose: Controls how frequently alerts are generated for specific rules to reduce noise and false positives.

   • Location: /etc/snort/threshold.conf

   • Example:

     threshold gen_id 1, sig_id 1000001, type threshold, track by_src, count 5, seconds 60

7. snort_debian.conf (specific to Debian-based systems):

   • Description: Contains settings for running Snort as a service.

   • Purpose: Defines variables used by the Snort init script, such as the interface to listen on and additional command-line options.

   • Location: /etc/snort/snort_debian.conf

   • Example:

     DEBIAN_SNORT_STARTUP="yes"
     INTERFACE="eth0"

8. preproc_rules/:

   • Description: Directory containing rules for preprocessors.

   • Purpose: Houses rules that are applied by Snort preprocessors to detect protocol-specific anomalies and other pre-processing tasks.

   • Location: /etc/snort/preproc_rules/

Example Directory Structure

/etc/snort/
├── classification.config
├── reference.config
├── sid-msg.map
├── snort.conf
├── snort_debian.conf
├── threshold.conf
├── rules/
│   ├── local.rules
│   ├── snort.rules
│   ├── emerging.rules
│   └── ...
├── preproc_rules/
│   ├── preprocessor.rules
│   └── ...

Best Practices

1. Regular Updates: Regularly update Snort rules and configurations to stay protected against new threats.

2. Custom Rules: Create and maintain custom rules in local.rules to address specific needs or threats unique to your environment.

3. Rule Optimization: Review and optimize rules to reduce false positives and improve detection accuracy.

4. Backup Configurations: Keep backups of your configuration files to quickly recover from misconfigurations or system failures.

5. Secure Access: Ensure that the /etc/snort directory and its contents are securely accessible only to authorized users to prevent tampering.

By understanding and properly configuring the files within /etc/snort, administrators can effectively leverage Snort's capabilities to protect their networks from a wide range of threats.