Senior ISSE – TS/SCI Security Engineer (Onsite)

Castelion Corporation; Torrance (CA); On-site; USD 120,000 - 170,000; Full time

Benefits offered by this job

Equity (long-term)

4 weeks PTO

10 holidays

Health benefits

Parental leave

Fitness stipend

EV charging

Catered meals

Fully stocked kitchen

Job summary

Castelion Corporation in Torrance, CA is seeking an Information System Security Engineer (ISSE) to translate security requirements into tested controls for classified systems and to harden Windows and Linux environments. You will work with ISSMs, ISSOs, and IT engineers to support RMF authorization and ongoing operation.

The role emphasizes secure software review, RMF artifacts, SIEM and log management, vulnerability remediation, and offline patching for air‑gapped environments.

Qualifications

• Hands-on experience securing classified information systems within approved security boundaries.
• Experience securing Windows and Linux servers/workstations; AD/Group Policy knowledge.
• Experience hardening networks via segmentation and access controls.
• Proficient with DISA STIGs and validating configurations.
• Experience configuring or maintaining a SIEM and log analysis.
• Experience with RMF activities and ATO processes.
• Privilege administration on secure/classified systems.

Responsibilities

• Harden Windows, Linux, and network infrastructure per STIGs and test changes with IT engineers.
• Configure and maintain SIEM, endpoint protection, and centralized logging and investigate events.
• Assess configurations, document findings, and track remediation and risks.
• Support RMF activities and provide evidence for ATO and POA&M.
• Review software and containers for security before deployment in classified systems.

Skills

Windows security

Linux security

Network segmentation

SIEM

Vulnerability assessment

RMF/Authorization

Privileged administration

Education

DoD DCWF-compliant cybersecurity certification

Tools

DISA STIGs

SIEM systems (Splunk/Elastic)

ePO / EPP

Vulnerability scanners (Nessus/SCAP)

Job description

Castelion Corporation in Torrance, CA is seeking an Information System Security Engineer (ISSE) to translate security requirements into tested controls for classified systems and to harden Windows and Linux environments. You will work with ISSMs, ISSOs, and IT engineers to support RMF authorization and ongoing operation.

The role emphasizes secure software review, RMF artifacts, SIEM and log management, vulnerability remediation, and offline patching for air‑gapped environments.