The Most Dangerous Bugs Don’t Look Like Security Bugs
One of the worst production issues I’ve seen didn’t involve hacking, malware, or stolen passwords.The system did exactly what we told it to do, not what we intended it to do.
Security failures rarely arrive as dramatic breaches.
More often, they arrive quietly: a user gains access they shouldn’t have, an order ships without payment, or a service exposes data it was never meant to touch.
Nothing crashes.
Nothing alarms.
Everything “works”.Until you look closely.
Many of these incidents come from three design mistakes developers make without realizing they are security decisions: excessive permissions, trusting internal data blindly, and assuming users follow the intended flow
When a service can do more than it should
In most systems, software talks to other software using service accounts.
They exist so applications can read databases, publish messages, or call internal APIs.
The problem starts when those accounts are given permissions based on convenience rather than necessity.
Imagine an order service.
It only needs to create and read orders.
But during development, it is granted broader access — reading users, updating balances, deleting records — simply because it was easier than configuring separate roles.
Nothing breaks.
The service runs perfectly.
Until one day a small vulnerability appears in that service.
The attacker doesn’t just gain control of orders.
They inherit everything the service was allowed to do.
This is the principle of least privilege in practice: systems should be designed assuming compromise is possible.
The damage should stop where the responsibility stops.
When the system lies to itself
Modern systems rarely run as a single application anymore. They are collections of services constantly exchanging information.A payment service updates a status.Another service reads it and grants access.Most of the time, this works.But distributed systems have delays, retries, and partial failures.
One service believes a payment succeeded because it read outdated data from a cache.Another grants access based on that belief.No one hacked anything.
The system trusted a moment that no longer existed.
“Security sometimes fails not because data was stolen, but because data was believed.”
These bugs are hard to detect because the system is internally consistent — just incorrect. They don’t look like errors; they look like legitimate actions.
When flows exist only in the UI
Many applications rely on the interface to enforce order.
You must register before verifying.You must pay before shipping.You must confirm before activating.But interfaces are suggestions, not guarantees.
If the backend does not enforce the same rules, a direct request can skip the intended steps entirely.An order can jump from created to shipped.An account can become active without verification.The system assumes the user followed the path.
The request proves otherwise.
“A process enforced only by screens is not a rule. It is a hope.”
Real systems must validate state transitions explicitly, because APIs can be called in any order.
The shared cause behind all three
These situations appear unrelated: permissions, stale data, skipped steps.Yet they come from the same assumption — that parts of the system will behave correctly. Security problems often emerge not from malicious input but from misplaced confidence.
We trust internal services.We trust flows.We trust timing.
Reality does not.
“Most security issues are trust issues wearing technical clothing.”
Why this matters
Developers tend to associate security with cryptography: hashing, encryption, signatures.But many serious incidents occur before any of those mechanisms matter.Security is not only about protecting secrets.It is about ensuring systems behave safely when expectations fail.A system designed for honest use is fragile.A system designed for unexpected use is resilient.
A small mindset shift
Instead of asking whether something works in the intended path, ask what happens outside it.
What if the service is compromised? What if the data arrives late? What if the step is skipped?
These questions feel pessimistic, but they prevent real incidents.
"Secure systems aren’t the ones that never fail.They are the ones that fail safely.”
Closing thought
Security does not begin when encryption is added.It begins when assumptions are questioned.Many of the most damaging failures don’t involve attackers breaking in.They involve systems quietly allowing what was never meant to happen.
And the only reliable defense against that is not a tool — it is awareness built into design.