Classified Systems Security Engineer (ISSE)

Castelion Corporation; Torrance (CA); On-site; USD 130,000 - 170,000; Full time

Benefits offered by this job

Equity

PTO

Health benefits

Parental leave

Fitness stipend

Onsite meals

Job summary

Castelion Corporation in Torrance, CA seeks an Information System Security Engineer (ISSE) to translate security requirements into tested controls for classified systems and to harden environments. You will configure SIEM, support RMF/ATO activities, and collaborate with ISSMs, ISSOs, and IT engineers to enable secure product development and testing.

The role requires hands-on experience with DISA STIGs, Windows/Linux security, network segmentation, vulnerability management, and thorough

Qualifications

• Experience supporting classified information systems within approved security boundaries.
• Experience securing Windows and Linux systems, with AD and Group Policy knowledge.
• Experience hardening networks with segmentation and access controls.
• Practical experience applying DISA STIGs and verifying remediation.
• Experience configuring or maintaining a SIEM, including log collection and alerting.
• Experience supporting RMF/ATO activities, security-control evidence, and remediation tracking.
• Ability to troubleshoot security configurations and communicate risks clearly to security/IT teams.
• Experience performing privileged administration on secure/classified systems.

Responsibilities

• Harden Windows, Red Hat Enterprise Linux (RHEL), virtualization platforms, and network infrastructure. Apply DISA STIGs, implement access controls, and test changes with IT engineers to preserve services.
• Configure and maintain SIEM, endpoint protection, and centralized logging; integrate log sources and verify data health.
• Assess vulnerabilities, prioritize findings with system owners, implement fixes, and verify results; document remaining risks.
• Work with ISSM/ISSO on RMF activities to obtain/maintain an Authorization to Operate (ATO) with evidence.
• Review internally developed software and containers; automate security checks and maintain change records.

Skills

DISA STIGs

Windows security

Linux security

RMF/ATO

SIEM tuning

Vulnerability assessment

Network segmentation

Documentation

Privileged access

Security.cfg troubleshooting

Tools

Splunk

Elastic Security

ePO

Nessus/Tenable

SCAP

STIG Viewer

Trivy

GitHub Enterprise

Job description

Castelion Corporation in Torrance, CA seeks an Information System Security Engineer (ISSE) to translate security requirements into tested controls for classified systems and to harden environments. You will configure SIEM, support RMF/ATO activities, and collaborate with ISSMs, ISSOs, and IT engineers to enable secure product development and testing.

The role requires hands-on experience with DISA STIGs, Windows/Linux security, network segmentation, vulnerability management, and thorough