Functional Functional Always active

The technical storage or access is strictly necessary for the legitimate purpose of enabling the use of a specific service explicitly requested by the subscriber or user, or for the sole purpose of carrying out the transmission of a communication over an electronic communications network.

Preferences Preferences

The technical storage or access is necessary for the legitimate purpose of storing preferences that are not requested by the subscriber or user.

Statistics Statistics

The technical storage or access that is used exclusively for statistical purposes. The technical storage or access that is used exclusively for anonymous statistical purposes. Without a subpoena, voluntary compliance on the part of your Internet Service Provider, or additional records from a third party, information stored or retrieved for this purpose alone cannot usually be used to identify you.

The technical storage or access is required to create user profiles to send advertising, or to track the user on a website or across several websites for similar marketing purposes.

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Cyber Security: What is external penetration testing (external network)?

EJN Labs

September 28, 2025

External penetration testing is a security assessment that targets an organisation’s internet-facing systems from the position of an external attacker with no prior access. The scope typically includes public IP ranges, web applications, VPN endpoints, mail servers, remote management interfaces, and any other service reachable from the public internet.

Scope

Scope is defined by the client up front and usually expressed as IP ranges or domain names. The tester confirms ownership of in-scope assets before testing begins. Out-of-scope assets are documented explicitly to avoid accidental coverage. For organisations with significant cloud presence, scoping also covers public S3 buckets, exposed serverless endpoints, and externally accessible cloud management interfaces.

Methodology

Engagements follow recognised frameworks such as the Penetration Testing Execution Standard (PTES) and CREST or NCSC CHECK methodology. A typical phased approach: open-source intelligence and passive reconnaissance to map the attack surface; active scanning to enumerate hosts, ports, and services; vulnerability identification with both automated and manual technique; exploitation to validate findings; post-exploitation to demonstrate impact and pivot opportunities; and reporting.

Common findings

Exposed management interfaces (SSH, RDP, database admin), missing patches on internet-facing services, weak TLS configurations, default credentials on appliances, information disclosure through verbose error messages or directory listings, subdomain takeover via dangling DNS, and authentication weaknesses such as missing rate limits or absent multi-factor authentication. Findings are rated by severity and business impact, not by raw CVSS alone.

What a good report contains

An executive summary aimed at non-technical stakeholders, a technical write-up with reproduction steps for each finding, evidence (screenshots, request and response captures, command output), remediation guidance, and a prioritised action list. Many CREST member firms also include a retest as part of the engagement so that fixes can be verified.

When to commission an external test

Annually as a baseline; after major changes to the public estate (new application launch, migration to a new cloud, acquisition); to meet contractual or regulatory requirements (PCI DSS, ISO 27001, NHS DSPT, FCA expectations).

EJN Labs

We are an CREST certified, AI led threat research and cyber security services company based in Canary Wharf, London, UK. Schedule a call to find out more!