Exfiltration via Email

A subject exfiltrates information using their corporate-issued mailbox, either via software or webmail. They will access the conversation at a later date to retrieve information on a different system.

A subject exfiltrates information using a mailbox they own or have access to, either via software or webmail. They will access the conversation at a later date to retrieve information on a different system.

Various methods can be used within Exchange to prevent internal emails being auto-forwarded to remote domains. This can prevent exfiltration via email auto-forwarding rules.

Google's Chrome browser stores cookies that can reveal valuable insights into user behavior, including login details, session durations, and frequently visited sites.

On Windows, this information is stored in the following location:

C:\Users\[Username]\AppData\Local\Google\Chrome\User Data\Default\Network\cookies.

This database file can be opened in software such as DB Browser For SQLite. The ‘cookies' table is of interest to understand recent activity within Chrome.

Google's Chrome browser stores the history of accessed websites and files downloaded.

On Windows, this information is stored in the following location:

C:/Users/<Username>/AppData/Local/Google/Chrome/User Data/Default/

On macOS:

/Users/<Username>/Library/Application Support/Google/Chrome/Default/

On Linux:

/home/<Username>/.config/google-chrome/Default/

Where /Default/ is referenced in the paths above, this is the default profile for Chrome, and can be replaced if a custom profile is used. In this location one database file is relevant, history.sqlite.
 

This database file can be opened in software such as DB Browser For SQLite. The ‘downloads’ and ‘urls’ tables are of immediate interest to understand recent activity within Chrome.

Google's Chrome browser stores some login data of accessed websites, that can provide the URLs and usernames used for authentication.

On Windows, this information is stored in the following location:

C:\Users\[Username]\AppData\Local\Google\Chrome\User Data\Default\Login Data.

This file is a database file and can be opened in software such as DB Browser For SQLite. The ‘logins’ and ‘stats’ tables are of immediate interest to understand saved login data.

The passwords are not visible as they are encrypted. However, the encryption key is stored locally and can be used to decrypt saved passwords. The key is stored in the file C:\Users\[Username]\AppData\Local\Google\Chrome\User Data\Local State, which can be read with any text editor, such as Notepad, and searching for the “encrypted_key” value. The tool decrypt_chrome_password.py (referenced) can decrypt the AES-encrypted passwords to plaintext.

A Data Loss Prevention (DLP) solution refers to policies, technologies, and controls that prevent the accidental and/or deliberate loss, misuse, or theft of data by members of an organization. Typically, DLP technology would take the form of a software agent installed on organization endpoints (such as laptops and servers).

Typical DLP technology will alert on the potential loss of data, or activity which might indicate the potential for data loss. A DLP technology may also provide automated responses to prevent data loss on a device.

Microsoft's Edge browser stores the history of accessed websites and files downloaded.

On Windows, this information is stored in the following location:

C:\Users\<Username>\AppData\Local\Microsoft\Edge\User Data\Default\

On macOS:

/Users/<Username>/Library/Application Support/Microsoft Edge/Default/

On Linux:

/home/<Username>/.config/microsoft-edge/Default/

Where /Default/ is referenced in the paths above, this is the default profile for Edge, and can be replaced if a custom profile is used. In this location one database file is relevant, history.sqlite.
 

This database file can be opened in software such as DB Browser For SQLite. The ‘downloads’ and ‘urls’ tables are of immediate interest to understand recent activity within Chrome.

Email gateway solutions offer the ability to trace inbound and outbound emails to an organization. This can be used to retrieve information such as emails sent or received, the subject line, content, attachments, timestamps, and recipients.

Mozilla's Firefox browser stores the history of accessed websites.

On Windows, this information is stored in the following location:

C:\Users\<Username>\AppData\Roaming\Mozilla\Firefox\Profiles\<Profile Name>\

On macOS:

/Users/<Username>/Library/Application Support/Firefox/Profiles/<Profile Name>/

On Linux:

/home/<Username>/.mozilla/firefox/<Profile Name>/

In this location two database files are relevant, places.sqlite (browser history and bookmarks) and favicons.sqlite (favicons for visited websites and bookmarks).
 

These database files can be opened in software such as DB Browser For SQLite.

The following detection is a default alert policy that should be enabled in all tenants automatically.

To view this alert policy, access the Microsoft Defender portal at https://security.microsoft.com, go to Email & collaboration > Policies & rules > Alert policy. Or, to go directly to the Alert policy page, use https://security.microsoft.com/alertpoliciesv2.

This rule will generate an alert when a forwarding/redirect rule is created within Exchange or OWA.

This detection monitors the granting of mailbox read permissions, an operation that enables a user account to access another user's or shared mailbox. By alerting on this permission change in Microsoft Defender, investigators gain early visibility into potential misuse of mailbox data and can trace both the granting account and the recipient of the access.

In the Microsoft Defender portal at https://security.microsoft.com, navigate to Email & collaboration > Policies & rules > Alert policy. To go directly to the Alert policy page, use https://security.microsoft.com/alertpoliciesv2.

Click |+ New Alert Policy" in the top-left corner. Assign a clear name to the alert policy and select an appropriate Severity and Category. On the next page, under “Activity is”, search for and select Granted mailbox permission. Configure the remaining settings as required. If the intention is only to alert on these events generated by specific accounts, this can be achieved by adding a condition with either User: User is or User: User tags are.

When reviewing an alert generated by this rule, select an activity row in the Activity list table to display related information. A panel will open on the right-hand side of the alert page, under “Activity details”, showing the Item (target mailbox friendly name), User (email address of the account that made the change), IP address, and timestamp. To identify the account that was granted read access to the mailbox, review the Parameters JSON output and retrieve the “Value” (object ID) located next to "User": "Name". This ID can then be searched in the “All users” section of Entra ID to identify the target user account.

Message trace is a feature within Exchange that permits the ability to identify inbound and outbound emails within the organization.

This can be used to see which mailboxes have sent or received emails, the time, the subject line, and recipients.