What Is the Broken Access Control Vulnerability?
Broken access control is a security flaw that occurs when an application fails to restrict users' actions based on their permissions. In secure systems, users are assigned roles or privileges, and access control mechanisms ensure that users can only access data or perform tasks appropriate to their authorization level. When these mechanisms are poorly implemented or misconfigured, attackers can exploit the weakness to gain unauthorized access to sensitive resources, modify data, or execute privileged functions.
Such vulnerabilities can arise from both developer oversights and architectural weaknesses. Common causes include missing or incomplete authorization checks, improper use of access control frameworks, or developer assumptions about client-side security. Since access control is enforced on the server side, any lapses in these checks can be difficult to detect through regular user activity but may be quickly discovered and abused by attackers using automated tools or by manipulating requests to bypass controls.
Broken access control is a severe security risk, ranked #1 in the Open Web Application Security (OWASP) Top 10 list of web application vulnerabilities.
In this article:
Confidentiality Breaches
Broken access control can directly lead to breaches of confidentiality, where unauthorized users gain access to private or sensitive information. For example, if an application fails to verify a user's rights before serving up documents, records, or user details, attackers may simply alter a URL or parameter to view data belonging to other users. This can result in exposure of customer records, intellectual property, or personally identifiable information, putting organizations at risk of data leaks or privacy violations.
These breaches can be especially damaging because attackers often exploit automated scripts to harvest large quantities of data undetected. Loss of confidentiality can undermine customer trust, lead to client attrition, and result in contractual or legal liabilities. Organizations dealing with financial, healthcare, or regulated data are particularly vulnerable and stand to suffer significant reputational and operational damage if breaches become public.
Availability Disruption
Attackers exploiting broken access control may not be limited to viewing unauthorized data—they can also disrupt service availability. With elevated privileges, malicious actors can delete critical resources, change system configurations, or execute denial-of-service actions. For example, if an attacker escalates their privileges to those of an administrator, they could lock users out, purge data, or disable an entire service.
Service downtime caused by unauthorized changes can impact business operations and lead to customer churn, lost revenue, and contractual penalties. Furthermore, restoring services after an attack can be resource-intensive, requiring investigation, remediation, and sometimes, negotiation with the attacker. Ensuring reliable access control is critical for maintaining uptime and operational continuity in any digital service.
Regulatory and Compliance Risks
Many industries are governed by regulations—such as GDPR, HIPAA, or PCI DSS—that require strict control over who can access specific kinds of data and functions. A breakdown in access control can easily translate into compliance violations, triggering audits, penalties, or even class-action lawsuits. Regulators expect organizations to demonstrate effective controls and swift remediation capabilities, making broken access control a direct compliance liability.
In addition, failure to comply with regulations can restrict an organization’s ability to operate in certain markets or handle sensitive information. For example, violating HIPAA can bar an organization from working with health records, and GDPR fines can reach up to 4% of annual global turnover. Demonstrating strong access control methods is not just about risk mitigation but is also essential for securing business partnerships and certifications.
Reputational and Financial Damage
Organizations compromised by broken access control often face significant reputational loss. News of unauthorized access spreads rapidly, leading to erosion of customer confidence and damage to brand credibility. Victims face negative publicity, regulatory scrutiny, and the prospect of expensive incident response campaigns, which can further erode trust with stakeholders and partners.
The financial impact can be severe, encompassing direct losses from fraud or theft, costs related to incident recovery, compensation to affected users, and legal expenses. Indirect losses might include lost business opportunities, increased insurance premiums, and a decline in stock value. For many organizations, especially those with digital-first business models, the damage from a single breach can be existential.
1. Insecure Direct Object References (IDOR)
IDOR flaws occur when an application exposes internal implementation objects—such as files, database records, or URLs—without adequately verifying the user’s authorization. For example, if user A can access their document by visiting /documents/1234 and simply changing the URL to /documents/5678 allows them to access user B’s private document, the system is vulnerable to IDOR. These vulnerabilities often result from developers assuming client-side controls are sufficient or neglecting to verify each request server-side.
IDOR attacks are easily exploitable because attackers can increment, enumerate, or guess resource identifiers and retrieve sensitive data or perform unauthorized operations. Automated tools can further scale these attacks. Preventing IDOR requires strict checks before returning any object tied to a user session—never trusting user input to define access scope.
2. URL and Parameter Manipulation
URL and parameter manipulation vulnerabilities allow attackers to change request data, such as query parameters, form fields, or HTTP headers, to gain unauthorized access. Web applications frequently pass resource identifiers or privilege flags in URLs and parameters, sometimes assuming these values won’t be tampered with. Attackers can modify these values to bypass restrictions, escalate privileges, or view and modify data.
These issues are common in applications that rely heavily on client-side controls or fail to revalidate parameters on the server. Failing to tie access decisions to the authenticated user's current privileges exposes avenues for horizontal and vertical privilege escalation. Proper server-side validation, use of indirect references, and parameter whitelisting help mitigate these flaws.
