I'm Kanishka Khandelwal, an Application Security Engineer and security researcher focused on web & API security testing, bug bounty hunting, and vulnerability research. In this OWASP Top 10 series, I'll be sharing practical real-world attack techniques, exploitation methods, and mitigation strategies to help understand modern web security deeply.

Introduction

Modern web applications are built around trust boundaries.

Applications trust: users, sessions, roles, APIs, frontend restrictions, object identifiers, backend authorization logic, and internal services.

Broken Access Control occurs when these trust assumptions fail.

According to OWASP, Broken Access Control is one of the most dangerous vulnerabilities in modern applications because it directly affects authorization — the mechanism responsible for deciding who can access what.

Unlike vulnerabilities that rely heavily on payloads or memory corruption, Broken Access Control vulnerabilities often arise from:

• missing authorization checks,
• hidden functionality exposed through APIs
• weak tenant isolation,
• business logic mistakes,
• insecure workflows,
• role inheritance issues,
• and inconsistent backend validation.

The dangerous part is:

attackers often do not need to "hack" the application.

Sometimes they simply request resources or functionality they were never supposed to access.

And if the backend fails to validate permissions correctly, the application becomes vulnerable.

Understanding Access Control

Access control defines permissions and restrictions inside an application.

Think about a corporate office building.

Different people have different access cards:

• Cleaning staff can access maintenance areas.
• Employees can access office floors.
• Finance teams can access financial departments.
• Admins can access restricted infrastructure rooms.
• CEOs may have unrestricted access.

Now imagine:

• a cleaning staff card suddenly opens the finance department,
• an employee accesses the CEO office,
• or visitors can directly enter internal server rooms.

That is essentially what Broken Access Control looks like in web applications.

Applications constantly answer questions like:

• Can this user access admin functionality?
• Can this user modify another user's data?
• Can internal APIs be accessed externally?
• Can support staff perform admin actions?
• Can premium-only features be accessed for free?
• Can users bypass workflow restrictions?

Broken Access Control occurs when the application fails to enforce these restrictions properly.

Types of Access Control

1. Vertical Access Control

Vertical access control restricts access based on privilege levels.

Example roles:

• normal user
• moderator
• admin
• super admin

Example:

GET /admin/audit-logs

If a standard user successfully accesses this endpoint: vertical access control is broken.

2. Horizontal Access Control

Horizontal access control restricts access between users with the same privilege level.

Example: User A accesses:

GET /api/profile/9281

Attacker changes:

GET /api/profile/9282

If another user's profile is returned: the application suffers from IDOR (Insecure Direct Object Reference).

3. Context-Dependent Access Control

Access depends on application state or workflow.

Examples:

• skipping payment flows,
• downloading premium content without subscription,
• bypassing KYC verification,
• canceling orders after shipment,
• abusing refund workflows.

Example:

POST /api/order/cancel

An application may allow cancellation only before shipping.

But if attackers manipulate the workflow state: shipped products may still get refunded.

Why Broken Access Control Is So Dangerous

Broken Access Control vulnerabilities frequently lead to:

• account takeover,
• sensitive data exposure,
• admin access,
• internal API compromise,
• cloud resource exposure,
• tenant isolation failure,
• financial abuse,
• and business logic exploitation.

Unlike reflected vulnerabilities, authorization flaws often expose:

• real customer records,
• invoices,
• payroll data,
• internal dashboards,
• cloud infrastructure,
• private support systems.

These vulnerabilities are especially dangerous because:

the application itself performs the unauthorized action.

Common Causes

1. Frontend-Only Restrictions

Applications hide sensitive functionality in the frontend but fail to secure the backend.

Example:

if(user.role !== "admin"){
   hideAdminMenu()
}

Attackers directly request:

GET /api/admin/export-users

because the backend never validates authorization.2. Hidden Mobile APIs

Developers often assume users cannot inspect mobile applications.

But attackers reverse engineer APKs and discover hidden APIs like:

/api/mobile/internal/debug/users

If backend authorization is weak:

• attackers access internal mobile functionality.3. Business Logic Access Control Failure

An e-commerce application hides employee discount coupons from regular users.

