WebApp Offensive Security Engineer

Horizon3 AI

3d•$196,000 - $242,000•Remote

About The Position

Horizon3.ai is seeking a WebApp Offensive Security Engineer with deep, hands-on web application penetration testing experience to enhance their autonomous testing capabilities. This role involves testing real customer web applications using the NodeZero platform as a starting point, identifying and exploiting edge cases, novel attack chains, and business-logic flaws that automated testing may miss. The engineer will work closely with software engineers to translate these discoveries into product improvements, ensuring durable product coverage for all customers. This is a pentesting-first role focused on offensive expertise to test live customer applications, find gaps, demonstrate them, and partner with engineering to close those gaps. The ideal candidate loves breaking real web apps manually, finds satisfaction in discovering what scanners miss, and wants their skills to scale to thousands of customers through the product.

Requirements

Extensive hands-on experience conducting full-scope web application penetration tests.
Deep, practical knowledge of common and not-so-common web vulnerability classes — SQL injection, XSS (reflected, stored, and DOM-based), SSRF, SSTI/CSTI, IDOR/BOLA, authentication and authorization bypass, path traversal, LFI, and similar — including how to chain them to demonstrate impact.
A talent for finding and exploiting business-logic and edge-case flaws that automated scanners routinely miss.
Strong command of proxy tools like Burp Suite and browser developer tools.
Comfort scripting to reproduce findings and build proof-of-concept exploits (e.g., Python or similar) — you don't need to be a professional software engineer, but you should be able to write and read code well enough to demonstrate an exploit and collaborate effectively with engineers.
Ability to clearly communicate attack steps, impact, and remediation guidance to both engineers and non-technical stakeholders.
Curiosity about emerging AI technologies and comfort using AI-assisted tools in your testing and research workflow.
Strong written and verbal communication, including technical documentation.
Ability to manage multiple priorities, work independently, and mentor teammates of varying experience levels.
Quick to learn and adopt new technologies, frameworks, and target stacks as needed.
History of recognized security research, including documented CVE discoveries and responsible disclosure.
Track record of successful bug bounty contributions.

Nice To Haves

Familiarity with how autonomous, agentic, or AI-driven pentesting tools work — and a sharp instinct for where and why they fail.
Experience writing detection or attack content (e.g., Nuclei templates, sqlmap tamper scripts, custom Burp extensions).
Enough software development background to collaborate fluently with engineers on remediation and product coverage.
Familiarity with relational and graph databases, particularly Postgres and Neo4j.
Experience with AI/LLM tools for building agentic workflows (e.g., LangChain, LangFlow) and integrating contextual data using protocols like Model Context Protocol (MCP).
A portfolio of novel web application research, exploits, or edge-case findings you can walk us through.
Demonstrated examples of using AI to enhance or accelerate your testing and exploit development.
OSCP, OSWE, or comparable offensive security certifications.

Responsibilities

Perform hands-on, full-scope web application penetration tests against real customer applications, alongside benchmark and lab targets, to surface vulnerabilities and attack paths.
Review NodeZero results on live customer engagements to identify coverage gaps, blind spots, and missed opportunities — the edge cases and corner-case attack scenarios that autonomous testing doesn't yet handle.
Manually reproduce and validate those edge cases, building reliable, production-safe proof-of-concept exploits and clear test cases that demonstrate the gap end to end — including against live customer environments without disrupting them.
Partner closely with software engineers to translate your findings into product improvements — defining detection logic, attack content, expected behavior, and remediation so NodeZero handles those cases going forward.
Build and maintain a library of regression and benchmark test cases so newly added coverage doesn't silently regress over time.
Monitor production pentests for missed findings and false positives; create and triage Jira tickets to drive issues to resolution.
Work directly with customers and internal teams to investigate findings, explain attack paths, and address questions about web application coverage and results.
Author technical blog posts and research write-ups showcasing new exploits, edge cases, and attack methodologies.
Mentor teammates and contribute to continuous improvement of team processes, methodology, and testing standards.