# Logic Flaw in Collaboration Invite Flow Allows Cross‑Organization Access

Hello folks, it’s Mr-Dix from the **BountyOrDie** squad, Back again with another logic flaw that looks small at first, but ends up breaking an important security rule behind the scenes.

Today’s story revolves around something every SaaS platform relies on heavily: **collaboration invites and organizational boundaries**.

At first, everything looked locked down properly. Turns out — it was mostly just frontend confidence.

***

### Collaboration Invites — How It’s Supposed to Work

 **The platform** allows organizations to invite collaborators via email.

**Everything seems normal at first:**

* Each email should belong to **one account**
* An email already associated with **Org B** should **not** be able to accept an invite into **Org A**
* The backend enforces this rule by rejecting duplicate email usage

When this happens, the system responds with a clean and clear error:

```http
HTTP/2 409 Conflict
```

```json
{
  "code": 7001,
  "message": "E-mail is used by another account."
}
```

So far? Looks solid. But as we all know… *what happens when the frontend is trusted a little too much?*

<figure><img src="/files/ouH60nyXdCXu6L83JwBN" alt=""><figcaption></figcaption></figure>

***

### The Breaking Point (Let’s Test the Logic)

#### Setup

* Two organizations exist:
  * **Org A** (victim org)
  * **Org B** (attacker-controlled org)
* The same email address (`email@example.com`) already has an account under **Org B**
* **Org A** sends a collaboration invite to that same email

The invited user opens the invite link.

> **At this stage, the request is rejected with a `409 Conflict` response.**

Frontend blocks the flow. Invite rejected. End of story, right?

Not quite.

***

### Let’s Break It 😈

Instead of accepting the frontend’s judgment, I intercepted the invite acceptance response using **Burp**.

<figure><img src="/files/kqPsn56RxluBbUF8Isk2" alt=""><figcaption></figcaption></figure>

Then I did something very simple:

* Changed the server response from:

  ```http
  409 Conflict
  ```
* To:

  ```http
  200 OK
  ```

With the following response body:

```json
{
  "show_onboarding": true
}
```

Forwarded the modified response back to the browser.

<figure><img src="/files/wPrHFXa4QJNGo69Wh6GF" alt=""><figcaption></figcaption></figure>

***

### What Happened Next?

No errors. No warnings. No second validation.

The invite flow completed successfully.

✅ The email already tied to **Org B.**

✅ Was now added as a collaborator to **Org A.**

✅ Despite the backend *explicitly* saying this should not be allowed.

The system fully trusted the client-side response state and moved on.

<figure><img src="/files/dDhUSeco4bpCWRw32NQO" alt=""><figcaption></figcaption></figure>

***

### Related Issue: Users Can Join Without Proper Identity Details

<figure><img src="/files/zSLzZ5qkO1v6g7i1u9pd" alt=""><figcaption></figcaption></figure>

During the onboarding step, the application requires a **Name** field.

Except… it doesn’t.

By sending:

```json
{ "name": "" }
```

Directly to the API, the request is accepted.

Result:

* A collaborator is added.
* With **no visible name.**
* This makes logs harder to read and makes it difficult to track who did what.

Quiet. Clean. Invisible.

<figure><img src="/files/HUIBZPxYqaFqJAIFf2Ly" alt=""><figcaption></figcaption></figure>

***

#### Why This Actually Matters?

This stops being about an invite very quickly. An email that should be tied to a single organization can be reused to quietly enter another one. Once inside, the user looks legitimate, operates under default roles, and blends in like they belong there.

With no strong identity enforcement during onboarding, the access becomes even harder to notice — turning a simple logic flaw into a silent way to cross organizational boundaries.

***

#### Real‑World Impact:

In simple terms, this creates a quiet way for the wrong person to get in.

Someone with bad intentions — or even a careless insider — could join organizations they don’t belong to, move between them without being noticed, and access data as if they were a trusted user.

For platforms dealing with billing, analytics, or financial information, this isn’t just a small bug. It’s a breakdown of trust between the system and its users.

***

### Final Thoughts

Frontend checks are not security. Error messages are not enforcement. And org boundaries should never be optional.

That’s the story for today. Hope you found this write‑up useful

<figure><img src="/files/mH4PoJ9fgtXd55wL0cpU" alt=""><figcaption></figcaption></figure>

<br>


---

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