How to Conduct Effective Vendor Security Reviews

Vendor security reviews typically employ three complementary assessment methods, applied individually or in combination based on the vendor's risk tier. Questionnaire-based assessments are the most common starting point, using structured sets of questions to gather information about the vendor's security controls, policies, and practices. Documentation reviews involve analysing the vendor's security policies, procedures, certifications, audit reports, and other written evidence to verify the existence and adequacy of their security programme. Technical assessments go deeper, evaluating the vendor's actual security implementation through methods such as vulnerability scanning, penetration testing, configuration review, or architecture analysis.

For most organisations, the questionnaire forms the backbone of the vendor security review programme. It provides a standardised, comparable, and scalable method for evaluating vendors across a consistent set of security domains. However, questionnaires are self-reported and inherently subject to inaccuracy, overstatement, or misinterpretation. They should never be relied upon as the sole assessment method for high-risk or critical vendors. Documentation review provides a second layer of verification — if a vendor claims to have an incident response plan, request the document and evaluate its adequacy. If a vendor claims ISO 27001 certification, request the current certificate and the most recent surveillance audit report.

Technical assessments provide the highest level of assurance but are also the most resource-intensive and often require contractual rights of access. For critical ICT providers, DORA Article 30(3)(e) grants financial entities the right of access, inspection, and audit, which can be exercised directly or through pooled audits and third-party auditors. Technical assessments may include reviewing the vendor's vulnerability scan results, commissioning an independent penetration test of the vendor's environment, evaluating the security architecture of the specific service you consume, or conducting a configuration baseline review of systems that process your data.

Collecting vendor responses is only the first step; the value of the review lies in the quality of the evaluation. Develop a structured evaluation methodology that assigns ratings to each security domain based on the vendor's responses, supporting evidence, and the maturity of their controls relative to the risk tier of the engagement. A common approach uses a four-level rating scale: strong (controls are well-implemented, evidenced, and exceed minimum requirements), adequate (controls meet minimum requirements and are supported by evidence), weak (controls exist but are incomplete, immature, or insufficiently evidenced), and absent (no control or evidence exists).

Evidence evaluation requires critical scrutiny. Vendors often submit policies that have never been operationalised, certifications that cover only part of their service estate, or audit reports with material findings that the vendor presents as clean opinions. Examine the scope of ISO 27001 certificates to confirm they cover the specific services you consume, not just the vendor's corporate headquarters. Review SOC 2 Type II reports for exceptions, management responses, and complementary user entity controls that your organisation must implement. Validate that penetration test reports are current (within the past 12 months), conducted by an independent firm, and cover the relevant service scope.

Document your evaluation findings in a structured review report that maps each security domain to a rating, identifies specific gaps or weaknesses, assesses residual risk, and recommends remediation actions or risk mitigation measures. The report should conclude with an overall risk opinion (acceptable, conditionally acceptable with remediation requirements, or unacceptable) and a clear recommendation to the business on whether to proceed with, continue, or terminate the vendor relationship. Where the review identifies conditions that must be met, define specific remediation milestones with deadlines and verification methods.

For organisations with more than a handful of vendors, the security review programme must be operationalised as a systematic, repeatable, and resource-efficient process. Ad hoc reviews conducted by different analysts using different methods produce inconsistent results that are difficult to aggregate, trend, or report on. Standardisation, tooling, and clear process ownership are the keys to a scalable review programme.

Establish a review calendar that schedules assessments based on vendor risk tier: annual for critical and high-risk vendors, biennial for medium-risk, and trigger-based (new engagement or material change) for low-risk. Assign review responsibility to named analysts with defined backup arrangements. Create template documents for each review type — terms of reference, questionnaire cover letters, evaluation scorecards, review reports, and remediation tracking sheets — to ensure consistency and reduce preparation time.

Invest in vendor risk management tooling that centralises questionnaire distribution and collection, automates scoring and rating calculations, maintains a historical record of all reviews and findings, integrates with continuous monitoring feeds, and generates portfolio-level risk reports and dashboards. Manual spreadsheet-based processes are viable for organisations with fewer than 20 vendors but become unsustainable beyond that scale. Regardless of tooling, maintain clear metrics for the review programme: percentage of vendors reviewed on schedule, average time to complete reviews, number and severity of open findings, remediation completion rates, and trend data on portfolio risk levels. Report these metrics to the vendor governance forum quarterly.