How Organizations Achieve Zero Trust for Third-Party and Contractor Access

Zero trust is a security model that assumes no user, device, or network path is inherently safe, even if it appears to be “inside” the perimeter. For third-party users and contractors, the mantra “never trust, always verify” acknowledges a hard truth: you don’t control their endpoints, identity hygiene, or staffing changes.

Rather than granting broad network reach, the approach delivers tightly scoped, identity-aware access to specific applications and datasets. Verification continues throughout the session, so risk signals can trigger step-up checks or end access before damage spreads.

At a high level, the principles look like this:

• Verify explicitly: Confirm identity and context (who, what device, where, and under what conditions) before allowing access.
• Limit privileges: Provide only the permissions needed for the task, ideally time-bound and revocable.
• Assume a breach: Design access so a stolen login can’t easily cascade into wider compromise.
• Continuously evaluate trust: Reassess risk during sessions using telemetry and behavioral signals.
• Audit and prove accountability: Log access and actions so investigations and compliance reviews don’t rely on guesswork.

External access often starts as a simple exception and quietly becomes permanent—accounts linger, permissions accumulate, and ownership gets fuzzy. Attackers love that kind of drift because a vendor login can be less suspicious than a compromised employee account. It feels efficient—until it doesn’t.

• Uncontrolled lateral movement within enterprise networks: Once inside a flat environment, an intruder can pivot from a single system to adjacent services and sensitive repositories.
• Misuse of privileged access: Over-scoped administrative rights enable high-impact changes, whether through malice, mistake, or stolen credentials.
• Data leakage caused by unauthorized access: Sensitive information may be copied, forwarded, or exfiltrated when access boundaries are unclear or overly broad.
• Challenges in monitoring and securing remote access: Off-network work and unmanaged endpoints make consistent visibility, policy enforcement, and session control harder to maintain.

Managing outside access with zero trust relies on a handful of reinforcing controls that make decisions based on identity, context, and risk. The power comes from the combination: strong verification, narrow permissions, and containment that assumes something will eventually go wrong.

• Identity verification: Ensure contractors and third-parties are authenticated before access, ideally using federated identity and strong authentication flows.
• Role-based access control (RBAC): Grant minimum-necessary permissions to only the resources required, mapped to clear roles and approved use cases.
• Continuous monitoring and trust assessments: Detect and respond to anomalies in real-time by watching session behavior, access patterns, and device signals.
• Granular segmentation: Prevent lateral movement by isolating sensitive systems so access to one application doesn’t imply access to everything nearby.

Zero trust isn’t meant to slow collaboration; it’s meant to make collaboration safer and more predictable. When access becomes precise and measurable, security teams stop chasing spreadsheets and start operating with confidence.

• Enhanced visibility and control over user access: Centralized policy and identity signals clarify who has access, to what, and for how long.
• Minimization of attack surfaces and reduction in the risk of breaches: App-level access reduces exposed pathways and limits what an attacker can reach after initial entry.
• Granular access policies tailored to individual roles: Permissions align to real responsibilities instead of generic “vendor” profiles that grow over time.
• Better compliance with regulatory mandates like GDPR, HIPAA, and PCI DSS: Strong authentication, auditing, and controlled access help satisfy common governance expectations.

A practical rollout follows the lifecycle of third-party engagement: onboarding, access, oversight, and offboarding. Start with visibility, then make policy decisions, then apply technology that enforces those decisions consistently. Momentum matters, so aim for steady progress over “perfect” from day one.

1. Map out contractor and third-party dependencies: Review all external users, applications, and systems requiring access, including who sponsors access and what “done” looks like.
2. Establish identity and governance policies: Enforce least-privileged access and multifactor authentication (MFA), plus clear approval paths and expiration dates for every engagement.
3. Deploy zero trust network access (ZTNA) solutions: Replace VPNs with ZTNA to provide direct, secure application access without exposing broad network connectivity.
4. Monitor activity and enforce compliance: Track user actions, correlate signals across systems, and trigger alerts or automated controls when behavior deviates from expectations.
5. Automate access revocation: Remove access automatically when contracts end, tickets close, or inactivity thresholds are reached, reducing reliance on manual cleanup.

Even strong architecture can weaken if exceptions pile up and nobody revisits them. The healthiest programs treat external access as a living system—reviewed, tuned, and occasionally challenged before an incident forces the issue.

• Regularly audit third-party access permissions and usage: Review entitlements on a schedule, remove dormant accounts, and validate that access still matches current work.
• Use microsegmentation to isolate critical workloads from external users: Contain exposure at the workload level so sensitive environments stay insulated.
• Require step-up authentication and validate identity at every access point: Increase assurance when risk rises, such as unusual locations, new devices, or sensitive requests.
• Ensure contractors use approved devices and secure endpoints: Apply minimum device standards, patching expectations, and endpoint protections where possible.
• Use real-time monitoring tools to detect and block suspicious activity: Pair high-fidelity logging with automated response actions like session termination or policy tightening.

Zscaler secures third-party and contractor access by applying a user- and application-centric zero trust model that replaces broad network reach and always-on tunnels with direct user-to-app connections brokered through the Zscaler Zero Trust Exchange. Instead of forcing VDI, VPN agents, or new dedicated browsers onto unmanaged devices, it enables seamless, agentless access from the user’s browser of choice while continuously verifying identity, context, and risk and enforcing policy per session. 

Our platform approach lets you verify explicitly, limit privileges, assume a breach, and continuously evaluate trust while adding built-in segmentation and integrated data security to reduce exfiltration and lateral movement risks:

• Minimize lateral movement with app segmentation: Direct user-to-app connectivity helps ensure access to one application doesn’t translate into broad network access.
• Reduce data leakage on unmanaged and BYOD endpoints: Zero Trust Browser and fine-grained controls can restrict risky actions like copy/paste, downloads, uploads, and printing.
• Strengthen “never trust, always verify” with real-time policy enforcement: The platform verifies identity, determines destination, assesses risk with AI-driven signals, and enforces access decisions per request.
• Simplify third-party onboarding while lowering cost vs. VDI: Centralized policies on a unified platform streamline governance and can eliminate expensive VDI licensing and operational overhead.

Request a demo to see how Zscaler can deliver secure, agentless third-party access in minutes.