Security vulnerabilities

Severity: Critical (P1)

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Summary

The Alwaysdata system suffers from a logic flaw in verifying domain ownership and handling the domain identifier (domain_id) during mailbox modification. This flaw allows an attacker to use an internal system domain identifier (alwaysdata.net) to create unauthorized local-parts on the Alwaysdata domain itself. As a result, this behavior can be abused to create paid subscriptions without billing (Billing Bypass) and to pre-register local-parts and link them to future subscriptions, leading to control over the primary email address of the subscription.

This root flaw leads to privilege escalation and bypass of financial and email security mechanisms, posing a critical risk to the platform infrastructure as a whole.

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Vulnerability #1 – Unauthorized Paid Subscription Creation (Billing Bypass)

Description:

An attacker can modify the mailbox update request and change the domain_id value to the one belonging to the system domain alwaysdata.net. After that, they can create a subscription account using the created local-part and choose any paid plan, and the subscription will be created successfully without requesting any payment method or billing verification. This results in a complete bypass of the subscription system and obtaining paid features for free.

Steps:

1. Create a regular domain inside the account.

2. Create a mailbox on this domain.

3. Intercept the mailbox modification request using Burp Suite.

4. Change domain_id to 1 and set any local-part.

5. Send the request → a mailbox named name@alwaysdata.net appears.

6. Go to the subscription creation page.

7. Enter the same name and choose any paid plan.

8. Observe that the subscription is created without requesting payment details.

Impact:

Billing bypass, privilege escalation, and unlimited resource consumption.

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Vulnerability #2 – Mailbox Local-Part Takeover on alwaysdata.net

Description:

The same flaw allows an attacker to reserve an unlimited number of local-parts on the alwaysdata.net domain. When any legitimate user later creates a subscription using one of these local-parts as the name, the subscription is linked to the pre-registered mailbox, making the primary email address of the subscription under the attacker’s control.

Steps:

1. Perform steps 1–5 from the first vulnerability to create a mailbox on alwaysdata.net.

2. Wait for another user to create a subscription using the same name.

3. Observe that the primary email address of the subscription is linked to the mailbox owned by the attacker.

Impact:

Control over the primary subscription email, interception of sensitive messages, and unauthorized access.

POC: https://admin.alwaysdata.com/support/91794/