OWASP Top 10 API Security Risks – 2023: API3:2023 – Broken Object Property Level Authorisation
Modern software systems heavily rely on APIs (Application Programming Interfaces) to facilitate communication between services, making APIs a prime target for attackers. Among the OWASP API Security Top 10 Risks for 2023, API3:2023 – Broken Object Property Level Authorisation stands out due to its unique challenges in ensuring fine-grained authorisation control. This risk amalgamates two prior categories from 2019—Excessive Data Exposure and Mass Assignment—and underscores the critical need for robust authorisation validation at the object property level.
This blog post delves deeply into API3:2023, exploring its root causes, real-world implications, and mitigation strategies tailored for software developers and penetration testers.
Understanding API3:2023 – Broken Object Property Level Authorisation
API3:2023 represents a nuanced security challenge where improper or absent authorisation checks allow attackers to access or manipulate sensitive properties of an object within an API. Unlike broader access control issues, this risk focuses specifically on granular authorisation, which determines the visibility or modifiability of individual object properties.
Key Components of API3:2023
- Excessive Data Exposure
APIs often expose more data than necessary. For instance, when an API endpoint returns a user profile, it might inadvertently include sensitive fields like password_hash or is_admin. - Mass Assignment
This occurs when attackers exploit loosely validated input to modify object properties beyond their authorised scope. For example, submitting unexpected properties in a JSON payload could override fields like role or access_level. - Root Cause
The common denominator is inadequate validation at the object property level. This deficiency occurs when developers assume that client-side applications will only request or modify allowed properties, leading to trust-based security models prone to exploitation.
Real-World Examples
Case 1: Exposing Sensitive Information
A payment API for a ride-sharing app unintentionally exposes sensitive user details such as payment methods and saved addresses when returning a user_profile object. Attackers exploiting excessive data exposure could scrape this information to commit fraud or sell it on the dark web.
Case 2: Privilege Escalation via Mass Assignment
Consider a SaaS application where users can update their profiles using a PATCH endpoint:
json
{
“email”: “[email protected]”,
“role”: “admin”
}
If the backend fails to validate the role field, a malicious user could escalate their privileges to administrator, compromising the entire system.
Cyber incidents related to API3:2023 – Broken Object Property Level Authorisation are often underreported but can have devastating consequences for businesses. Here are notable real-world examples and hypothetical scenarios that demonstrate the risks associated with this vulnerability:
While API3:2023 – Broken Object Property Level Authorisation is a relatively new category within the OWASP Top 10 for API security risks, its core issue—improper or absent authorisation checks at the object property level—has led to several cyber incidents in recent years.
Real-World Cyber Incidents
1. Facebook Data Breach (2019)
While predating the 2023 classification, Facebook’s API design flaws serve as a cautionary tale. Developers inadvertently exposed excessive data through API endpoints, allowing attackers to scrape details from user profiles. This breach highlighted the risks of excessive data exposure due to insufficient object property-level validation.
Impact:
- Over 500 million user records were exposed.
- Legal and regulatory actions under GDPR, resulting in fines.
- Erosion of public trust.
2. Shopify Partner API Misuse (2020)
A rogue app developer exploited Shopify’s Partner API to retrieve excessive user data beyond what was necessary for the app’s operation. This incident involved excessive data exposure and underscored the need for fine-grained authorisation.
Impact:
- Compromised merchant and customer information.
- Financial losses for affected businesses.
3. Twitter API Privilege Escalation (2021)
An attacker manipulated Twitter’s API using unauthorised properties in a payload to escalate their account privileges. This type of attack mirrors mass assignment vulnerabilities.
Impact:
- Multiple high-profile accounts were compromised.
- Hackers propagated cryptocurrency scams, leading to financial fraud.
4. T-Mobile API Breach (2021)
In 2021, T-Mobile suffered a major data breach after a misconfigured API exposed sensitive customer data. Attackers were able to exploit the API to retrieve account data, including phone numbers, names, and billing information. The root cause was improper authorisation checks at the object property level, which allowed unauthorised users to access more information than intended.
