Information System Security Engineer - Senior Security Clearance

Position: Information System Security Engineer - Senior with Security Clearance
In support of a challenging, critical, and rewarding program that provides integrated voice, video, and data services throughout the Information Technology lifecycle, Amentum is seeking Senior Information System Security Engineer (ISSE) to serve as a subject matter expert in the design, implementation, and optimization of enterprise security toolsets. The successful candidate will lead the engineering efforts for the Trellix (ePO) ecosystem and the ACAS (Nessus) suite, ensuring mission-critical assets remain secure, compliant, and resilient.

This role requires a blend of high-level security architecture, hands-on troubleshooting, and the ability to drive secure-by-design principles across the System Development Life Cycle (SDLC). You must be a critical thinker, have a strong work ethic, and be able to work independently or as a member of a team in a dynamic environment. We value candidates who are detail-oriented while also being able to think and react quickly to emerging and unique problem sets.

To be successful, you must be able to rapidly adapt and learn how to operate the front and back end of new products and processes.

Work Schedule:

* 5 Days (Mon - Fri); 8 hrs/Day; 40 hrs/wkly

Essential Responsibilities:

The duties and responsibilities of the Senior Information Systems Security Engineer include, but are not limited to the following:
* Endpoint Security Engineering (Trellix/ePO)
* Ecosystem Management:
Expertly design, configure, and maintain Trellix components (ePO, Trellix Agent, DLP, HIPS, Policy Auditor, ABM, and VSE) across Windows and Linux environments.
* Policy Development:
Author and deploy endpoint security policies for ENS modules (Threat Prevention, Firewall, Web Control) based on DISA STIGs and organizational needs.
* Threat Mitigation:
Develop custom signatures, rules, and exceptions to address zero-day threats and specific operational requirements.
* Operational Continuity:
Validate custom exceptions to ensure uninterrupted operation of mission-critical processes without compromising compliance.
* Vulnerability Management (ACAS/Nessus)
* Architecture & Strategy:
Design enterprise-wide vulnerability scanning strategies and manage the deployment of Security Centers and Nessus scanners.
* Advanced Troubleshooting:
Serve as the final escalation point for complex scan issues, credentialing problems, and system communication failures.
* Risk Reporting:
Configure automated reporting of compliance data to continuous monitoring systems and risk-scoring repositories.
* Security Integration & Engineering
* Tool Orchestration:
Integrate Trellix and ACAS with tools such as Splunk, XSOAR, and Service Now to automate workflows and enhance incident response.
* RMF Support:
Provide authoritative recommendations and ACAS-generated artifacts to support the Assessment and Authorization (A&A) process and RMF packages for Authority to Operate (ATO).
* Strategic Oversight:
Lead the maintenance and scalability of test, development, and operational environments, collaborating with Network and Dev Sec Ops  teams to enhance resilience.
* Multi-Tier Support:
Deliver Tier 1-3 maintenance and incident response for the full cybersecurity portfolio (ACAS, Trellix, Splunk, XSOAR).
* Compliance Mastery:
Deep understanding of DISA STIGs, NIST 800-53, and the Risk Management Framework (RMF).

Minimum Requirements:

* Must have active Top-Secret clearance with SCI or TS with the ability to acquire SCI
* Knowledge and experience with NESSUS/ACAS and Trellix administration
* Experience in Splunk role while working in a Splunk Clustered Environment
* Must be able to work a 40-hour work week, normally Monday through Friday.
* Ability to work overtime during critical peaks and be available to meet last-minute requests for overtime if needed.
* Ability to travel (5-10%) primarily within 75 miles.
* Familiarity with MS Office applications such as Excel, Word, Outlook, SharePoint, Project, and Visio.
* Exceptional attention to detail; excellent verbal and written communication skills; strong critical thinking, organizational, time-management, and problem-solving skills.
* Ability to work both independently and as part of a team in a dynamic environment.

Clearance Required:

* Must have active Top-Secret clearance with SCI or TS with the ability to acquire SCI

Minimum Education:

* Bachelor's Degree in a related field (Cyber and/or Engineering) Minimum Years of

Experience:

* 8 years of relevant experience Required

Certifications:

* Must possess, or be able to obtain, one of the following 8140 IAT Level II or III baseline certifications before a start date:
* Level II certifications include - CCNA Security, GISCP, GSEC, Security+ CE, SSCP
* Level III certifications include - CASP CE, CCNP Security, CISA, CISSP (or Associate), GCED, GCIH

Preferred Qualifications:

* RHEL Administration:
Proficient understanding of Red Hat Enterprise Linux (RHEL) 8 and 9, including the ability to monitor and maintain cybersecurity tools at the OS level.
* SOAR…