Medior Security Pentester

keystone-solutions; Brussel; On-site; EUR 55,000 - 85,000; Full time

Job summary

Keystone Solutions is seeking a Medior Security Pentester to join our consultancy mission at a client site. You will perform penetration testing across web apps, APIs and administration portals, networks, and Windows/AD environments, delivering precise, reproducible reports with remediation guidance.

You will collaborate with a senior on complex missions (cloud, containers, mobile, purple teaming) and define scope and rules of engagement.

Qualifications

• Experience conducting penetration tests on web apps, APIs and administration portals.
• Ability to produce technical, reproducible vulnerability reports with impact and remediation guidance.
• Experience in network and Windows/AD pentesting and report writing.

Responsibilities

• Prepare and conduct penetration tests on web apps, networks, and Windows/Active Directory environments, producing technical reports and contributing to remediation efforts with senior support on complex missions.
• Deliver comprehensive, precise, and reproducible technical reports by vulnerability (affected systems, exploitation conditions, evidence, impact, risk, recommendations).
• Define the scope, objectives, and engagement rules of missions in collaboration with a senior.
• Provide simple proof of concepts and scripts tailored to needs.
• Conduct retests to validate the effectiveness of corrections.

Skills

Penetration testing

Web security testing

API security testing

Windows/AD security

Technical reporting

Education

BSc in CS / Cybersecurity / Telecommunications

Tools

Burp Suite

Nmap

Nessus

Kali Linux

Metasploit

OWASP ZAP

Job description

Mission Overview:

Keystone Solutions is seeking a Medior Security Pentester to join our consultancy mission at a client site. The consultant will have confirmed practical experience in penetration testing and will primarily work in three areas: web applications, APIs, and administration portals; network infrastructures and protocols; and Windows and Active Directory environments.

The consultant will autonomously conduct standard complexity missions and contribute to more complex missions (cloud, containers, mobile, purple teaming) under the coordination of a senior profile. All activities will be performed within an authorized framework, based on a defined scope and formalized engagement rules.

Key Responsibilities:

• Prepare and conduct penetration tests on web applications, networks, and Windows/Active Directory environments, producing technical reports and contributing to remediation efforts with senior support on complex missions.
• Deliver comprehensive, precise, and reproducible technical reports by vulnerability (affected systems, exploitation conditions, evidence, impact, risk, recommendations).
• Contribute to executive summaries for management, reviewed by a senior.
• Define the scope, objectives, and engagement rules of missions in collaboration with a senior.
• Provide simple proof of concepts and scripts tailored to needs.
• Conduct retests to validate the effectiveness of corrections.
• Contribute to internal capitalization: methodologies, checklists, report templates, tooling.

Key Skills:

• Structured penetration testing methodology (black/grey/white box); controlled exploitation and post-exploitation.
• Web application and API testing: OWASP Top 10, modern authentication/authorization (OAuth 2.0/OIDC/SAML/JWT), targeted code review.
• Network and infrastructure testing: protocols (TCP/IP, DNS, HTTP/HTTPS/TLS, SMB/LDAP/Kerberos/RDP), segmentation, filtering.
• Windows/Active Directory testing: domain enumeration, Kerberos/NTLM, GPO/ACL, lateral movement, PowerShell.
• Technical report writing and ability to elevate/collaborate with a senior.

Communication and Collaboration:

• Present results to technical teams and project managers; executive summary reviewed by a senior.
• Ability to seek support and accelerate at the right time; teamwork and knowledge sharing.
• Bilingual preferred (French, Dutch) or sufficient knowledge of the second national language; excellent understanding of technical English.

Experience and Education:

• Minimum 3 years of experience (ideally 3 to 5 years); independently conducts standard missions and contributes to complex missions under senior coordination.
• Higher education degree in computer science, cybersecurity, or telecommunications, or equivalent professional experience.
• Preferred certifications: OSCP/OSCP+, Burp Suite Certified Practitioner (BSCP), CRTP; no certification is required.

Why Join Keystone Solutions:

As a consultant at Keystone Solutions, you will engage in dynamic projects that offer a variety of challenges across different client environments. Our commitment to turbo-charged learning ensures that you will have broad professional development opportunities, and we are dedicated to supporting your career growth within our framework. Being a 'K-Stone' means bringing our core values to every engagement.

Duration:

01/11/2026 - 31/12/2026 2 months (full time)

Skills required:

• Applications web et API : injections, IDOR, XSS, SSRF, désérialisation, gestion de sessions/tokens, - Level: Junior - Most recent: Any time
• Métodologies et réfêrentiels : OWASP WSTG/ASVS/API Security Top 10, PTES, MITRE ATT&CK, CVSS, CWE/C - Level: Junior - Most recent: Any time
• Notions complêmentaires (atout) : cloud (Azure/AWS/GCP), Linux, conteneurs/Kubernetes/CI-CD, applica - Level: Junior - Most recent: Any time
• Outillage : Kali/Parrot, Burp Suite/OWASP ZAP, Nmap/Wireshark/Nessus, Metasploit/Impacket/NetExec, B - Level: Junior - Most recent: Any time
• Réseaux et protocoles : TCP/IP, DNS/DHCP/NTP/SNMP, HTTP/HTTPS/TLS, SMB/LDAP/Kerberos/RDP/WinRM, VPN - Level: Junior - Most recent: Any time
• Windows et Active Directory : objets AD, GPO, ACL, relations dàprobatio, Kerberos/NTLM (Kerberoas - Level: Junior - Most recent: Any time

Language requirements:

Dutch

Level Active knowledge

English

Level Active knowledge

French

Level Active knowledge