Impact:
- 40 million customers were affected, with personal data exposed.
- Financial repercussions: The company faced regulatory fines and legal costs.
- Reputational damage: Trust in T-Mobile was severely impacted, with customers moving to competitors.
Lessons Learned:
- The breach was partly due to excessive data exposure and a lack of fine-grained authorisation, which allowed unauthorised access to customer information. This highlights the need for strict object-level authorisation to prevent unauthorised data access.
5. Uber API Incident (2022)
In 2022, a vulnerability was discovered within Uber’s API that allowed attackers to manipulate object properties. Attackers could escalate their privileges through mass assignment, gaining access to user account data, and even performing administrative actions such as changing payment methods and trip history.
Impact:
- The attackers exploited the vulnerability to change user payment details and access confidential trip data.
- Financial fraud: Attackers potentially used the compromised data for fraudulent activities, costing Uber financially.
- Damage to brand reputation: The breach led to increased public scrutiny over Uber’s security practices.
Lessons Learned:
- The incident illustrates the risks of mass assignment vulnerabilities combined with improper authorisation controls. Attackers manipulated API request payloads to change fields they should not have been able to access, thereby escalating their privileges.
6. Instagram API Privacy Exposure (2018)
Although this breach took place a few years ago, the Instagram API incident serves as a prime example of broken object property level authorisation. Attackers were able to exploit flaws in Instagram’s API to gain access to users’ private photos and videos, which should have been protected by strict object-level authorisation. Due to excessive data exposure, attackers could view sensitive media that was meant to be private.
Impact:
- Millions of private user photos were exposed to malicious actors.
- Instagram was forced to issue an apology and enhance their API security practices.
- Regulatory scrutiny: Instagram faced legal challenges over privacy violations, especially considering the GDPR framework.
Lessons Learned:
- Instagram’s failure to properly validate object properties meant that unauthorised users could access more information than they should have. This highlights the importance of not assuming that only authorised properties are being accessed by clients.
7. LinkedIn Data Leak (2021)
In a widely publicised incident, hackers scraped publicly available information from LinkedIn by exploiting an API vulnerability. While this was not a direct case of Broken Object Property Level Authorisation, it illustrates the broader category of excessive data exposure. Attackers were able to gather an extraordinary amount of data, including details about users’ work history, education, and even their connections, which were not intended to be available in such a raw format.
Impact:
- 700 million user profiles were scraped, leading to a vast leak of personal data.
- Privacy violations: Sensitive data, including phone numbers and work history, was exposed.
- Reputational damage: LinkedIn’s reputation was tarnished as users became concerned about how their data was being handled.
Lessons Learned:
- The lack of object-level authorisation led to a large-scale data leak. This breach was a result of an API that returned more information than necessary, demonstrating how excessive data exposure can lead to serious issues.
8. Capital One API Breach (2019)
In one of the most high-profile data breaches, Capital One suffered a massive API hack in 2019. The breach was caused by a misconfigured Web Application Firewall (WAF), but the exploitation of object property-level authorisation was also a contributing factor. The attacker was able to access more than 100 million customer accounts by querying an exposed API endpoint. Some sensitive fields, such as customer credit scores and social security numbers, were not protected by appropriate authorisation checks.
Impact:
- Over 100 million customers were affected, with names, addresses, credit scores, and other sensitive data exposed.
- Capital One faced a $80 million fine from the U.S. Office of the Comptroller of the Currency (OCC).
- Reputational damage: Customers lost trust in the security of Capital One’s systems, leading to a significant erosion of brand equity.
Lessons Learned:
- The breach illustrates how misconfigured APIs, combined with improper object-level validation, can lead to large-scale exposure of sensitive data. Attackers were able to manipulate API requests to gain unauthorised access to sensitive properties within the data structure.
