🙏 Jay Shree Ram 🚩
My Other Write up:-
recap:-
In part 1, we mastered the tools (cURL & Postman).
In Part 2, we analyzed the logic-based flaws of the OWASP API Top 10.
Now, in Part 3, we tackle the technical heavyweights—the vulnerabilities that exploit how APIs process data, handle resources, and interact with internal networks.
1. Server-Side Request Forgery (SSRF) 🛰️
SSRF is one of the most dangerous vulnerabilities in cloud-native environments. It occurs when an API fetches a remote resource based on user-supplied input without proper validation.
- The Technical Mechanism: An attacker provides a URL to an internal service (like metadata services) that the API server can reach, but the attacker cannot.
- Real-World Scenario: An API has a feature to "Upload profile picture from URL." An attacker provides the URL: http://169.254.169.254/latest/meta-data/iam/security-credentials/.
- The Impact: The server fetches its own cloud credentials and returns them to the attacker, leading to a full cloud account takeover.
- Remediation: Implement strict Allow-lists for domains and protocols, and block all requests to internal IP ranges.
2. Unrestricted Resource Consumption (DoS) 📉
APIs are often built to be fast, but if they don't limit the "appetite" of a request, they can be starved of resources.
- The Technical Mechanism: Exploiting endpoints that allow users to define page sizes, upload large files, or trigger heavy computations.
- Example: An API allows fetching users with a limit parameter: /api/v1/users?limit=10. An attacker changes this to ?limit=1000000.
- The Impact: The database struggles to fetch a million records, memory spikes, and the API crashes for all legitimate users.
- Remediation: Set hard limits on all input parameters, enforce maximum file sizes, and implement global Rate Limiting.
3. Unsafe Consumption of APIs 🔗
In a microservices world, APIs talk to other APIs. This vulnerability arises when your API trusts the data coming from a third-party service too much.
- The Technical Mechanism: An attacker compromises a third-party service your API relies on, then sends malicious payloads through that "trusted" channel.
- Example: Your API integrates with a "Weather API." If the Weather API is compromised and sends a malicious script instead of a temperature, and your API displays it without sanitizing, you have a downstream XSS.
- Remediation: Treat all data as untrusted, even if it comes from a "partner" API. Apply full validation and sanitization at every entry point.
4. Advanced Injection: NoSQL & GraphQL 💉
While SQL Injection is well-known, modern APIs often use NoSQL (MongoDB) or GraphQL, which have their own unique injection patterns.
- NoSQL Injection: Using operators like {$gt: ""} to bypass authentication.
- GraphQL Introspection: If not disabled, an attacker can query __schema to see every available query and mutation in your API, essentially downloading your entire API documentation.
- Remediation: Disable GraphQL Introspection in production and use library-specific sanitization for NoSQL queries.
5. Unrestricted Access to Sensitive Business Flows 💳
Some vulnerabilities aren't about "hacking" code; they are about "gaming" the system.
- The Technical Mechanism: Exploiting the sequence of an API's business process.
- Example: A "Refer-a-Friend" API gives $10 for every referral. An attacker automates the creation of 5,000 accounts using a script to call the registration API, draining the company's marketing budget in minutes.
- Remediation: Identify high-risk business flows and add extra layers of protection like CAPTCHAs, MFA, or behavior-based anomaly detection.
Summary of Part 3
Modern API security requires a Zero-Trust approach. Whether it's data from a user, a URL, or another service, every byte must be scrutinized.
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