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Last updated: April 29, 2026
Trust boundaries are where one component trusts data from another. Each crossing is a place to validate. Most apps have at least 5:
Trust boundaries are where one component trusts data from another. Each crossing is a place to validate. Most apps have at least 5:
- Browser to server (the obvious one — input validation)
- Server to database (parameterised queries)
- Server to upstream API (output validation, response-content trust)
- Server to cache (cache-key collisions, deserialisation)
- Server to message queue (event payload validation)
Plus: server to file system, server to logs, server to embedded resource. Bugs across each.
The mindset: name each boundary in your service. For each, name the validation. Gaps = bugs.
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