An audit evaluates technical controls (configurations, patches, segmentation, logs), organisational controls (policies, procedures, roles, training) and physical controls (data-centre access, document destruction).
What is a security audit
A security audit is a systematic, independent process that evaluates an organisation's technical, organisational and procedural controls against a reference framework (ISO 27001, ENS, NIS2, DORA or an internal baseline). Its goal is to identify gaps between what should exist according to the security policy and what is actually implemented and working. Unlike a pentest, which simulates an attack, an audit reviews the entire posture: from firewall configuration and access management to incident-response procedures and employee training.
Why it matters
Without periodic audits, an organisation operates with a false sense of security. Policies are drafted, approved and filed, but nobody verifies whether they are actually followed. Technical controls are deployed but degrade over time: exceptions that become permanent, firewall rules nobody reviews, orphaned accounts with privileges, patches delayed indefinitely. An audit puts numbers on that gap. For a CISO, it is the tool that converts a subjective perception of security into objective evidence. Furthermore, regulations such as ISO 27001, ENS and NIS2 require recurring audits as a compliance requirement. Without them you are not only exposed — you are non-compliant.
Key points
It can be internal (performed by the organisation's own team or an independent department) or external (by an accredited third party). Each type adds different value: internal audits provide continuity, external audits provide independence and credibility before regulators.
The deliverable is a report with findings classified by severity, supporting evidence, associated risk and prioritised remediation recommendations with realistic timelines.
A well-executed audit does not just detect failures — it establishes the baseline from which to measure continuous improvement of the ISMS.
Example: pre-certification audit for ISO 27001
An industrial company with 500 employees wants to achieve ISO 27001 certification. Before the certification audit, it commissions a gap-analysis audit. The auditing team reviews the 114 Annex A controls and discovers that access management has 340 active accounts belonging to former employees, that no documented incident-response procedure exists, that backups are taken but have never been tested in a real restoration exercise, and that 60 % of servers do not have centralised logging enabled. With those findings the company has a concrete remediation plan with clear priorities. Three months later it passes the certification audit with no major non-conformities.
Common mistakes
- Treating the audit as a bureaucratic formality rather than an improvement opportunity. If the sole objective is to pass the exam, findings are papered over instead of fixed, and real risk is not reduced.
- Auditing only the technical layer while ignoring processes and people. There is little point in verifying that a firewall is correctly configured if nobody reviews the rules each quarter or if employees share passwords by email.
- Failing to follow up on findings. An audit without a remediation plan that assigns owners, deadlines and subsequent verification is a report that gets filed and changes nothing.
Related terms
Frequently asked questions
What is the difference between a security audit and a pentest?
An audit evaluates compliance of controls, policies and procedures against a reference framework. A pentest simulates a real attack to find exploitable vulnerabilities. They are complementary: the audit tells you whether you have the right controls, the pentest tells you whether those controls hold up when someone tries to break them.
How often should a security audit be performed?
It depends on the regulatory framework and the level of risk. ISO 27001 requires annual internal audits and certification audits every three years with annual surveillance visits. ENS and NIS2 have their own cycles. At a minimum, an annual internal audit and an external audit every two years is a reasonable practice for most organisations.
Which reference frameworks are used in a security audit?
The most common in Europe are ISO 27001, ENS (for public sector and its suppliers), NIS2 (for essential and important operators), DORA (for financial entities) and GDPR for data protection. CIS Controls and NIST CSF are also used as complementary technical baselines.
Can an internal audit replace an external audit?
Not under most regulatory frameworks. An internal audit provides continuity and contextual knowledge but lacks the independence required by regulators and certification bodies. The ideal approach is to combine both: frequent internal audits to detect problems early and periodic external audits for independent validation.