3. Access Control Flaws in Multi-Step Processes
Complex workflows involving multiple steps—such as financial transactions, account setup, or configuration changes—can harbor access control gaps if checks are only applied at the beginning or end of a process. Attackers exploit this by skipping, replaying, or mishandling intermediate steps to bypass security controls or gain unauthorized access.
Applications that rely on front-end controls to enforce sequence or ownership are particularly vulnerable. Attackers use tools like intercepting proxies to alter or replay requests out of order. Ensuring robust, server-side validation of user privileges at each workflow step is essential, as is assigning unique tokens or state tracking to prevent process manipulation.
4. Misconfigured Access Control Policies
Access control policies define what actions users can take and which resources they can access. When these policies are misconfigured—such as by assigning overly permissive defaults or incorrectly mapping roles—users may gain access above their intended level. This often happens in platforms with complex permission matrices or decentralized administration, where configurations drift over time.
Policy misconfigurations can occur during development, deployment, or maintenance, especially if proper change management procedures are lacking. Auditing configurations regularly, applying secure defaults, and using infrastructure-as-code tools for policy management help reduce the risk. Transparent, centralized policy administration is key for scaling access control securely.
5. Over-Privileged Accounts and Weak Role Assignments
Giving users more privileges than necessary increases the attack surface. Over-privileged accounts may exist due to convenience, lack of granular roles, or failure to update privileges as users change roles or leave the organization. Weak role assignment—such as assigning most users to powerful admin roles—makes it easier for attackers to compromise critical systems if any account is breached.
Periodic access reviews, ensuring granular roles, and immediate revocation of unnecessary privileges are crucial for minimizing risk. Automated onboarding/offboarding processes and role-based access designs ensure privileges align with actual job responsibilities. Principle of least privilege should be enforced across systems to keep access footprints as small as possible.
Related content: Read our guide to application security tools.
Jeremie Ohayon
Jeremie Ohayon is a Senior Product Manager at Radware with 20 years of experience in application security and cybersecurity. Jeremie holds a Master's degree in Telecommunications, and has an abiding passion for technology and a deep understanding of the cybersecurity industry. Jeremie thrives on human exchanges and strives for excellence in a multicultural environment to create innovative cybersecurity solutions.
Tips from the Expert:
In my experience, here are tips that can help you better defend against broken access control vulnerabilities:
1. Use deny-by-default access control models: Instead of starting with broad access and narrowing it down, design your access control logic to explicitly deny all actions unless a permission is granted. This approach forces precise control and prevents accidental exposure due to missing rules.
2. Instrument access control checks with telemetry: Embed logging and metrics into every access control decision. This lets you monitor real-time access attempts, spot unusual patterns (like a user requesting 1000 different resources in a short time), and detect abuse or probing before it escalates.
3. Scan for 'access drift' using automated tools: Use policy-as-code tools (e.g., Open Policy Agent, Rego) to define access rules and periodically scan for misalignments between intended access and actual permissions across systems. Automating this helps catch unintended privilege escalation or overly broad grants over time.
4. Apply fine-grained access tags at the resource level: Move beyond user-based permissions and implement resource tagging (e.g., owner ID, department, sensitivity level) directly in your data models. Then enforce access logic using both user attributes and resource tags for contextual authorization.
5. Run 'role explosion' simulations before deployment: In complex RBAC/ABAC systems, simulate how many roles or policies will be created based on current rules. If your model leads to hundreds or thousands of unique combinations, refactor—this complexity often leads to maintenance errors and misconfigurations.
XZ Utils Backdoor
In early 2024, the open-source file compression utility XZ Utils was discovered to contain a backdoor after a malicious contributor introduced code that subverted access controls at the system level. Exploiting trust in open-source governance, the attacker inserted logic permitting unauthorized remote access to affected Linux distributions. The attack potentially affected millions of systems before being detected by researchers.
This incident illustrates that access control vulnerabilities are not limited to web applications—they can exist deep within system-level or supply chain components. It underscores the need for rigorous code review, continuous monitoring, and supply chain security practices in both open-source and commercial software projects.
MOVEit Data Breach
In 2023, the MOVEit file transfer platform made headlines after attackers exploited broken access controls to access sensitive files belonging to thousands of organizations. Attackers leveraged vulnerabilities in the application to execute unauthorized SQL queries, bypassing authentication and authorization checks. This allowed them to exfiltrate large volumes of customer, financial, and health-related information, affecting businesses, educational institutions, and government agencies around the globe.
The breach showcased the cascading effects of broken access controls on widely used third-party software. The scope of impact was amplified because MOVEit customers often transferred highly sensitive data through the platform. The aftermath included lawsuits, regulatory investigations, and significant operational disruptions for many organizations dependent on MOVEit for secure file transfers.
