ESV - External Security Verification

Enhanced Definition

ESV, or External Security Verification, is the process by which an application or system component on z/OS delegates the authorization check for a user's access to a resource or function to an external security manager (ESM) like RACF. Instead of implementing its own security logic, the application calls the ESM to make the security decision based on predefined security rules. External Security Verification (ESV) refers to the process by which an application or system component running on z/OS requests a security check from an external security manager (ESM), such as RACF, CA ACF2, or Broadcom Top Secret. Its primary purpose is to determine if a specific user ID has the necessary authorization to access a particular resource or perform an action within the mainframe environment.

Key Characteristics

- Delegated Security: Applications do not contain their own authorization logic; they rely entirely on the ESM for security decisions.
- Centralized Policy Management: All security rules, user profiles, and resource definitions are managed centrally within the ESM's database (e.g., RACF database).
- Standardized Interface: Applications typically use standardized security macros or callable services (e.g., RACROUTE macro in assembler, or equivalent calls in high-level languages) to interact with the ESM.
- Granular Control: ESMs enable highly specific control over who can access what, down to individual datasets, PDS members, CICS transactions, IMS segments, or specific commands.
- Comprehensive Auditing: ESMs provide detailed logging of all access attempts, both successful and failed, facilitating security audits and compliance reporting.
- Flexibility: Security policies can be modified, added, or removed in the ESM without requiring changes, recompilation, or downtime for the applications that rely on them.

Use Cases

- Dataset Access Control: Verifying if a user has appropriate read, write, update, or delete access to a specific MVS dataset or a member within a partitioned dataset (PDS/PDSE).
- CICS Transaction Security: Checking if a user is authorized to execute a particular CICS transaction, access a specific CICS resource (e.g., program, file), or use a terminal.
- IMS Resource Security: Authorizing user access to IMS databases, segments, transactions, or specific commands within an IMS environment.
- System Command Authorization: Determining if a TSO user or an operator is permitted to issue specific z/OS operator commands (e.g., DISPLAY, VARY, CANCEL).
- Program and API Execution: Controlling which users or groups are allowed to execute specific programs, load modules, or access functions exposed by z/OS-based APIs or services.

Related Concepts

ESV is a cornerstone of the External Security Manager (ESM) architecture on z/OS, which includes products like RACF, CA ACF2, and Broadcom Top Secret. It directly leverages the ESM's database to store and evaluate security rules and user profiles. Applications utilize RACROUTE macros or equivalent services to perform ESV, making it a critical component of the overall z/OS security model and ensuring system integrity, data confidentiality, and regulatory compliance.

Best Practices:

Principle of Least Privilege: Grant users and applications only the minimum necessary access required to perform their functions, reducing the attack surface.
Regular Security Audits: Periodically review ESM audit logs for unusual activity, failed access attempts, and potential security violations to detect and respond to threats promptly.
Leverage Generic Profiles: Utilize generic profiles (e.g., DSNAME(PROD.APPL.**)) where appropriate to simplify security administration, reduce the number of explicit profiles, and improve performance.
Implement Role-Based Access Control (RBAC): Group users into security groups (e.g., RACF groups) based on their job functions and assign access rights to these groups, streamlining user management and policy enforcement.
Application-Specific Resource Definitions: Define specific security profiles for application resources (e.g., CICS transactions, IMS databases) rather than relying solely on broader dataset-level security, for finer control.
Test Security Changes Thoroughly: Always test security rule modifications in a non-production environment before deploying them to production to prevent unintended access issues or system outages.