Ep. 1 – Breaking OTP Security, Exploiting Static Domains & Privilege Escalation via Role Misconfigurations

What if your OTP security wasn’t secure at all? What if a static domain—something most people ignore—could lead to full account takeover? And what if flawed role management allowed admins to escalate privileges?

In this episode of Hacked & Secured: Pentest Exploits & Mitigations, we break down three real-world security failures that turned minor oversights into critical exploits:

• Leaking OTPs in API responses – Breaking authentication at the source.
• Static domain to account takeover – When persistence turns into a full exploit.
• Privilege escalation via role mismanagement – How attackers bypass access controls.

Learn how these vulnerabilities were discovered, exploited, and mitigated.

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Chapters

• 0:10 INTRO
• 1:00 FINDING #1 - The Vulnerability That Defeats OTP Security: Leaking OTP Codes in API Responses
• 5:20 FINDING #2 - From Static Domain to Account Takeover: The Power of Persistence
• 12:05 FINDING #3 - Privilege Escalation via User Invitations and Role Assignment
• 16:49 OUTRO

Transcript

INTRO

What if your OTP security wasn’t secure at all because the app itself leaked the code?
What if a static domain—something most people ignore—could lead to full account takeover?
And what if a flawed role management system let an attacker escalate privileges and take over an entire organisation?

Today, we’re breaking down three real-world security failures—each proving that simple oversights can lead to critical exploits.
I’m Amin Malekpour, and you are listening to Hacked & Secured: Pentest Exploits & Mitigations.

FINDING #1 - The Vulnerability That Defeats OTP Security: Leaking OTP Codes in API Responses

Alright, let’s dive into the first vulnerability reported by Tinopreter on the HackerOne bug bounty platform. This issue involves a serious flaw in the implementation of OTP systems—one of those findings that makes you wonder, “If OTPs aren’t implemented correctly, are they even worth the trouble?"

Let us break it down, see what went wrong, and figure out what lessons we can take away from this finding!

First things first—what is an OTP? It’s a One-Time Password sent to users to verify their identity. It’s meant to add an extra layer of security, right? But here is the twist—what if the OTP itself gets leaked in the API response?

Well, that is exactly what happened in this case. The application asked users for their phone number, sent the OTP to their phone, and included the OTP in the server’s response to the client.

This completely defeated the purpose of having an OTP. Why? Because anyone who intercepted that response could use the leaked OTP to hijack accounts or even create junk accounts with ease. It’s not just a technical flaw—it’s a breach of trust for every user on the platform.

For Tinopreter, here’s how this issue unfolded across two different applications:

• First App:
  Users authenticate using their phone number. Once the number is entered, the server sends an OTP to the phone—but it also includes the OTP in the API response. Using a tool like Burp Suite, an attacker could intercept the response, grab the OTP, and log into any account. All they needed was a valid phone number.
• Second App:
  Designed for device insurance, when requesting a quote, the server sent an OTP to validate the action and returned the OTP in the server response. This let attackers bypass validation completely and access any user’s quote, including sensitive PII data, just by entering their phone number.

In both cases, the core issue was the same: the server blindly trusted the client and disclosed sensitive authentication data. A server should never return sensitive data like OTPs in its responses. Doing so not only undermines authentication security but also puts users at serious risk of account compromise and data breaches.

What Lessons Can Be Learned Here?

For Developers:
• Never trust the client. Always assume that attackers will intercept and manipulate traffic—even if the API is meant for legitimate users.
• Always follow the principle of least privilege. Only send the bare minimum data to the client; anything beyond what is necessary increases risk.

For Pentesters:
• Always check API responses. Sensitive data like OTPs, tokens, or credentials might be hiding in plain sight. Inspect every request and response carefully.

Whether you are a pentester or a developer, the big takeaway is this: security features are only as strong as their implementation. It is not enough to just have OTP authentication—it has to be implemented right.

So, the next time you are testing an application, ask yourself:

• Is the server exposing sensitive data unnecessarily?
• Can this exposed data be used to bypass security mechanisms?

Thinking this way is how you uncover issues like this and help make applications safer for everyone.

