Architecting Trust: 5 Patterns to Prevent Insider Threats

"Quis custodiet ipsos custodes?" — Who watches the watchmen?

In the world of software, developers are the watchmen. We hold the keys to the kingdom. We write the logic that moves money, approves loans, and deletes users. But with great power comes the potential for... well, "creative" adjustments to one's own benefit.

It’s not just about malicious intent. It’s about risk. If a single developer can modify the production database to add a zero to their bank balance without anyone noticing, your architecture has failed. "Don't do that" is not a security policy.

Here are 5 architectural patterns to ensure that your system is resilient to insider threats and internal fraud.

This is the holy grail of financial systems. The core rule is simple: The person who initiates an action cannot be the one who approves it.

A developer writes a script to "fix" a data issue. The script also happens to credit their account with $500. They run it. Profit.

Separate the Maker (Initiator) from the Checker (Approver).

In this architecture, the developer has the permission to Propose, but not to Execute. The Team Lead has the permission to Approve, but not to Propose. Collusion is required for fraud, doubling the difficulty.

You’ve heard it before, but do you practice it?

Your application needs to read and write to the database. So you give the application's DB user db_owner or ALL PRIVILEGES. A developer gains access to the config credentials and now has full control over the DB structure, including DROP TABLE.

Granular permissions. The application user should only have exactly what it needs, and no more.

• Application User: SELECT, INSERT, UPDATE (only on specific tables). No DELETE? Ideally, yes (see Soft Deletes). Definitely no DROP or ALTER.
• Developer User: SELECT (Read-only access to production).

If a developer needs to modify data, they must use a tool or API that enforces business logic (and logs it), rather than raw SQL access.

Traditional databases store the current state. Event Sourcing stores the history.

If I run UPDATE balance SET amount = 1000 WHERE user_id = 'me', the previous value is gone. Traces can be wiped.

Don't store the state. Store the events.

Instead of a Balance column, you have a Transactions table. The balance is simply the sum of all transactions.

If a "creative" developer tries to inject a +5000 adjustment, it appears as a distinct row. They cannot simply "edit" the total. To calculate the balance, the system replays the events. If that +5000 lacks a valid Origin (like a Payment Gateway ID), the replay logic can flag it as invalid.

You cannot change the past; you can only append to the future.

WORM stands for Write Once, Read Many.

A developer changes a record and then deletes the corresponding line in the log file to cover their tracks.

Ship logs immediately to a storage medium that does not support modification or deletion for a set period.

• AWS S3 Object Lock: Places a "retention period" on objects. Even the root user cannot delete them until the timer expires.
• Blockchain-like structures: Each log entry contains a cryptographic hash of the previous entry. Modifying an old log breaks the chain, alerting the system immediately.

EXPANDCOPY
text
Log Entry N:
{
  "timestamp": "2026-01-23T12:00:00Z",
  "action": "UPDATE_USER",
  "actor": "dev_john",
  "prev_hash": "a1b2c3d4..." // Hash of Entry N-1
}

This is the organizational counterpart to Maker-Checker.

The same person writes the code, tests the code, deploys the code, and manages the database. This is common in startups ("The Full Stack Hero"), but it’s a security nightmare.

Split the roles.

• Dev: Writes code.
• Ops/SRE: Manages deployment and infrastructure.
• DBA: Manages data integrity.

If a developer wants to deploy a backdoor:

1. They write it.
2. Code Review: Peer catches it.
3. CI/CD: Automated tests run on a separate server.
4. Ops: Deploys the artifact (the developer doesn't have SSH access to Prod).

By breaking the chain of custody, you ensure that no single individual has the complete keys to the kingdom.

Trust is good. Architecture is better. By implementing these patterns, you protect not just the company, but the developers themselves. When the system is secure by design, no one has to look over their shoulder, wondering if they could break the rules. They simply can't.