In this blog, we will discuss what security risks can third-party APIs create, how can a cert-in empanelled auditor test third-party API security, what data should be checked when an application uses third-party APIs, how does a cert-in empanelled auditor assess API authentication, how can unsafe Third-Party API responses create security issues and why choose a CERT-In empanelled auditor for Third-Party API assessment.
What Security Risks Can Third-Party APIs Create?
Third-party APIs connect your application with external services, but they can also introduce security risks. If external data, requests, or responses are not handled correctly, attackers may find ways to access information or misuse application functions.
1. Unsafe Consumption of External API Data
An application may accept data from a third-party API without checking whether it is valid or expected. If that data is processed without proper validation, it may affect application functions or create security weaknesses.
2. Weak Authentication Between Systems
Third-party APIs often use API keys, access tokens, or other credentials. Weak credentials, poor token handling, or improper authentication checks can allow unauthorized systems or users to access the API.
3. Missing Authorization Checks
Authentication confirms who is making a request, but authorization decides what they can access. Missing authorization checks may allow users to access another user’s data or functions that should be restricted.
4. Excessive Data Exposure
An API may return more information than the application actually needs. This could include customer details, internal identifiers, account information, or other sensitive fields.
5. Insecure API Responses
Applications may trust responses received from external services without checking their content. Incorrect handling of these responses can affect transactions, account actions, or other application processes.
6. Unvalidated Redirects and External Requests
An application may redirect users or make requests based on external input. If these destinations are not properly checked, attackers may use them to send users or systems to unauthorized locations.
7. Resource Consumption Through External Services
A third-party API can also affect application resources. Poor controls around API requests, timeouts, or response sizes may cause excessive resource usage and service availability problems.
How Can a CERT-In Empanelled Auditor Test Third-Party API Security?
A CERT-In empanelled auditor can assess the security controls around third-party APIs as part of an agreed audit or VAPT scope. The testing focuses on how the application communicates with external services and protects the data exchanged between them.
1. Mapping All Third-Party API Connections
The auditor first identifies the external APIs connected to the application. This helps establish which services exchange data with the application.
2. Identifying Data Sent to External APIs
The assessment checks what information is shared with third-party services. This can include customer details, transaction information, identifiers, and authentication data.
3. Reviewing Authentication and API Credentials
API keys, tokens, and other credentials are reviewed to check whether they are properly protected and used only for their intended purpose.
4. Testing Authorization Controls
The auditor checks whether users can access only the API functions and data allowed for their role. This may include testing different user accounts and permissions.
5. Testing API Input and Output Validation
User-controlled inputs and API responses are tested to check whether the application properly validates data received from external services.
6. Checking Error Handling
Error messages are reviewed to identify whether they expose sensitive information such as internal paths, API details, system information, or credentials.
7. Reviewing API Security Configurations
The assessment can include checks for exposed endpoints, unnecessary methods, weak security settings, outdated API versions, and other configuration issues.
What Data Should Be Checked When an Application Uses Third-Party APIs?
Third-party integrations can exchange sensitive information between multiple systems. The assessment should check what data is sent, received, stored, and exposed through these connections.
1. Customer Information
Customer names, contact details, account information, and other personal data should be reviewed to ensure that only required information is shared.
2. Payment and Transaction Data
Payment details, transaction values, order information, and transaction identifiers should be checked for unnecessary exposure or improper handling.
3. Authentication Tokens
Access tokens and session-related information should not be exposed through API responses, browser data, logs, or error messages.
4. API Keys and Secrets
API credentials must be protected from exposure through source code, responses, logs, configuration files, or error messages.
5. Personal and Business Information
Applications may share employee, customer, organization, or business information with external services. The assessment checks whether this data is properly controlled.
6. Data Returned by External APIs
Third-party responses should be reviewed to identify sensitive fields that the application receives but does not need to use.
7. Sensitive Data in Logs and Error Messages
Logs and errors should not reveal credentials, tokens, personal information, internal API details, or other sensitive application data.
How Does a CERT-In Empanelled Auditor Assess API Authentication?
API authentication testing checks whether only authorized users and systems can access the available API functions.
1. Reviewing API Keys
The auditor checks how API keys are generated, stored, transmitted, and used. Exposed or poorly protected keys can create unauthorized access risks.
2. Testing Access Tokens
Access tokens are tested to verify whether they are properly validated before API access is granted.
3. Checking Token Expiration
The assessment checks whether expired tokens are rejected and whether tokens remain valid longer than required.
4. Testing Credential Reuse
Credentials may be tested across different API functions and environments to check whether access is properly restricted.
5. Reviewing Service-to-Service Authentication
Where two systems communicate directly, the authentication mechanism between them should be checked to ensure that unauthorized systems cannot make trusted requests.
6. Checking Authentication Failures
The auditor checks how the API responds to invalid credentials, missing tokens, expired tokens, and repeated failed authentication attempts.
Can Third-Party APIs Create Payment and Financial Security Risks?
Yes. Payment integrations can introduce additional security risks because application data must be exchanged with payment gateways and other financial services.
1. Testing Payment API Requests
Payment requests are checked to determine whether important values are properly validated before they are sent to the payment service.