Frontend restriction:

hideEmployeeCoupons()

But attackers manually submit:

POST /api/coupon/apply
{
   "coupon":"EMPLOYEE100"
}

If the backend never validates employee status: unauthorized discounts become possible.

4. JWT Authorization Misconfigurations

Applications trust JWT claims without verifying:

• signatures,
• token integrity,
• role validation.

Example:

{
   "role":"admin"
}

If unsigned tokens are accepted:

• attackers escalate privileges.

5. Weak Tenant Isolation

Multi-tenant SaaS applications often rely on:

• tenant IDs,
• workspace IDs,
• organization identifiers.

Example:

GET /api/tenant/alpha-company/reports

If attackers replace:

alpha-company → victim-company

and data becomes accessible: tenant isolation is broken.

Modern Attack Surface

Broken Access Control is no longer limited to web pages. Modern targets include:

• REST APIs,
• GraphQL APIs,
• mobile applications,
• cloud dashboards,
• WebSocket servers,
• microservices,
• internal APIs,
• object storage systems,
• CDN resources.

Many modern applications secure frontend interfaces while exposing weakly protected backend APIs.

Recon Methodology Used by Attackers

1. Endpoint Enumeration

Attackers search for: undocumented APIs, admin routes, hidden dashboards, beta features, staging endpoints.

Tools:

• Burp Suite
• ffuf
• Caido
• katana

Example:

ffuf -u https://target.com/FUZZ -w wordlist.txt

2. JavaScript Recon

Modern applications expose hidden functionality inside JavaScript bundles.

Attackers search for:

• admin APIs,
• internal endpoints,
• feature flags,
• role names,
• hidden parameters.

Example:

/api/internal/export-financial-report

3. Feature Flag Abuse

Applications often deploy hidden beta features.

Frontend disables access:

feature_enabled = false

But backend endpoints remain accessible:

GET /api/beta/admin/reports

Attackers directly abuse hidden functionality.

4. WebSocket Authorization Testing

Modern applications use WebSockets for:

• chats,
• dashboards,
• support systems,
• notifications.

Example:

{
   "action":"join_room",
   "room":"executive-board"
}

If authorization checks are missing: attackers join restricted communication channels.

Real-World Exploitation Workflow

A common exploitation flow looks like:

1. Register low-privilege account
2. Enumerate APIs
3. Analyze JavaScript files
4. Discover hidden functionality
5. Manipulate identifiers
6. Test role boundaries
7. Abuse workflow logic
8. Escalate privileges
9. Access sensitive resources

IDOR — One Form of Broken Access Control

IDOR occurs when applications expose internal object references without validating ownership.

Example:

GET /api/document/8821

If attackers can access another user's confidential document: authorization validation is broken.

But modern Broken Access Control vulnerabilities extend far beyond simple IDORs.

Advanced Broken Access Control Scenarios

1. Support Staff Privilege Escalation

A support employee can normally:

• reset passwords,
• manage tickets,
• verify accounts.

But backend APIs accidentally allow:

POST /api/admin/promote-user

because support roles inherited admin permissions internally.

Result:

• support staff becomes administrator.

2. Cloud Storage Authorization Failure

Applications generate predictable cloud storage URLs:

https://storage.example.com/reports/q1-finance.pdf

If storage buckets lack proper access control:

• attackers enumerate confidential reports directly.

3. Premium Feature Bypass

Streaming platform:

• hides premium videos from free users.

Attackers directly access:

/cdn/premium/masterclass.mp4

because CDN authorization is missing.

4. Race Condition Authorization Bypass

Banking application allows one withdrawal request at a time:

POST /api/withdraw

Attackers send 20 simultaneous requests.

Due to race conditions:

• balance validation fails,
• multiple withdrawals succeed.

5. OAuth Scope Misconfiguration

Application validates only token presence:

Authorization: Bearer token

but fails to validate scopes properly.

Low-privileged OAuth tokens access:

/api/admin/export-users

resulting in privilege escalation.

GraphQL Access Control Issues

GraphQL APIs frequently suffer from:

• excessive data exposure,
• resolver-level authorization flaws,
• field-level access control failures.

