The IBM AS400 (IBM i) has earned its reputation as one of the most stable and reliable enterprise computing systems. For decades, it has powered financial processing, logistics, and healthcare applications. Yet its age and unique architecture often create a false sense of security. In reality, legacy does not mean invulnerable—and security teams must address the technical risks directly through as400 penetration testing.
Why AS400 environments face modern risks
The AS400 was designed in a different era:
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Networks were largely isolated.
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Remote administration was rare.
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Attackers were fewer and less sophisticated.
Fast-forward to today, and most AS400 systems:
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Are connected to cloud services, APIs, and partner networks.
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Support remote access over VPN, SSH, or even Telnet.
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Integrate with modern applications and web frontends.
This evolution expands the attack surface and introduces vulnerabilities that attackers can exploit if security is not rigorously tested.
Common vulnerabilities in AS400 deployments
Technical assessments often uncover recurring issues, including:
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Default or weak credentials: Critical accounts such as QSECOFR left unchanged or reused.
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Over-privileged user profiles: ALLOBJ or other special authorities granted unnecessarily.
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Unencrypted communications: Telnet and FTP still enabled, exposing credentials in plaintext.
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Poorly configured exit programs: Allowing malicious access to critical commands.
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Outdated components: IBM Navigator for i and third-party applications running without patches.
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Insecure integration: APIs and middleware that bypass native IBM i security controls.
These weaknesses may not be detected by generic vulnerability scanners, but they represent real-world risks when chained together.
Technical scope of a pentest
A full AS400 penetration test involves multiple phases, mirroring adversarial tactics:
1. Reconnaissance and enumeration
Mapping available services (5250 emulation, DRDA, ODBC, remote command). Identifying system values, libraries, and exposed interfaces.
2. Authentication attacks
Testing weak passwords, default profiles, and brute-force resistance. Validating whether MFA or IP restrictions are in place.
3. Privilege escalation
Assessing user class assignments, group profiles, and object authorities. Attempting to escalate from standard user to ALLOBJ authority.
4. Lateral movement
Determining if access to AS400 can enable pivoting into adjacent systems, such as ERP or database servers. Reviewing shared accounts and insecure CL programs.
5. Post-exploitation
Evaluating the potential to exfiltrate data, alter records, or maintain persistence. Reviewing whether activity is logged and detected in QAUDJRN.
6. Detection and response testing
Measuring how quickly SOC tools and monitoring systems pick up malicious activity. Many environments lack integration between AS400 logs and SIEM platforms.
Why traditional tools fall short
Most vulnerability scanners offer limited AS400 support. They may flag outdated firmware or open ports but cannot interpret IBM i’s unique object-level authorities or command structures. Only manual, expert-driven testing can reveal complex exploitation paths, such as chaining misconfigured authorities with insecure integrations.
Best practices for securing AS400 environments
Technical teams should focus on:
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Enforcing strong password policies and disabling default accounts.
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Minimizing ALLOBJ and other special authorities.
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Disabling insecure services (Telnet, FTP) and enforcing encrypted protocols.
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Reviewing and hardening exit programs.
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Ensuring patches are applied consistently, even on legacy components.
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Forwarding QAUDJRN events to centralized monitoring systems.
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Conducting regular penetration testing with specialized expertise.
The role of expert partners
AS400 environments require niche knowledge. Partnering with experienced testers—such as www.superiorpentest.com—ensures that tests are accurate, safe, and aligned with both technical realities and business continuity requirements. Their methodology combines IBM i expertise with modern offensive security techniques, providing actionable results.
Final thought: legacy demands vigilance
Technically robust does not mean invulnerable. Without proper testing, AS400 systems risk becoming hidden weak links in enterprise security. By applying rigorous penetration testing, organizations can uncover misconfigurations, validate defenses, and ensure that their legacy platforms remain resilient in a modern threat environment.