U.S. Department of State Email Breach
In 2023, the U.S. Department of State suffered an email breach attributed to attackers exploiting broken access controls in cloud-based email systems. By circumventing inadequate access policies, attackers gained unauthorized access to thousands of government email accounts, including those of officials working on sensitive diplomatic and defense matters. The breach exposed sensitive correspondence and heightened concerns about the security of government communications.
This incident highlighted the dangers organizations face when access controls are not rigorously enforced or reviewed, especially in environments relying on cloud-based services and third-party platforms. The attack led to policy reviews, increased security audits, and renewed focus on access control mechanisms within critical infrastructure and government agencies.
Spring Security Broken Access Control
In 2022, a critical vulnerability was discovered in Spring Security, a widely used Java security framework. The flaw allowed attackers to bypass method-level security checks in web applications leveraging specific configurations. Exploiting this weakness, unauthorized users could access endpoints meant to be protected, perform privileged actions, or view sensitive information, depending on implementation details.
The case demonstrated that even trusted, well-maintained frameworks are not immune from broken access control risks. It also emphasized the responsibility of developers to stay updated with security advisories, patch dependencies promptly, and regularly audit custom security logic layered on top of popular libraries.
1. Apply the principle of least privilege
Assign users only the permissions necessary to perform their specific job functions. Avoid using shared accounts or giving users administrative rights unless explicitly required. Excessive privileges increase the risk that an attacker—or even a legitimate user—can access sensitive systems or data beyond their role.
Limit access to high-risk operations such as user management, system configuration, or financial transactions. For example, customer support staff should not be able to modify billing records unless such tasks fall under their responsibility. Implement temporary privilege elevation mechanisms (e.g., just-in-time access) when elevated rights are needed for short periods.
Automate privilege provisioning and revocation during onboarding, role changes, or offboarding. Integrate these workflows with your identity and access management (IAM) systems to prevent privilege creep. Least privilege should apply not just to users, but also to applications, service accounts, and third-party integrations.
2. Enforce strong role-based and attribute-based access controls
Role-based access control (RBAC) organizes permissions based on job functions. Design roles carefully—avoid assigning users to overly broad roles such as "admin" or "superuser" unless absolutely required. Use a separation of duties model to prevent conflict-prone roles (e.g., no single user should both approve and initiate payments).
Attribute-based access control (ABAC) adds further granularity by using contextual data—such as user department, device type, geolocation, or time of access—to make access decisions. For example, a sales manager might be allowed to access customer data only during work hours and only from corporate devices.
ABAC is particularly useful in large or dynamic environments like cloud infrastructures, where role hierarchies may be insufficient to model complex access needs. Implement centralized policy enforcement points (PEPs) and policy decision points (PDPs) to manage ABAC policies efficiently across services.
3. Secure session and token management
Sessions must be uniquely identifiable, tied to authenticated users, and expire appropriately. Use secure, unpredictable session IDs that are regenerated after login and privilege elevation. Store session data only on the server side to prevent tampering.
Use short token lifespans and refresh tokens to minimize risk if a token is intercepted. For example, OAuth 2.0 access tokens should expire quickly, while refresh tokens should be bound to client and IP to reduce misuse. Implement token revocation lists or introspection endpoints to disable tokens when needed.
Mitigate session hijacking by monitoring for anomalies like IP or device changes and automatically invalidating suspicious sessions. Implement SameSite cookie flags, secure cookie attributes, and HTTP-only flags to protect session cookies from cross-site attacks. Always use TLS to encrypt session and token transmission.
4. Conduct regular audits and access reviews
Access controls must be continuously verified to ensure they remain effective as business processes and personnel change. Schedule regular reviews of user permissions, group memberships, role assignments, and system access logs. Involve system owners and managers in reviewing access for their teams.
Monitor for dormant accounts, unused privileges, and unauthorized role escalations. Use tools like AWS IAM Access Analyzer or Azure Privileged Identity Management to detect excessive permissions. Correlate access logs with authentication events to identify privilege abuse or abnormal usage patterns.
Implement least access alerting—flagging any deviation from expected access behavior. For example, if a marketing user suddenly accesses engineering resources, this should trigger an alert. Document and follow up on every audit finding to ensure continuous improvement in access governance.
5. Implement multi-factor authentication
Multi-factor authentication significantly raises the security bar by requiring at least two of the following: something the user knows (password), something the user has (authenticator app, hardware token), and something the user is (through biometrics).
Mandate MFA for all administrator accounts, remote access methods, and any access to critical systems or sensitive data. For cloud environments, enforce MFA through identity providers or directory services. Choose phishing-resistant options like FIDO2 hardware tokens or TOTP-based apps over SMS-based MFA.
Integrate MFA into your access control policies. For example, require step-up authentication for sensitive operations (e.g., fund transfers, permission changes) even if the user is already logged in. Ensure MFA systems are resilient, with backup methods and recovery workflows that don’t compromise security.
MFA complements access control by adding an independent layer of verification, making unauthorized access more difficult even when credentials are compromised.