Example:

query{
  employee(id:"17"){
     name
     salary
     performance_notes
     termination_reason
  }
}

Employees may be authorized to view:

• names,
• departments.

But not:

• salaries,
• HR notes,
• termination records.

If field-level authorization is missing:

• sensitive internal information leaks.

Cloud & Microservice Risks

Modern architectures rely heavily on internal trust.

Common issues include:

• trusted internal headers,
• insecure API gateways,
• exposed Kubernetes dashboards,
• weak service-to-service authentication,
• misconfigured RBAC systems.

Example:

X-Internal-User: admin

If internal headers are trusted externally:

• attackers impersonate privileged services.

Tools Used by Security Researchers

Burp Suite

Used for: authorization testing, request replay, parameter manipulation, session analysis.

ffuf

Used for: endpoint discovery, hidden route enumeration, forced browsing.

Caido

Useful for: API testing, workflow analysis, replay attacks.

jwt_tool

Used for: JWT testing, signature validation, role manipulation checks.

Famous Real-World Cases

Facebook Business Logic & Access Control Bugs

Researchers discovered multiple authorization flaws involving:

• page management,
• business manager permissions,
• asset ownership validation.

These vulnerabilities enabled:

• unauthorized business actions,
• privilege escalation,
• restricted asset access.

Microsoft Power Apps Data Exposure

Improper backend authorization exposed millions of records publicly.

Exposed information included:

• vaccination data,
• employee records,
• government datasets.

Root cause:

• weak access control enforcement.

Mitigation Strategies

1. Enforce Authorization Server-Side

Never trust:

• frontend restrictions,
• hidden buttons,
• client-side checks,
• disabled UI elements.

Always validate authorization on the backend:

if current_user.id != resource.owner:
    deny_access()

2. Implement Proper RBAC

Use centralized authorization systems.

Avoid:

• scattered permission checks,
• inconsistent access logic,
• inherited role confusion.

3. Deny By Default

Applications should reject access unless explicitly allowed.

4. Validate Every Request

Every request should validate:

• user identity,
• ownership,
• roles,
• tenant boundaries,
• workflow state.

5. Secure Internal APIs

Never assume:

• internal APIs are unreachable,
• mobile endpoints remain hidden,
• internal headers cannot be spoofed.

Detection & Blue Team Perspective

Security teams should monitor:

• abnormal object enumeration,
• unusual role changes,
• tenant switching behavior,
• API traversal patterns,
• excessive 403 responses,
• hidden endpoint access attempts.

SIEM detections may include:

• unauthorized admin API access,
• sequential identifier requests,
• suspicious WebSocket subscriptions,
• repeated workflow bypass attempts.

Bug Bounty Researcher Notes

Broken Access Control remains one of the highest-value vulnerability categories in bug bounty programs.

Researchers actively hunt for:

• IDOR,
• hidden APIs,
• GraphQL authorization flaws,
• tenant escapes,
• support privilege escalation,
• feature flag abuse,
• OAuth misconfigurations,
• cloud storage exposure.

Strong reports usually contain:

• clear privilege boundaries,
• real business impact,
• reproducible exploitation,
• proof of unauthorized actions.

Labs & Practice Resources

PortSwigger Web Security Academy

Excellent labs covering: IDOR, privilege escalation, access control bypass, business logic abuse.

OWASP Juice Shop

Modern vulnerable application for practicing security testing.

DVWA

Good environment for learning authorization flaws and web vulnerabilities.

Final Thoughts

Broken Access Control is dangerous because applications frequently assume:

authenticated users are trustworthy users.

But authentication alone does not guarantee authorization.

Modern attackers abuse: hidden APIs, workflow flaws, cloud trust assumptions, internal services, weak tenant isolation, feature flags, business logic mistakes, and inconsistent backend validation.

As applications become increasingly API-driven and cloud-native, Broken Access Control continues to remain one of the most impactful vulnerabilities in modern security testing.

Thank You for Reading

I'll be covering the entire OWASP Top 10 deeply with: advanced exploitation techniques, real-world attack methodology, bug bounty insights, mitigation strategies, practical case studies, and modern application security concepts.

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Kanishka Khandelwal on LinkedIn

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