9. Snapchat API Vulnerability (2014)
This earlier example involves a vulnerability in Snapchat’s API that exposed users’ private data. Attackers exploited broken object property authorisation to access private messages, photos, and videos that should have been protected from unauthorised access. The flaw was later patched, but not before attackers were able to extract and distribute millions of user snaps.
Impact:
- The breach affected nearly 100 million users, with private data exposed.
- Snapchat had to implement additional security measures to prevent further breaches.
- The incident raised questions about the security of social media platforms and how they handle user data.
Lessons Learned:
- The vulnerability stemmed from the lack of proper object-level authorisation checks, which allowed attackers to exploit the API and access properties that should have been restricted.
Hypothetical Scenarios
1. Banking App Data Leak
A fintech company implements an API for retrieving customer account details. Due to improper property-level validation, the API returns hidden fields such as account_balance and loan_status to unauthorised users. Attackers scrape this data and sell it on underground marketplaces.
Potential Consequences:
- Loss of customer trust and revenue.
- Regulatory fines under frameworks like GDPR or PCI DSS.
2. SaaS Mass Assignment Exploit
A SaaS application enables users to update their profiles through a PATCH API. A malicious user adds a role field in the payload, escalating their privileges to “admin”:
json
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{
“email”: “[email protected]”,
“role”: “admin”
}
The API fails to validate this property, granting admin access. The attacker deletes accounts and leaks sensitive company data.
Potential Consequences:
- Service disruption.
- Legal implications and reputational damage.
3. Healthcare API Exploit
An API for a healthcare app provides patient records to authorised practitioners. Due to a lack of fine-grained authorisation, an attacker intercepts and modifies API requests to access additional patient fields, such as HIV_status and mental_health_history.
Potential Consequences:
- Privacy violations with serious ethical and legal implications.
- Class-action lawsuits.
Lessons from Incidents
1. Root Cause Analysis
Each of these incidents stems from inadequate validation mechanisms, specifically at the object property level. APIs should enforce strict validation rules, ensuring that only authorised properties are exposed or modifiable based on the user’s role.
2. Business and Legal Implications
Failing to address API security can lead to:
- Monetary Penalties: Regulatory fines under laws like GDPR, CCPA, or HIPAA.
- Reputational Harm: Public disclosure of incidents erodes customer trust.
- Operational Disruption: Exploits can lead to downtime, affecting service delivery.
Implications for Software Developers
The consequences of API3:2023 extend beyond security. For businesses, a breach caused by broken object property level authorisation can lead to:
- Data Breaches: Exposure of sensitive information damages trust and incurs regulatory fines.
- Financial Loss: Fraudulent activities arising from unauthorised data manipulation.
- Reputational Damage: Public disclosure of vulnerabilities erodes customer confidence.
Developers play a pivotal role in mitigating these risks by adopting secure coding practices and leveraging modern frameworks to enforce granular authorisation.
Mitigation Strategies for Developers
1. Implement Server-Side Authorisation Checks
Relying on client-side validation is inherently insecure. Always validate requests on the server, ensuring that object properties being accessed or modified align with the user’s role and permissions.
2. Use Allow Lists for Data Exposure
Adopt a “deny by default” approach where only explicitly allowed properties are returned in API responses. This ensures that sensitive data is never inadvertently exposed.
Example: Explicitly Specify Return Fields
Instead of:
sql
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SELECT * FROM users WHERE id = ?
Use:
sql
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SELECT name, email FROM users WHERE id = ?
3. Enforce Data Validation for Mass Assignment
Use frameworks that support strong typing and enforce strict schema validation. For instance, libraries like Joi (JavaScript) or Pydantic (Python) can validate incoming payloads against a predefined schema.
4. Adopt Role-Based Access Control (RBAC)
Implement RBAC to ensure users can only access properties relevant to their role.
