Broken access control is a common security vulnerability in web applications where the system fails to properly enforce restrictions on what authenticated users are allowed to do or access. This means users might perform actions or view data beyond their intended permissions, often due to flaws in how the application checks and validates requests.
According to security standards, this issue ranks highly among web vulnerabilities because it affects a large percentage of applications and can lead to severe consequences like unauthorized data exposure or modification.
How Broken Access Control Leads to Privilege Escalation
Privilege escalation occurs when an attacker exploits these flaws to gain higher levels of access than they should have. In essence, broken access control acts as the gateway: if the application doesn’t strictly verify a user’s role or permissions for every action, a malicious user can manipulate requests to bypass those checks. This can escalate privileges in ways that allow control over more sensitive parts of the system, potentially leading to full account takeover—where an attacker gains complete control over another user’s account, including changing credentials or accessing personal information.
There are a few key types of privilege escalation tied to access control issues:
• Vertical Privilege Escalation: This happens when a standard user accesses features reserved for higher-privileged roles, like an admin panel. For example, if an application relies on easily tamperable parameters (such as hidden fields or URLs), a user might alter them to impersonate an admin and perform actions like deleting accounts or viewing restricted data.
• Horizontal Privilege Escalation: Here, a user at one level accesses resources belonging to another user at the same level. A common scenario is changing an account identifier in a request to view or edit someone else’s profile, which could reveal sensitive details and enable further compromise.
• Context-Dependent Privilege Escalation: This involves performing actions out of the intended sequence, such as modifying data after a process should have been finalized, exploiting gaps in multi-step workflows.
These escalations can chain together; for instance, horizontal access to another user’s data might uncover credentials that allow vertical escalation to admin rights, ultimately resulting in full takeover of accounts or even the entire system.
Real-World Impact and Examples
In practice, broken access control has been exploited in bug bounty programs and real incidents. For instance, a low-privileged staff account might send a modified request that the system incorrectly processes as coming from a higher role, granting unintended access. This could lead to viewing confidential information, altering business data, or hijacking sessions. Security reports highlight how such vulnerabilities often stem from insecure direct object references (where unique IDs are exposed without verification) or missing checks on API endpoints, making it easier for attackers to force-browse to restricted areas or tamper with metadata like tokens.
The broader impact includes data breaches, financial loss, or operational disruption, as attackers could destroy records, execute unauthorized transactions, or pivot to other systems.
Prevention Strategies
To mitigate these risks, applications should:
• Enforce the principle of least privilege, denying access by default unless explicitly allowed.
• Implement server-side checks for all requests, avoiding reliance on client-side controls that can be bypassed.
• Use consistent access control mechanisms across the app, including for APIs, and log failures for monitoring.
• Validate ownership for data operations and apply rate limiting to prevent automated attacks.
• Regularly test for these issues through unit tests, penetration testing, and code reviews.
By addressing broken access control proactively, organizations can significantly reduce the risk of privilege escalation and account takeovers.