> For the complete documentation index, see [llms.txt](https://cortex-docs.paloaltonetworks.com/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://cortex-docs.paloaltonetworks.com/analytics-alerts/alerts-by-name/email-attachment-with-a-potentially-malicious-file-extension.md).

# Email attachment with a potentially malicious file extension

### Synopsis

| Field                | Value                                       |
| -------------------- | ------------------------------------------- |
| Activation Period    | 14 Days                                     |
| Training Period      | 30 Days                                     |
| Test Period          | N/A (single event)                          |
| Deduplication Period | 1 Hour 30 Minutes                           |
| Required Data        | Microsoft 365 Emails                        |
| Detection Modules    | Email                                       |
| ATT\&CK Tactic       | Initial Access (TA0001), Execution (TA0002) |
| ATT\&CK Technique    | Phishing (T1566), User Execution (T1204)    |
| Severity             | Informational                               |

### Description

The email message includes attachments with file types that are typically blocked by the email vendor as a precaution due to their suspicious nature.

### Attacker's Goals

Trick users into clicking on malicious attachments

* Deploy malicious attachments through emails to compromise systems, gain unauthorized access, or facilitate cyber threats.

### Investigative actions

* Check the file types and investigate the legitimacy of files intended to be sent via email.
* Scrutinize the attachments for any suspicious indications.
* Confirm whether the attachments were successfully delivered to the recipient's mailbox.
* If the attachments were delivered successfully, verify whether the recipient downloaded them.
* Check the email address for any unusual spellings.
* Check the email address for any missing letters.
* Verify the sender's domain to confirm its legitimacy.
* Examine the sender's IP address and reputation.
* Verify whether the sender's IP address has appeared in different log sources before.
* Verify if the sender's IP address is identifiable.

### Variations

<details>

<summary>Attachment(s) with a potentially malicious file extension unusual for the organization</summary>

**Synopsis**

| Field             | Value                                       |
| ----------------- | ------------------------------------------- |
| ATT\&CK Tactic    | Initial Access (TA0001), Execution (TA0002) |
| ATT\&CK Technique | Phishing (T1566), User Execution (T1204)    |
| Severity          | Informational                               |

**Description**

At least one attachment with a potentially malicious file extension was received in an email for the first time within the organization in the past 30 days.

**Attacker's Goals**

Trick users into clicking on malicious attachments

* Deploy malicious attachments through emails to compromise systems, gain unauthorized access, or facilitate cyber threats.

**Investigative actions**

* Check the file types and investigate the legitimacy of files intended to be sent via email.
* Scrutinize the attachments for any suspicious indications.
* Confirm whether the attachments were successfully delivered to the recipient's mailbox.
* If the attachments were delivered successfully, verify whether the recipient downloaded them.
* Check the email address for any unusual spellings.
* Check the email address for any missing letters.
* Verify the sender's domain to confirm its legitimacy.
* Examine the sender's IP address and reputation.
* Verify whether the sender's IP address has appeared in different log sources before.
* Verify if the sender's IP address is identifiable.

</details>

<details>

<summary>Attachment(s) with a potentially malicious file extension unusual for the recipient</summary>

**Synopsis**

| Field             | Value                                       |
| ----------------- | ------------------------------------------- |
| ATT\&CK Tactic    | Initial Access (TA0001), Execution (TA0002) |
| ATT\&CK Technique | Phishing (T1566), User Execution (T1204)    |
| Severity          | Informational                               |

**Description**

At least one attachment with a potentially malicious file extension was received in an email for the first time for the recipient in the past 30 days.

**Attacker's Goals**

Trick users into clicking on malicious attachments

* Deploy malicious attachments through emails to compromise systems, gain unauthorized access, or facilitate cyber threats.

**Investigative actions**

* Check the file types and investigate the legitimacy of files intended to be sent via email.
* Scrutinize the attachments for any suspicious indications.
* Confirm whether the attachments were successfully delivered to the recipient's mailbox.
* If the attachments were delivered successfully, verify whether the recipient downloaded them.
* Check the email address for any unusual spellings.
* Check the email address for any missing letters.
* Verify the sender's domain to confirm its legitimacy.
* Examine the sender's IP address and reputation.
* Verify whether the sender's IP address has appeared in different log sources before.
* Verify if the sender's IP address is identifiable.

</details>


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