2. Checking Transaction Parameters
Values such as transaction amounts, currencies, order IDs, and customer identifiers should be validated on the server.
3. Testing Payment Status Responses
The application should not accept a payment as successful simply because a user-controlled value says that the transaction was completed. Payment status should be verified through trusted server-side checks.
4. Checking Refund APIs
Refund functions should be tested to ensure that users cannot modify refund amounts, transaction IDs, or other parameters without proper authorization.
5. Testing Transaction Identifiers
Transaction and order IDs should be checked to ensure that one customer cannot use another customer’s identifier to access or modify a transaction.
6. Reviewing Payment Gateway Callbacks
Callbacks and webhooks from payment services should be authenticated and validated before the application processes them.
7. Testing Duplicate Transaction Handling
The assessment should check whether the same payment request can be processed more than once or whether repeated requests can create duplicate transactions.
How Can Unsafe Third-Party API Responses Create Security Issues?
An application should not automatically trust everything returned by an external API. Responses should be checked before they are used by application functions.
1. Accepting Unvalidated External Data
External data should be validated before being processed. Unexpected values should not be allowed to affect sensitive application functions.
2. Processing Unexpected API Responses
The application should handle missing, incorrect, or unexpected response values safely without causing unauthorized actions.
3. Trusting External Status Values
Payment, verification, approval, or account status values received from an external service should be properly verified before the application takes action.
4. Following Unvalidated Redirects
Redirect URLs received through external services should be checked before users or systems are sent to them.
5. Processing Excessive Response Data
Applications should process only the data they require. Unnecessary sensitive fields should not be exposed to users or stored without a valid purpose.
6. Missing Response Timeouts
Applications should use suitable timeouts when communicating with external APIs. Without them, a slow or unavailable service can consume application resources.
What Should Be Checked in Third-Party API Configurations?
Configuration errors can expose APIs or create unnecessary access paths. These settings should be reviewed as part of the security assessment.
1. Exposed API Documentation
Publicly accessible API documentation may reveal endpoints, parameters, authentication methods, or internal functionality that should not be available to everyone.
2. Deprecated API Versions
Older API versions may have weaker security controls. Unused versions should be removed or properly protected.
3. Unused API Endpoints
Unused endpoints can increase the number of available access points. They should be removed or restricted when no longer required.
4. Weak CORS Settings
Incorrect CORS settings may allow unauthorized websites to interact with APIs through a user’s browser.
5. Insecure HTTP Methods
APIs should allow only the HTTP methods required for their functions. Unnecessary methods can create additional security risks.
6. Debug and Test Endpoints
Debug, development, and test endpoints should not remain publicly accessible in production environments.
7. Incorrect Security Configurations
Other settings, including authentication, TLS, access controls, and API gateway rules, should be reviewed to identify configurations that could expose the application or its data.
Can a CERT-In Empanelled Auditor Test the Full Third-Party API Attack Path?
1. Starting With an Authenticated Application User
Testing can begin with an authorized test account to understand what API functions and data are available to that user.
2. Identifying Third-Party API Requests
The auditor can identify API requests made between the application and external services, including the data and parameters exchanged.
3. Tracking Data Between Systems
The assessment follows how information moves between the application and third-party service to identify where sensitive data may be exposed or improperly handled.
4. Testing User-Controlled API Parameters
User-controlled values such as account IDs, transaction IDs, object IDs, and other parameters can be tested to check whether they are properly validated.
5. Testing Authorization at Each Step
Authorization controls are checked at different points to determine whether a user can access functions or information outside their permitted scope.
6. Checking the Final Data Access
The auditor verifies whether the complete attack path can result in unauthorized data access, account actions, or transaction changes.
7. Documenting the Complete Security Finding
If a vulnerability is identified, the finding should document the affected API, security impact, evidence, risk level, and recommended remediation.
Why Choose a CERT-In Empanelled Auditor for Third-Party API Assessment?
1. Verified CERT-In Empanelment
A CERT-In empanelled organisation is listed by CERT-In for information security auditing activities within its approved scope.
2. Web Application Security Audit Capability
Third-party APIs are often connected to web applications, making web application security testing an important part of the assessment.
3. API Security Assessment Experience
API testing can help identify authorization, authentication, input validation, data exposure, and business logic weaknesses.
4. Payment Gateway Security Assessment Capability
For applications handling payments, API testing can also cover transaction requests, payment responses, callbacks, refunds, and transaction identifiers.
5. Structured Security Audit Approach
A defined testing process helps ensure that the agreed API scope, security controls, findings, and evidence are properly assessed.
6. Findings Based on the Defined Audit Scope
The final assessment should clearly state what was tested, which issues were identified, and what actions are recommended based on the agreed scope.
Conclusion
Third-party APIs can create security risks when authentication, authorization, data validation, or transaction controls are not properly implemented. A CERT-In empanelled auditor like Peneto Labs can assess these connections as part of the defined audit scope and help identify weaknesses across the API attack path. Regular API security testing can help businesses find and address issues before they affect customer data or critical transactions.
Want to learn more about web application security, API risks, VAPT, and penetration testing? Keep visiting the Peneto Labs blog for simple, practical insights that can help you better understand common security risks and testing approaches. Stay tuned for more security topics and expert guidance.