NIS2 guide · 7 min
Your external security posture under NIS2: what suppliers and customers can see
Under NIS2, your customers are accountable for the security of their suppliers (Article 21(2)(d)), and they increasingly assess that risk from the outside, using only what is publicly visible: your email authentication, your certificates, and what of your infrastructure is exposed to the internet. These are the same signals an attacker sees first. This guide explains the external signals that shape how you are judged as a supplier, why each matters, and how to check and fix them.
Key takeaways
- • NIS2 pushes supplier assessment down the chain; much of it starts with your publicly visible posture.
- • The strongest signals are email spoofability (SPF/DMARC), certificate hygiene and internet-exposed systems.
- • You can see and fix most of these yourself in minutes, before a customer or an attacker does.
Why the outside view matters under NIS2
NIS2 Article 21(2)(d) makes an in-scope company responsible for the cyber risk carried by its direct suppliers. Because a buyer cannot audit every supplier in depth, the practical first pass is the external view: signals visible without any access to your systems. A weak external signal does not prove you are insecure, but it is what a customer notices, what a questionnaire is checked against, and what an attacker probes first. Getting it right is low-cost and high-signal.
Official source: NIS2 Directive on EUR-Lex — Article 21(2) (security measures) and 21(2)(d) (supply-chain security).
The external signals that shape how you are judged
None of these require access to your systems; all are visible from the public internet. They map to the measures NIS2 expects and to how attackers actually operate.
Email spoofability (SPF and DMARC)
If your domain publishes no SPF or DMARC record, or DMARC is set to p=none, anyone can send email that appears to come from you. This is the mechanism behind phishing and CEO-fraud (BEC), and it is trivially checkable in your public DNS.
TLS certificate hygiene
Expired or soon-to-expire certificates on your main services signal weak operational control and can break trust and availability. Certificate transparency logs also make your certificate history public.
Internet-exposed non-production and admin systems
Development, staging or admin hostnames reachable from the internet widen your attack surface and often lack production-grade hardening. They frequently surface in public certificate transparency logs.
Leaked credentials and breach exposure
Employee credentials exposed in public breach and infostealer datasets are a direct route in. This is external, public information an attacker can act on before you notice.
Web transport hardening (HSTS and headers)
Missing HSTS and related headers are minor individually, but together they indicate how consistently the basics are applied. Assessors read them as a proxy for operational maturity.
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How to check it, and keep it right
You can check most of these yourself in minutes, with public tools and your own DNS. The harder part is keeping them right over time: a certificate expires, a new subdomain is exposed, credentials leak. Continuous external monitoring watches these signals for your own domain and for your suppliers, and maps each finding to the relevant NIS2 article, so you see and fix issues before a customer's assessment or an attacker does.
Common mistakes
- ✕Treating email authentication as done once SPF exists, while DMARC stays at p=none and blocks nothing.
- ✕Fixing the main website but leaving dev, staging or admin hosts exposed and unhardened.
- ✕Assuming 'we passed the questionnaire' means the external reality still matches months later.
- ✕Never checking what public breach data already exposes about your accounts.
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Last reviewed: 19 June 2026
This guide is general information about EU law, not legal advice. NIS2 takes effect through each EU Member State's national transposition law, which can differ in detail. Verify the obligations that apply to you with your competent authority or legal counsel.