Executive Summary

This vulnerability exists in Plunk, an open-source email platform using AWS SES, in versions prior to 0.9.0. The /webhooks/sns endpoint accepts Amazon SNS notification payloads without verifying the SNS signature, certificate, or topic ARN. This means that anyone can send forged webhook requests that appear valid.

Because of this lack of verification, an unauthenticated attacker can spoof SNS events to trigger workflow automations, unsubscribe contacts, manipulate email delivery metrics, and potentially exhaust billing credits.

This issue was fixed in version 0.9.0 by adding proper verification of SNS requests.

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Impact Analysis

The vulnerability allows an attacker to spoof SNS events, which can have several impacts:

• Trigger unauthorized workflow automations.
• Unsubscribe contacts without permission.
• Manipulate email delivery metrics, potentially affecting reporting and decision-making.
• Exhaust billing credits by triggering excessive or fraudulent usage.

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Mitigation Strategies

To mitigate this vulnerability, upgrade Plunk to version 0.9.0 or later, where the /webhooks/sns endpoint properly verifies Amazon SNS notification payloads by checking the SNS signature, certificate, and topic ARN.

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Compliance Impact

The vulnerability allows unauthenticated attackers to spoof SNS events, which can lead to manipulation of email delivery metrics, unauthorized workflow automation triggers, and unsubscribing contacts without consent.

Such unauthorized actions could potentially result in non-compliance with regulations like GDPR and HIPAA, which require protection of personal data and user consent for communications.

Specifically, the ability to unsubscribe contacts or manipulate email workflows without proper authentication may violate user consent requirements and data integrity principles mandated by these standards.

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