Information System Security Engineer

Castelion Corporation • Torrance, CA

2d • Onsite

About The Position

The Information System Security Engineer (ISSE) translates security requirements into tested controls for classified information systems. The role hardens systems and networks, configures security tools, investigates findings, and works with Information System Security Managers (ISSMs), Information System Security Officers (ISSOs), and IT engineers to support system authorization and continued operation. The engineer will help build practical security capabilities for disconnected engineering environments supporting product development and testing.

The position is based in Torrance, California and requires full-time onsite presence. Occasional travel and extended hours, including evenings and weekends, may be required to meet aggressive timelines. The role requires U.S. citizenship, an active TS/SCI clearance, applicable program access, and privileged access to classified systems. Required privileged-user training and system-specific authorizations must be completed before privileged duties are performed.

Requirements

• Hands-on experience supporting classified information systems, including work within approved security boundaries and controlled change processes.
• Experience securing Windows and Linux servers or workstations, including authentication, permissions, auditing, and services; working knowledge of Active Directory and Group Policy.
• Experience hardening networks through segmentation, firewall or access-control rules, secure management interfaces, and restriction of unnecessary ports, protocols, and services.
• Practical experience applying DISA STIGs, assessing configurations through automated and manual checks, documenting findings, and verifying corrective actions.
• Experience configuring or maintaining a SIEM, including log collection, searches, alert tuning, and investigation.
• Experience deploying or administering endpoint protection, including policy configuration, agent health, update management, approved exclusions, and troubleshooting.
• Experience using vulnerability-assessment tools to identify findings, evaluate operational impact, and confirm remediation.
• Experience supporting ISSM/ISSO authorization activities, security-control evidence, assessment preparation, and finding closure under the RMF.
• Ability to troubleshoot security configurations, document work clearly, and explain technical risks and proposed fixes to security and IT teams.
• Experience performing privileged administration on secure or classified systems, including administrative account management, access controls, audit logging, and documented configuration changes.
• Must possess and maintain a current cybersecurity certification accepted for the position’s assigned DoD Cyber Workforce Framework (DCWF) work role and proficiency level, and meet applicable DoD 8140.03 and program qualification requirements.
• U.S. citizenship is required.
• Must possess and maintain an active TS/SCI security clearance and meet applicable program-access requirements.
• Must complete required privileged-user training and system-specific authorizations before performing privileged duties.
• Must be able to work full-time onsite in Torrance, California and travel occasionally.
• Must be able to work extended hours, including evenings and weekends, when required to meet aggressive timelines.
• Must be able to lift and move equipment weighing at least 40 pounds when supporting installation or maintenance, with or without reasonable accommodation.
• Employment is contingent on the candidate’s ability to access applicable export-controlled information without additional export licensing being required.

Nice To Haves

• Experience maintaining air-gapped systems, including approved media transfers, offline patches, security-content updates, and local software repositories.
• Experience with Splunk or Elastic Security, including Linux rsyslog, Windows event forwarding, or similar log collection methods.
• Experience with Trellix endpoint protection, ePolicy Orchestrator (ePO), or DLP; Nessus/Tenable; or SCAP assessment tools and STIG Viewer. Equivalent tool experience is relevant.
• Experience securing VMware vSphere/ESXi or Microsoft Hyper-V, storage and backup services, and Juniper or comparable network infrastructure.
• Experience with PowerShell, Bash, Python, or Ansible to automate configuration checks, evidence collection, or approved remediation.
• Experience with eMASS or comparable authorization-documentation tools, initial system authorization, and applicable NIST security controls, DCSA requirements, or the JSIG.
• Experience reviewing software dependencies, container images, and software bills of materials using tools such as Trivy, Anchore, or equivalent.
• Familiarity with approved on-premises source-control and build/release workflows, such as GitHub Enterprise Server.

Responsibilities

• Harden Windows, Red Hat Enterprise Linux (RHEL), virtualization platforms, and network infrastructure; apply DISA STIGs, implement approved access and network-segmentation controls, and test changes with IT engineers while preserving required services.
• Configure and maintain SIEM, endpoint protection, and centralized logging; integrate log sources, tune alerts, verify agent and data-collection health, and support investigation, containment, and recovery of security events.
• Assess vulnerabilities and security configurations, prioritize findings with system owners, implement approved fixes, verify results, document residual risks, and maintain security tools, patches, and update content through approved offline processes.
• Support ISSM and ISSO RMF activities to obtain and maintain an ATO by providing configuration records, scan results, system diagrams, control-implementation evidence, and remediation updates for assessments and POA&Ms.
• Review internally developed software, third-party packages, and container images with developers before they are introduced into classified systems.
• Support controlled testing and release, automate repeatable security checks, and maintain operating procedures and change records.
• Perform privileged administration on secure or classified systems, including administrative account management, access controls, audit logging, and documented configuration changes.
• Travel occasionally and work extended hours, including evenings and weekends, when required to meet timelines.
• Lift and move equipment weighing at least 40 pounds when supporting equipment installation or maintenance, with or without reasonable accommodation.

Benefits

• Meaningful long-term equity for all full-time employees.
• Four weeks of paid time off.
• Ten company-paid holidays.
• Comprehensive health benefits, including employee-covered medical coverage and dependent coverage.
• Dental and vision plans.
• Paid parental leave.
• $100 monthly fitness stipend.
• Onsite EV charging.
• Catered meals, company-covered food during high-demand periods, and a fully stocked kitchen.

What This Job Offers

• Job Type: Full-time
• Career Level: Mid Level
• Education Level: No Education Listed