Updated April 12, 2025
Understanding Privilege Escalation in Web Applications
Web applications often handle multiple user roles, each with specific permissions. However, attackers can manipulate access controls to gain unauthorized privileges if improperly secured. This security flaw, known as privilege escalation, comes in two primary forms:
- Horizontal Privilege Escalation – Gaining access to another user’s data at the same privilege level.
- Vertical Privilege Escalation – Gaining elevated permissions, such as administrative access.
Both types pose serious security risks, potentially leading to data breaches, identity theft, or system takeovers. Let’s break down how each works and how to prevent them.
What is Horizontal Privilege Escalation?
Horizontal privilege escalation occurs when an attacker with a standard user account gains unauthorized access to another user’s data or functions. This typically happens due to weak access controls, where the application fails to enforce user-specific restrictions properly.
Example of Horizontal Privilege Escalation
Imagine a banking application where the URL structure includes an account number:
👉 https://bank.com/account?user_id=1001
If a logged-in user manually changes the user_id value to another number—such as:
👉 https://bank.com/account?user_id=1002
—and successfully accesses someone else’s bank details, horizontal privilege escalation has occurred.
How to Prevent It
- Enforce Access Control Checks: Ensure the backend verifies user access before displaying data.
- Use Secure Session Management: Implement tokens tied to user sessions rather than relying on URL parameters.
- Employ Role-Based Access Control (RBAC): Define strict access levels to ensure users can only retrieve their own data.
What is Vertical Privilege Escalation?
Vertical privilege escalation is more severe, as it allows an attacker to increase their permission level—such as upgrading from a regular user to an admin. This often happens when an application relies on client-side validation or improperly secured authentication mechanisms.
Example of Vertical Privilege Escalation
Consider a web application that returns a hidden input field containing a user’s role after login:
<input type="hidden" name="role" value="user">
An attacker can modify this value to:
<input type="hidden" name="role" value="admin">
If the application fails to validate roles properly, the attacker now has administrator privileges, leading to complete control over the system.
How to Prevent It
- Never Trust Client-Side Input: Validate and enforce role permissions on the server-side, not just in the frontend.
- Use Secure Authentication Methods: Implement multi-factor authentication (MFA) and least-privilege principles.
- Monitor for Unusual Activity: Set up security logs and alerts for unauthorized access attempts.
How Web Application Penetration Testing Helps
Privilege escalation vulnerabilities are critical security flaws that must be proactively identified and mitigated. A Web Application Penetration Test simulates real-world attacks to detect:
✅ Unauthorized access attempts
✅ Weak access control mechanisms
✅ Privilege escalation risks
By testing your application from an authenticated user’s perspective, security professionals can uncover vulnerabilities before attackers exploit them.
Final Thoughts
Both horizontal and vertical privilege escalation can lead to devastating security breaches. Implementing secure authentication, access controls, and routine penetration testing is essential for preventing unauthorized access and protecting user data.
Need help securing your web application? Contact our penetration testing experts today to safeguard your platform from privilege escalation threats, and check out OWASP.
Horizontal vs Vertical Privilege Escalation FAQs
Privilege escalation occurs when a user gains access to resources or functions beyond their intended authorization. This typically results from flaws in access control logic, session management, or insecure direct object references (IDOR).
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Horizontal privilege escalation allows a user to access resources or actions assigned to another user with the same privilege level (e.g., a patient viewing another patient’s data).
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Vertical privilege escalation enables a lower-privileged user (like a patient) to gain higher-level access (such as an administrator or clinician role).
Yes. If a user modifies a URL parameter (e.g., /records/123) to access another user’s record (/records/124), and the app does not verify ownership, this constitutes horizontal privilege escalation.
If a regular user discovers a hidden admin-only feature (like /admin/deleteUser) and the system doesn’t restrict access based on roles, they could perform unauthorized admin functions.
Improper privilege controls can expose sensitive patient health information (PHI), violate HIPAA/FDA cybersecurity requirements, and jeopardize patient safety or regulatory approval.
Attackers exploit:
- Insecure IDOR (e.g., URL tampering)
- Weak or absent server-side authorization checks
- Poor session role management
- Client-side role enforcement instead of server-side
Implement access control checks at the server level to ensure users can only access their own resources. Avoid relying solely on user-input identifiers.
Use Role-Based Access Control (RBAC), enforce least privilege, and conduct strict server-side validation before executing any privileged actions.
Security testing tools like Burp Suite, OWASP ZAP, and automated DAST tools can help detect these flaws. Manual testing and code reviews are also essential.
Threat modeling should explicitly include privilege escalation scenarios. FDA-aligned cybersecurity documentation should detail access control strategies and verification testing to demonstrate robust protections.
