Third-party vendors help your organization scale by running key systems and providing specialized tools. Although they add valuable capabilities, each new integration, login, and data flow also expands your organization’s attack surface. Vendor due diligence works best when it is repeatable, evidence-based, and proportional to the access the provider will have. These seven practical steps can help you evaluate a vendor’s cyber hygiene before work begins.
1. Review Security Certifications and Compliance
Certifications and compliance frameworks are useful signals because they indicate that an independent assessor has evaluated specific controls. They serve as a starting point, so confirm the scope, time period, and any exceptions. Look for materials that match the service being provided:
- SOC 2 Type II for service organizations.
- ISO/IEC 27001 certification for an information security management system.
- HIPAA Security Rule alignment for vendors handling electronic protected health information.
- PCI DSS alignment for vendors that store, process, or transmit payment card data.
Request the complete audit report package and the current scope statement. Pay attention to carve-outs, narrow system boundaries, and user entity controls, since those define what your team must implement and maintain.
2. Deploy Security Questionnaires
Security questionnaires help you verify how a vendor operates on a day-to-day basis, beyond what a certificate title can convey. Keep the scope aligned with the access the vendor will have. NIST’s draft Cybersecurity Supply Chain Risk Management due diligence guide supports using structured supplier assessments to understand risk factors before entering into an agreement.
Questions are more effective when they align with how the service will connect, store data, and be administered. The CISA Software Acquisition Guide can also help shape practical vendor security questions for software and services. Examples that usually produce useful detail:
- What are your data encryption protocols for data at rest and in transit?
- How frequently do you conduct employee security awareness training?
- Can you describe your process for identifying and patching vulnerabilities?
- How do you segregate our data from that of your other clients?
3. Evaluate Their Incident Response Plan
Ask for the vendor’s incident response plan, or a redacted version, and verify that it is actionable. It should outline roles, procedures for escalation outside business hours, customer notification timelines, containment and recovery steps, and evidence preservation.
A vendor that cannot explain who contacts you, when, and with what information creates an avoidable risk when an incident affects your data or service availability.
4. Scrutinize Data Handling and Protection Policies
Vendor data handling is where third-party risk becomes real operational exposure. A study on vendor management revealed that over 60% of organizations have experienced a cybersecurity incident linked to a provider. The findings connected weak contract controls and inadequate data security with business, legal, and financial consequences.
Another audit-focused review highlighted data breaches as a common third-party risk, often tied to vendors that fall short on security controls. These led to unauthorized access and downstream financial, reputational, and legal harm.
Request the vendor’s written policies and verify how they classify data, control access, and log activity. Confirm how they remove your data at contract end, including backups, replicas, and derived datasets used for troubleshooting.
5. Use Third-Party Security Rating Services
Security ratings and external monitoring can add an independent signal, especially when your team cannot deeply test every vendor. These services typically examine what is observable on the internet, including exposed services, configuration drift, certificate hygiene, and other indicators related to external exposure. OWASP’s Attack Surface Management work highlights the risk of weak visibility into externally exposed assets and the need for ongoing monitoring as environments change.
Use the score as a conversation starter, then ask the vendor what drove any concerning findings, what remediation was completed, and how fixes are validated over time. CISA has also advised continuously discovering and validating internet-facing assets through automated asset management and scanning, which aligns with using external signals to spot new exposure earlier.
6. Conduct Penetration Testing and Audits
For high-impact vendors, technical validation can uncover weaknesses that paper reviews cannot. With written permission and clear rules of engagement, penetration testing can evaluate authentication, network exposure, and application security controls.
The U.S. Department of Justice describes penetration testing as a form of internal and external testing designed to identify vulnerabilities, followed by reporting and recommended mitigations. If customer-led testing is not an option, request a recent independent penetration test report summary, a remediation plan, and an agreed-upon method for verifying fixes.
7. Establish a Continuous Monitoring Strategy
A vendor’s posture changes over time as teams, features, and infrastructure evolve. A one-time review can quickly become outdated. Schedule periodic reviews for critical vendors, require notice of material changes to security programs — including new subprocessors — and continue to monitor external signals to identify new exposures early.
Fortify Your Business Through Vigilant Vendor Assessment
Vendor onboarding is a security control shared among procurement, IT, security, and legal. Certifications, incident response materials, data-handling proof, external ratings, and more can provide an evidence-based view of how the vendor operates. When this assessment becomes standard, your organization reduces third-party exposure while preserving uptime, compliance obligations, and customer trust.
Zac Amos is the Features Editor at ReHack, where he covers phishing, ransomware, and other cybersecurity topics. He has also been featured in publications like VentureBeat, the Global Cybersecurity Alliance, and Cyber Defense Magazine.
The opinions expressed in this post belong to the individual contributors and do not necessarily reflect the views of Information Security Buzz.