Now, let’s move on to our next story, where we explore how creativity and persistence turned a seemingly static domain into a full-blown account takeover.

FINDING #2 - From Static Domain to Account Takeover: The Power of Persistence

This next finding comes from Bugcrowd, uncovered and detailed by r29k on his blog, r29k.com. The impact is high—and for a good reason. This story is a masterclass in turning what seems like a dead end into an incredible exploit. If you have ever been tempted to dismiss a boring-looking static domain, this one will make you think twice!

The vulnerability started with a static domain that seemed harmless at first glance—a simple landing page with a picture, a logo, and a disabled HTML form. Nothing suspicious, right? But this seemingly innocent page ended up leading to an account takeover.

Static domains are often dismissed as unimportant, but this story shows why they deserve a closer look. Sometimes, even the simplest pages hide critical vulnerabilities. In this case, the flaw allowed an attacker to hijack any user’s account with nothing more than their email address. This wasn’t some rare edge case—it highlighted real-world risk for platforms relying on similar insecure designs. It’s a powerful reminder that even the most “static” domains can pose serious threats.

Here’s how r29k uncovered this vulnerability, step by step:

1. The domain looked completely static—just a simple page with a logo, a picture, and a disabled HTML form. No directories, no hidden files, and no leads from Google or Wayback Machine. Most people would have moved on. But not r29k.
2. The form had three fields: Name, Country, and Email. Curious r29k added these as parameters in the URL, assigning the value "test" to each of them. To his surprise, the form populated and enabled a Submit button. Clicking it triggered an error: Invalid Country Code.
3. He guessed that the error came from the form expecting a country code (like US) instead of a full country name. By trying valid country codes, he bypassed the first error, only to hit another: Invalid Email Address. At this point, r29k turned to Burp Suite to see what was happening behind the scenes.
4. He realized that the form sent requests to endpoints like /countryValidate and /emailValidate. While inspecting the response from the email validation endpoint, he found two key parameters: "is_valid": false and "reason": "domain". By intercepting the server response, modifying "is_valid" from false to true, and removing the "reason" parameter, he successfully bypassed the email validation step. This highlights the importance of checking server responses thoroughly—sometimes, the server itself gives away the keys!
5. After bypassing email validation, a /register endpoint returned a response indicating that an activation link had been sent to the email address. But here’s the catch: the server included the activation link directly in the API response. Opening the link in a browser granted immediate access to the account, with no email verification required.
6. Curious r29k went a step further and tested the process with an already-registered email. Shockingly, the server still returned the activation token, even if the account was active. This meant an attacker could log into any account just by knowing the victim’s email address and grabbing the exposed token from the API response.

This was more than just a collection of clever tricks—it was a critical failure in server-side validation and secure design. By thoroughly inspecting responses and using tools like Burp Suite, r29k turned a seemingly static domain into a goldmine of vulnerabilities.

What Lessons Can Be Learned Here?

For Developers:
• Never expose sensitive data in API responses.
• Assume all client input is untrusted. Treat anything coming from the client as potentially malicious and perform all critical validations and checks on the server side.
• Always follow the principle of least privilege. Only send the minimum necessary data to the client. Remember, what isn’t exposed can’t be exploited.

For Pentesters:
• Don’t give up on “boring” domains. Just because a domain seems static doesn’t mean it’s secure. Dig deeper, experiment, and test thoroughly—you might uncover critical flaws in the most unexpected places.
• Always inspect API responses. Sensitive data exposure is a major red flag. Carefully analyze every response for tokens, links, or other valuable information that could point to potential vulnerabilities.

Here’s the big takeaway: persistence pays off. What initially seemed like a dull static domain turned into a critical flaw because r29k explored further and tested every element systematically.

Whether you’re a pentester or a developer, stay curious and always ask yourself, “What else could go wrong?” Small actions and thorough checks can make a massive difference, whether you’re building or testing an application.

Now, let’s move on to our final finding, where we explore how flawed role management led to privilege escalation.

