What Is Third-Party Access?

Third-Party Access Explained

Granting access to external partners is a business necessity but introduces significant operational complexity. For C-Suite executives, this represents a major supply chain risk. According to Unit 42, attacks involving third-party SaaS applications have surged 3.8x since 2022. Attackers frequently abuse trusted connectivity, such as OAuth tokens and API keys, to move laterally after an initial compromise.

For SOC leaders, the challenge lies in visibility and control. Legacy systems, such as VPNs, often lack the granular policy enforcement needed to restrict vendors to specific tasks. When a vendor connects via VPN, they are essentially placed "inside" the network, which facilitates lateral movement if their account is compromised.

How Third-Party Access Is Exploited

Attackers often succeed by abusing legitimate access rather than relying on novel exploits.

Common Third-Party Attack Paths

1. Credential theft or MFA fatigue
   Vendor credentials may be phished, stolen from logs, or purchased. Push-based MFA may be exploited through fatigue attacks.
2. Session or token theft
   OAuth tokens, cookies, and API keys may be stolen from endpoints, CI/CD systems, or source repositories.
3. Compromised vendor tooling
   If a third-party RMM, help desk, or remote support platform is compromised, attackers may inherit legitimate access at scale.
4. Excess permissions and privilege escalation
   Overly broad access (local admin, domain admin, cloud admin roles) can enable rapid escalation and control.
5. Lateral movement through trusted connections
   After entry, attackers may move from vendor-accessible systems to high-value assets such as identity stores, cloud control planes, or production data.

Types of Third-Party Access

Table 1: Types of Third-Party Access

Third-Party Access vs. Vendor Risk Management

These concepts are related but not identical:

• Vendor Risk Management (VRM): governance processes such as due diligence, contracts, questionnaires, and SLAs
• Third-party access security: technical enforcement such as identity controls, least privilege, monitoring, and revocation

A vendor may “pass” due diligence and still serve as the entry point for a breach if access is poorly controlled.

Use Cases & Real-World Examples

The Unit 42 2026 Global Incident Response Report highlights that the time from initial access to data exfiltration has plummeted to just 72 minutes. This speed necessitates automated, real-time security responses.

• Managed Service Providers (MSPs): MSPs often require privileged access to manage server clusters. Without a centralized portal, tracking their specific actions becomes nearly impossible for compliance auditing.
• SaaS Supply Chain Attacks: Attackers increasingly target the "human interface" through secure browsers to harvest credentials from unmanaged third-party devices.
• Just-in-Time (JIT) Provisioning: Organizations use JIT access to grant temporary permissions only when a vendor needs to perform a specific task, closing the window of opportunity for attackers.

Best Practices for Securing Third-Party Access

1) Inventory all third-party access paths

Effective security starts with visibility. Inventory should include:

• vendor identities (human and non-human)
• access methods (VPN, ZTNA, SSH, SaaS admin)
• permissions, roles, and scopes
• systems and data accessed
• business owner and vendor owner
• start/end dates aligned to contracts

2) Enforce least privilege and least access duration

Controls should include:

• role-based access control (RBAC) with minimal scopes
• removal of standing admin access where feasible
• time-bound access approvals
• per-task provisioning and deprovisioning

3) Require phishing-resistant MFA and strong authentication

Recommended controls include:

• FIDO2/WebAuthn keys for privileged vendor access
• conditional access policies (device posture, location, risk signals)
• blocking legacy authentication methods

4) Use secure access brokering instead of flat network access

Application-specific access is typically safer than broad network access:

• Expose only the required application, not the full network
• Apply per-app policy enforcement
• Capture session-level logs for accountability

This approach significantly reduces opportunities for lateral movement.

5) Apply privileged access controls for vendor administrators

For privileged third-party access, controls commonly include:

• just-in-time (JIT) elevation
• session recording
• command-level restrictions (where feasible)
• vaulting and rotating secrets
• approval workflows and dual control for high-risk actions

6) Manage non-human identities as first-class risk

Key practices include:

• discovering and cataloging API keys, OAuth apps, and service accounts
• limiting scopes to the minimum required
• rotating keys/tokens on a defined cadence
• detecting newly created integrations and unusual API activity
  
  

7) Monitor continuously and alert on vendor anomalies

Monitoring should detect:

• creation of new vendor accounts
• logins from unusual geographies or times
• privilege changes and role grants
• abnormal API call volume or data exports
• repeated authentication failures and excessive MFA prompts
• access to systems outside the approved vendor scope

8) Offboard vendors aggressively

Effective offboarding typically includes:

• disabling accounts and revoking tokens at contract end
• removing group memberships and entitlements
• validating removal through audit logs
• tying deprovisioning to procurement and vendor-management workflows

Third-Party Access Policy Checklist

A baseline policy typically specifies:

• Allowed access methods: ZTNA preferred; VPN restricted; no direct internet-facing RDP
• Authentication requirements: phishing-resistant MFA for privileged access
• Device requirements: managed device enforcement or secure browser/VDI controls
• Approval and ownership: named internal sponsor and vendor sponsor
• Logging: centralized log collection with retention and review requirements
• Data handling: least data access, encryption in transit, export controls
• Incident response: vendor notification timelines and disclosure requirements
• Offboarding SLAs: access removal within defined time windows

Common Mistakes to Avoid

• Shared vendor logins that eliminate accountability
• Permanent admin access “for convenience.”
• VPN access to broad network segments
• Unmanaged OAuth apps and long-lived tokens
• Annual access reviews without continuous verification
• Incomplete vendor offboarding that leaves “ghost access” behind

Third-Party Access FAQs