Web app security audit cost for a B2B in London in 2026

The verdict in three sentences

A full security audit (code review, OWASP Top 10 testing and application pentest) for a B2B web app in London runs between 6,000 and 18,000 EUR in 2026 depending on attack surface. Remediation of the findings adds 4,000 to 15,000 EUR, and an annual retest keeps you protected for around 3,000 EUR/year. Against the average cost of a data breach (4.88M EUR globally, often 250,000 to 800,000 EUR for a European SME), a preventive audit is one of the best ROIs in your IT budget.

What an audit actually covers and what it costs

A serious audit is not a simple automated scan. It combines tooling (SAST/DAST) with human expertise: reconnaissance, endpoint mapping, manual tests of authentication, authorization, injection and business logic. Here are the 2026 ranges observed in London.

The deliverable drives the value: a report ranking vulnerabilities by criticality (CVSS), with proof of concept, business impact and actionable fixes, is worth far more than a scanner dump.

The cost of doing nothing: breach vs audit

The math is brutal. A single injection or broken access control flaw (IDOR) on a multi-tenant B2B app can expose every customer's data. Here is the economic comparison.

For an app holding customer data, budgeting 10,000 to 20,000 EUR of audit + remediation before commercial launch is a rational trade-off.

Mini case study

Julian, CTO of a 45-person HR SaaS vendor in London, must open his platform to 12 enterprise accounts demanding security proof before signing. He orders a grey-box pentest (9,500 EUR), which uncovers 3 critical flaws (IDOR, poorly validated JWT, unfiltered upload). Remediation: 7,000 EUR. Retest: 3,000 EUR. Total 19,500 EUR.

Return on investment: the 12 contracts represent 540,000 EUR of ARR. Without the audit report, 8 of them required an unlimited liability clause his insurer refused. The audit unlocks 360,000 EUR of signatures for a cost of 19,500 EUR, a 18x ROI in the first year alone, excluding the avoided breach risk.

FAQ

What is the difference between a scan and a pentest? An automated scan (1,200-2,500 EUR) detects known, noisy flaws. A pentest (6,000-18,000 EUR) adds human intelligence on business logic, authentication and attack chains, where 60% of real breaches happen.

How often should an audit be repeated? A retest after every major release and a full pentest yearly (around 3,000-6,000 EUR/year on renewal). Any auth or API rework justifies an immediate targeted audit.

Do I need an audit to raise funds or sign an enterprise account? Increasingly yes. Procurement teams and CTOs demand a recent pentest report (under 12 months) in security questionnaires. It has become a B2B sales accelerator.

Does GDPR require an audit? GDPR requires appropriate technical measures, not a named audit. But in case of an inspection or breach, a recent audit report is the best proof of diligence and sharply reduces sanction risk.

How much does remediation cost if the audit finds many flaws? Expect 4,000 to 15,000 EUR depending on volume and depth. Config flaws are fixed fast; architectural defects (multi-tenancy, permissions) may need several days of development.

Let's scope your project. Describe your application (stack, number of endpoints, APIs and authentication) and your launch deadline: we'll frame the right audit and remediation scope. Detailed quote within 48 h. WhatsApp +221 77 596 93 33.