Inside the Red Team’s Notebook: API Penetration Testing in 2025

If 2024 was the year of the "AI boom," 2025 is shaping up to be the year of the "API breach."

In the high-stakes world of Australian cybersecurity, the narrative has shifted. According to recent data from the ACSC and major threat reports (like the CyberCX 2025 outlook), nation-state actors and financially motivated syndicates are increasingly favoring software and API vulnerabilities over traditional phishing. Why? because APIs are the "direct pipeline" to your data.

At our firm, we aren't just reading these reports; we are writing them based on what we find in the field. In our recent Q3 and Q4 penetration testing engagements across Sydney and Melbourne, we have observed a disturbing trend: while companies have locked down their front doors (web apps), their side windows (APIs) are often left wide open.

This article pulls back the curtain on what our Red Teams are finding right now. We will explore the OWASP API Security Top 10, not as a theoretical list, but as a collection of real-world exploits we have successfully executed against Australian enterprises this year.

The "Shadow" Threat: Why APIs are the 2025 Battleground

Modern applications are no longer monolithic; they are collections of microservices talking to each other. This architecture is efficient for developers but a goldmine for attackers.

When we perform penetration testing services for a new client, we often discover 30-40% more API endpoints than the internal team knew existed. These "Shadow APIs" or "Zombie APIs" (deprecated versions still running) are often unmonitored and unpatched.

The 2025 Reality Check:

AI-Driven Attacks: Attackers are now using Large Language Models (LLMs) to automatically parse your API documentation (Swagger/OpenAPI) and generate custom attack scripts in seconds.
MFA is Not a Silver Bullet: Recent stats indicate that nearly 75% of advanced compromises now involve some form of MFA bypass or session hijacking—attacks that frequently target the API layer directly, skipping the UI entirely.

Field Notes: Exploiting the OWASP API Top 10

The OWASP API Security Top 10 (2023) remains the industry standard for classifying these risks. However, reading a definition is different from seeing an exploit in action.

Here is how our penetration testers are currently exploiting these vulnerabilities in real Australian environments:

1. API1:2023 - Broken Object Level Authorization (BOLA)

The "Crown Jewel" of API Vulnerabilities. BOLA remains the number one threat for a reason. It occurs when an API doesn't check if the user requesting the data is the actual owner of the data.

From the Red Team Notebook:
"During a recent mobile application penetration testing service for a Fintech client, we intercepted a traffic request used to fetch transaction history. The call looked like this: GET /api/v1/transactions?account_id=1005. By simply changing 1005 to 1006 in a repeater tool, the API returned the full transaction history of a completely different user. No error, no alert. We could have scraped the entire customer database in under an hour."

2. API3:2023 - Broken Object Property Level Authorization (BOPLA)

Formerly known as "Mass Assignment," this is a favorite among our testers because it often leads to instant administrative access.

From the Red Team Notebook:
"We were testing a user profile update function for a SaaS provider. The frontend only allowed users to update their 'Email' and 'Avatar'. However, by inspecting the JSON request, we saw the backend object model. We manually added a new parameter to the request body: "role": "ADMIN". The API blindly trusted the input and updated the user object in the database. Our standard user account was instantly promoted to a Super Admin."

3. API6:2023 - Unrestricted Access to Sensitive Business Flows

This is a logic flaw, not a coding bug. It happens when an API exposes a business flow (like buying a ticket or resetting a password) without considering how it could be abused by automation.

From the Red Team Notebook:
"A retail client engaged us for penetration testing services after their site crashed during a launch. They suspected DDoS, but it was actually 'Scalper Bots.' We demonstrated how a simple script could call their reserve_item endpoint 500 times per second. Because the API didn't require a CAPTCHA or enforce strict rate limiting on that specific logic flow, a single attacker could lock up their entire inventory instantly."

4. API2:2023 - Broken Authentication

In 2025, "Broken Authentication" often means weak token management.

