# NCSC shares pen tester advice for CNI resilience

Published: 2026-07-01 · Severity: routine · Sectors: energy, infrastructure, manufacturing, transportation, government-national
Canonical: https://vorant.io/reports/cb9ca562-2120-5cc0-a5bf-bcba34332f32/ncsc-shares-pen-tester-advice-for-cni-resilience

> NCSC-UK summarises guidance from pen testers on how OT/CNI operators can improve segmentation, logging, and monitoring to make attacks harder.

This NCSC-UK blog post is a guidance piece rather than an incident report, drawing on informal feedback from penetration testers working with operational technology (OT) and critical national infrastructure (CNI) organisations. The core recommendation is 'secure by design': building security requirements into systems from the outset rather than retrofitting them, with network segmentation cited as the clearest example. Pen testers emphasised that clear separation between OT control systems and IT business infrastructure, careful management of what crosses that boundary, minimised and standardised OT connectivity, and use of privileged access workstations (PAWs) all make lateral movement significantly harder for attackers (and testers alike).

The article also stresses that strong logging and monitoring—paired with proper alert investigation and exercised incident response plans—compound the benefit of good segmentation, since testers can be detected as they attempt to move through different network zones. A purple team approach (combining red and blue teaming) is recommended to ensure findings are understood and remediated rather than just logged. NCSC also advises using CHECK-scheme assured providers for pen testing, and stresses that testers engaging with OT environments must have relevant OT experience to avoid missing vulnerabilities or causing unintended real-world safety/availability impacts.

There is no specific vulnerability, malware, threat actor, or active exploitation described in this piece; it is best characterised as low-severity, informational best-practice guidance aimed at CNI/OT defenders and pen test commissioners.

Source reporting: https://www.ncsc.gov.uk/blogs/building-more-resilient-cni-what-industry-pen-testers-told-us

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