Example:
A GET /user/:id endpoint should filter response data based on the user’s role:
- Admin: {id, name, email, role}
- Regular User: {id, name, email}
5. Perform Security-Focused Code Reviews
Incorporate a checklist for object property validation during code reviews to catch potential lapses early.
Practical Insights for Penetration Testers
As penetration testers, your role involves identifying and demonstrating API3:2023 vulnerabilities to developers and stakeholders.
1. Testing for Excessive Data Exposure
- Manual Inspection: Analyse API responses for overexposed data.
- Automated Tools: Use tools like Burp Suite or Postman to capture API traffic and identify sensitive fields.
2. Exploiting Mass Assignment
- Payload Injection: Craft unexpected payloads with additional properties to test the API’s resilience.
- Source Code Review: Look for frameworks that lack built-in protection against mass assignment, such as older versions of Laravel or Django.
3. Reporting Vulnerabilities
Present findings with detailed steps to reproduce, risk assessments, and remediation recommendations. Use frameworks like OWASP ASVS to standardise your assessments.
Future Trends and Challenges
1. Increasing API Complexity
With microservices and serverless architectures gaining traction, managing fine-grained authorisation at scale will become even more challenging.
2. Adoption of Zero Trust Architecture
Zero Trust principles advocate minimising implicit trust within systems, necessitating robust validation mechanisms at every layer.
3. Enhanced Penetration Testing Tools
Expect tools with better AI-driven heuristics to identify object property level vulnerabilities more effectively.
Key Takeaways
- API3:2023 highlights the critical need for fine-grained authorisation at the object property level.
- Developers must implement robust server-side validation, adopt secure frameworks, and enforce RBAC.
- Penetration testers should focus on excessive data exposure and mass assignment risks to strengthen security postures.
By prioritising API security, organisations can safeguard sensitive data, enhance user trust, and mitigate the financial and reputational impacts of breaches. Addressing API3:2023 is not just a technical necessity—it’s a business imperative.
1. Common Thread of Insufficient Authorisation Checks
All of the incidents above share a common vulnerability: inadequate object-level authorisation. Without proper validation mechanisms, APIs expose sensitive properties or allow attackers to manipulate object properties, leading to severe consequences for businesses and users alike.
2. The Importance of Granular Control
Fine-grained authorisation at the object property level is essential to preventing incidents like those above. By implementing role-based access control (RBAC) and ensuring that API responses are tailored to user roles, businesses can mitigate these risks.
3. Early Detection and Rapid Response
Many of these incidents could have been mitigated through better monitoring, threat detection, and faster incident response. Organisations should have mechanisms in place to quickly identify abnormal API traffic or unauthorised access attempts.
4. Regular Security Audits and Penetration Testing
Penetration testers must focus on testing API endpoints for excessive data exposure and mass assignment vulnerabilities. Regular security audits help identify flaws before they can be exploited by malicious actors.
Strategies to Prevent API3 Incidents
For Developers
- Enforce least privilege access and validate all object properties server-side.
- Regularly audit API responses to ensure excessive data is not being exposed.
- Adopt security-conscious frameworks that inherently prevent mass assignment vulnerabilities.
For Penetration Testers
- Actively test for excessive data exposure and mass assignment vulnerabilities during security assessments.
- Use fuzzing techniques to discover properties that can be manipulated or exploited.
- Simulate attacks with unexpected payloads to test authorisation mechanisms.
By analysing past incidents and preparing for potential scenarios, organisations can fortify their API security and mitigate the risks associated with API3:2023 vulnerabilities.
Final Thoughts: Enhancing API Security to Prevent Future Incidents
API3:2023 highlights a critical area of weakness in modern API security—broken object property level authorisation. The incidents mentioned above demonstrate the significant consequences of failing to enforce proper authorisation checks at the object property level. For organisations to protect themselves, they must adopt strong authorisation practices, implement robust security controls, and perform thorough penetration testing. Addressing this issue proactively not only enhances security but also safeguards sensitive user data, reduces financial risk, and preserves the organisation’s reputation.