From the Red Team Notebook:
"We found an API that issued 'access tokens' with no expiry date. We managed to sniff a token from a developer's test session logged in a forgotten Splunk dashboard. That token allowed us to access the production environment as that developer indefinitely, completely bypassing their Okta SSO."

5. API8:2023 - Security Misconfiguration

This often manifests as verbose error messages or unnecessary HTTP methods left enabled.

From the Red Team Notebook:
"We sent a malformed request to an API and it crashed, returning a full 'Stack Trace' error. This error message revealed the exact version of the backend server (which had a known CVE) and the internal IP addresses of their database clusters. It was a roadmap for our next lateral movement."

Automated Scanners vs. Human Red Teams

A common question we hear is: "Can't we just buy a tool to scan for this?"

Tools are excellent for finding known vulnerabilities (like an outdated library). However, tools cannot understand business logic. A scanner doesn't know that User A shouldn't be able to see User B's data; it just sees that the request returned a "200 OK" status.

To illustrate why you need a human penetration testing provider, we’ve compiled this comparison based on our recent test results:

  
            Vulnerability Type
            Automated Scanner Detection
            Human Pen Tester / Red Team
            Real World Impact
        
            SQL Injection (Basic)
            High (95% detection)
            High (Verification only)
            Data Theft
        
            BOLA (IDOR)
            Low (< 10% detection)
            Critical (Core focus)
            Data Leakage between users
        
            Business Logic Flaws
            Zero (Cannot understand logic)
            Critical (Requires context)
            Fraud, Free Purchases, Admin Takeover
        
            Broken Access Control (Complex)
            Low
            High (Multi-step attacks)
            Privilege Escalation
        
            Race Conditions
            Very Low
            Medium/High
            Duplicate credits, Financial fraud

The Full OWASP API Security Top 10 (2023) Reference

For your compliance teams (PCI-DSS, ISO 27001, APRA CPS 234), here is the complete list of risks that our penetration testing service covers:

API1:2023 Broken Object Level Authorization (BOLA)
API2:2023 Broken Authentication
API3:2023 Broken Object Property Level Authorization
API4:2023 Unrestricted Resource Consumption
API5:2023 Broken Function Level Authorization
API6:2023 Unrestricted Access to Sensitive Business Flows
API7:2023 Server Side Request Forgery (SSRF)
API8:2023 Security Misconfiguration
API9:2023 Improper Inventory Management
API10:2023 Unsafe Consumption of APIs (Trusting third-party data too much)

The Cost of "Penetration Testing as a Service" (PTaaS)

In 2025, the pricing model for penetration testing cost is evolving. Traditional "point-in-time" testing (once a year) is often insufficient for agile teams deploying code weekly.

We are seeing a shift toward Penetration Testing as a Service (PTaaS). This model provides:

Continuous scanning of endpoints.
On-demand manual re-testing when code changes.
Real-time vulnerability dashboards.

Cost Estimation for Australia (2025 Market Rates):

Basic API Assessment (Up to 10 endpoints): $4,500 - $7,000 AUD.
Comprehensive App & API Test (Complex Logic): $12,000 - $20,000+ AUD.
Red Teaming (Full adversarial simulation): Custom quoting required based on scope (Physical + Digital).

Note: Beware of cheap "quote generators" that offer a "penetration test" for $1,000. These are almost invariably just automated scans repackaged as a report. They will not satisfy auditors or protect you from skilled attackers.

The attackers targeting Australian businesses in 2025 are sophisticated, patient, and often automated. They are actively looking for the API endpoints you forgot to secure.

Securing your API layer is no longer an optional "extra"—it is the most critical component of your cyber security posture. Whether you need a one-off validation for a new product launch or a continuous penetration testing provider, the goal is the same: find the flaws before they do.

Ready to test your defenses against real-world attack vectors? Contact our Offensive Security Team today for a scoping call. Let’s verify your security controls with the same rigour legitimate adversaries will use against you.