Senior Secure Systems Engineer (TS/SCI)

Cornerstone Defense LLC; United States; On-site; USD 150,000 - 190,000; Full time

Benefits offered by this job

Medical, Dental and Vision Plans

Generous PTO Policy

401(k)

HSA and FSA options

Life and Disability Insurance

Tuition Reimbursement and Training

Perks at Work Discount Program

Referral Program

Leads Generation Program

CollegeAmerica 529

Fitness Reimbursement Program

Travel Assistance

Norton Lifelock Benefit Solutions

Life Planning Financial & Legal 9

Job summary

Cornerstone Defense LLC in Reston, VA is seeking a Senior Information Systems Security Engineer (ISSE) with TS/SCI with polygraph to secure mission-critical systems across hybrid, cloud, and air-gapped environments. You will design, engineer, assess, and sustain security controls across complex system architectures, ensuring compliance, operational readiness, and mission resilience.

The ideal candidate brings deep expertise in RMF, STIG compliance, vulnerability scanning, continuous monitoring,

Qualifications

• 7+ years cybersecurity/ISSE experience designing, implementing, and assessing security controls.
• Strong experience with RMF, NIST 800-53, STIGs, ICD 503, FISMA, FedRAMP.
• SIEM experience, including log configuration, dashboards, and analytics (Splunk preferred).
• Hands-on ACAS/Tenable vulnerability scanning and analysis.
• Cloud security experience (AWS/Azure/GovCloud) in IL5–IL6 environments.

Responsibilities

• Engineer, implement, and manage security solutions (firewalls, IDS/IPS, endpoint protection, encryption).
• Perform security assessments across systems, applications, and networks.
• Implement, validate, and maintain RMF NIST 800-53 controls across on-prem, cloud, and air-gapped systems.
• Conduct STIG checks, hardening, and secure configuration updates for OS, applications, network devices, and cloud resources.
• Run ACAS/Tenable scans, analyze vulnerabilities, and drive remediation with engineering teams.
• Configure log ingestion, parsing, and data flows into SIEM platforms (Splunk), and build dashboards and alerts.
• Monitor network traffic, logs, and events to detect anomalies and security threats.
• Conduct incident investigations and provide technical recommendations for mitigation.
• Maintain and enhance incident response plans and continuous monitoring procedures.
• Engineer, configure, and modify secure system and network baselines.
• Analyze and troubleshoot network protocols, packet flows, and configuration issues.
• Produce RMF artifacts, POA&Ms, scan reports, dashboards, and security documentation.
• Collaborate with DevSecOps, system engineering, IT, and development teams to embed security into the lifecycle.
• Write user stories, define security acceptance criteria, and support regression testing.
• Perform system assessments and security engineering within air-gapped and restricted networks.
• Support ongoing continuous monitoring activities and security control reviews.

Skills

ISSE experience

RMF/NIST 800-53

Splunk SIEM

Vulnerability scanning

Cloud security

Incident response

Air-gapped networks

Tools

Fortify

Acunetix

Prisma Cloud

Job description

Cornerstone Defense LLC in Reston, VA is seeking a Senior Information Systems Security Engineer (ISSE) with TS/SCI with polygraph to secure mission-critical systems across hybrid, cloud, and air-gapped environments. You will design, engineer, assess, and sustain security controls across complex system architectures, ensuring compliance, operational readiness, and mission resilience.

The ideal candidate brings deep expertise in RMF, STIG compliance, vulnerability scanning, continuous monitoring,