• Posted by: Eng. Donya Bino
• December 14, 2025

API Key Exposure in Frontend Applications

API keys show up in frontend apps more often than they should. Not because developers are careless, but because it’s easy to assume “no one will look.”
They will. And they do.
Anything shipped to a browser or mobile app should be treated as public. That includes JavaScript files, network requests, and embedded configuration values.

Why Frontend API Keys Are Easy to Find
Finding exposed keys doesn’t require hacking skills.
All an attacker needs are:
1. Browser developer tools
2. Network request inspection
3. A quick look at bundled JavaScript
If a key is there, it’s visible. Obfuscation might slow someone down, but it doesn’t protect anything.

How Keys Are Often Exposed
The reason behind this exposure is because it is convenient and not malicious.
Some common reasons for exposed keys are:
1. JavaScript files where keys are hardcoded into the file.
2. Environment variables used for building frontend applications.
3. A mobile application that has the key stored in a configuration file.
4. A client calling a sensitive API from their device directly.
When those keys have been deployed, they are considered public.

What Attacks Can Happen When Keys Are Exposed?
The potential damage caused by an exposed key will depend on what the key gives the attacker access to. Some examples of the types of attacks that can happen as a result of exposed keys are:
1. Use of the company's paid APIs.
2. Getting sensitive information from the company database.
3. Bypassing rate limits associated with the company's applications.
4. Using the exposed key to perform automated scraping or fraud.
In extreme cases, the attack may never be made against the application. The attacker simply uses the key to gain access to other applications they have to hack.

Why “It’s Just a Read-Only Key” Is Risky
Read-only access sounds harmless until it isn’t.
Attackers often use read access to:
1. Map internal systems
2. Collect user data at scale
3. Identify higher-value targets
4. Combine exposed data with other leaks
What starts as “read-only” can support much larger attacks.

How Companies Reduce This Risk
Teams that handle this well follow a few basic rules:
1. Never trust the frontend with secrets
2. Route sensitive API calls through backend services
3. Scope API keys as tightly as possible
4. Apply strict rate limits and monitoring
5. Rotate keys regularly and automatically
These controls don’t slow development. They prevent expensive cleanup later.

A Simple Rule That Actually Works
If an API key must be kept secret, it does not belong in the frontend. That rule catches most design mistakes early and avoids awkward incident reports later.

API key exposure in frontend apps isn’t a rare edge case. It’s one of the most common security issues seen in real environments. The fix isn’t complicated. It just requires treating frontend code for what it is: public by default.