Mail Server Misconfiguration

Mail Server Misconfiguration

Overview of the Vulnerability

A Sender Policy Framework (SPF) and DomainKeys Identified Mail (DKIM) are security controls used by email domains to prevent spoofing. A missing or misconfigured SPF or DKIM on a domain enables an attacker to spoof the name of a domain and send emails on its behalf. The misconfiguration on this mail server allows an attacker to use a trusted domain for email spoofing, commonly used in phishing and spam campaigns to appear as if the emails originate from a legitimate source.

Business Impact

Depending on the type of misconfiguration found in the mail server, an attacker who is able to manipulate and use the domain as part of a phishing or spam campaign can cause reputational damage to the business.

Steps to Reproduce

1. Using the following command to verify the target is a domain without an MX record:

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1. Use dig or nslookup to request details for DMARC:

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1. Send a test email using the following application:

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Proof of Concept (PoC)

The screenshot(s) below demonstrates the mail server misconfiguration:

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Guidance

Provide a step-by-step walkthrough with a screenshot on how you exploited the vulnerability. Your submission must include evidence of the vulnerability and not be theoretical in nature.

Demonstrate the impact of having email spoofing on the specific domain identified. In the Steps to Reproduce section, include any additional steps needed to identify the misconfiguration you have identified.

Attempt to escalate the misconfiguration to perform additional actions. If this is possible, provide a full Proof of Concept (PoC).

Recommendation(s)

There is no single technique to stop mail server misconfigurations from occurring. However, securely implementing the SPF, DMARC and DKIM with the right combination of defensive measures can prevent and limit the impact of these mail server misconfigurations.