Added release notes and version entries for 2025.21.1

Author: GitHub Actions

website/blog/2025-05-26-Release-0.md

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+---
+author: meshcloud
+title: Release 2025.21.1
+---
+
+Release period: 2025-05-22 to 2025-05-26
+
+This release includes the following issues:
+* Fix Access Restriction of Service Binding Endpoint
+* Fix Building Blocks List in Admin Definition Control Plane
+* Fix User Permissions Input for Building Blocks
+* Fix Building Block Input Regex Validation Not Saved
+<!--truncate-->
+
+## Ticket Details
+### Fix Access Restriction of Service Binding Endpoint
+**Audience:** User<br>
+
+#### Description
+We have fixed a security vulnerability where workspace members 
+could access the service bindings of service instances in 
+projects of the same workspace they were not assigned to. 
+This update ensures that service binding access is now strictly 
+limited to members explicitly assigned to the relevant project, 
+strengthening project-level isolation and access control.
+
+### Fix Building Blocks List in Admin Definition Control Plane
+**Audience:** Partner<br>
+
+#### Description
+Previously, the 'Building Blocks' tab in the building block definition control plane displayed incorrect results, showing all building block definitions. This has now been fixed. The tab now correctly shows only the building blocks related to the building block definition.
+
+### Fix User Permissions Input for Building Blocks
+**Audience:** User, Partner, Operator<br>
+
+#### Description
+Building Blocks on tenant level support 'User Permissions' as input.
+The underlying type has recently been changed to be 'CODE' instead of 'LIST'.
+This led to problems during execution of existing building blocks. 
+We fixed these problems so meshStack is now capable of handling older versions
+of building blocks that still use the 'User Permissions' input with the deprecated 'LIST' type.
+
+### Fix Building Block Input Regex Validation Not Saved
+**Audience:** User, Customer<br>
+
+#### Description
+A regression from a recent rework of the building block definition form introduced a problem 
+that could prevent proper editing and saving of an existing regex validation for an input 
+field. This problem has been fixed.
+