FINDING #3 - Privilege Escalation via User Invitations and Role Assignment

To wrap up this episode, let’s dive into one last finding, reported by antonin36330 on the Hunter bug bounty platform. This privilege escalation flaw highlights how poorly implemented role and invitation systems can lead to serious security risks. It is a perfect way to conclude this episode, emphasizing the importance of strong access control and thoughtful system design.

Before we get into the exploit, let me set the stage. In the application, users had different roles with owners holding the highest privileges. Owners could access sensitive billing information and settings, while admins were restricted from viewing or modifying any billing resources. This separation was meant to safeguard financial data, but a flaw in the system allowed admins to bypass these restrictions and gain owner-level privileges.

Here’s the core issue: the system allowed admins to invite users with roles higher than their own or even assign the owner role to newly invited members. This violated the principle of least privilege and created a loophole for admins to bypass restrictions on billing access.

Here’s how the exploit worked step by step:

• The malicious admin starts by creating a fake account with minimal privileges, like a regular member. This helps them fly under the radar while setting up the attack.
• The admin then uses their privileges to invite the fake account into the application and assigns it a role. But here’s the problem: the system doesn’t validate whether the inviter—in this case, the malicious admin—has the authority to assign roles higher than their own.
• The admin can assign the owner role to the fake account, giving it unrestricted access including billing permissions.
• Once the fake account is upgraded to owner, the admin logs into it and gains full access to billing resources. They now have control over sensitive financial data and settings despite being an admin with no direct permissions to billing.

This isn’t just a technical oversight; it’s a serious breach of security best practices. With owner-level access, the malicious admin could misuse billing data, make unauthorized changes, or disrupt the organization’s financial operations.

What Lessons Can Be Learned, and What Are the Key Takeaways for Us?

For Developers:
• Enforce strict role boundaries. Never allow users to assign roles higher than their own. Validate all role changes server-side to ensure only authorized actions are permitted.
• Treat role management as a critical security layer. It’s not just a backend feature. Design systems with clear boundaries and validate every action thoroughly to prevent abuse or misuse.

For Pentesters:
• Test invitation systems for role validation flaws. Always check if users can assign roles higher than their own or improperly grant sensitive permissions like "Owner." These are red flags for potential privilege escalation.
• Investigate privilege escalation pathways. Look for opportunities to combine small oversights—like role assignments or inviting fake accounts—into larger security risks. Thinking in chains can uncover hidden vulnerabilities that would otherwise go unnoticed.

This finding highlights the importance of testing beyond traditional vulnerabilities like XSS or IDOR and digging into business logic flaws. When evaluating an application, always ask yourself:

• Can users assign roles or permissions they shouldn’t have access to?
• Are there weaknesses in how invitations or role management are handled?
• Could these flaws be combined to escalate privileges or gain unauthorized access?

Probing these areas with a critical eye can reveal significant risks that are often missed in standard testing. It’s a reminder to think critically, test thoroughly, and always consider the bigger picture when assessing an application’s security.

OUTRO

Before we wrap up, let’s highlight the importance of responsible disclosure.

As ethical hackers, the vulnerabilities we uncover come with a responsibility to make the internet safer, protect user data, and help organizations build trust. This happens when we report issues responsibly, giving organizations the chance to fix them before they’re exploited. This is the impact we should all aim for—not just finding bugs, but helping to fix them and leave the digital world better than we found it.

Now, let’s talk about you.

Have you uncovered a creative or impactful vulnerability? We’d love to hear your story! Imagine your findings inspiring thousands of professionals and helping others learn from your work. Submit your findings using the Google Form linked in the episode description. If we feature your submission, we’ll make sure to give you full credit and showcase your work to our growing community of pentesters.

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Today, we uncovered some fascinating vulnerabilities:

• Leaking OTPs in API responses that completely broke authentication.
• Digging into a static domain and turning it into an account takeover.
• Privilege escalation through flawed role management, allowing admins to gain owner-level access.

Each finding showcased the power of persistence, creativity, and understanding how vulnerabilities can be exploited while focusing on securing systems against them.

We’ll see you in the next episode—share your findings with us, stay curious, hack responsibly, and always push the boundaries!