Adversaries may target user email on local systems to collect sensitive information. Files containing email data can be acquired from a user’s local system, such as Outlook storage or cache files.
Outlook stores data locally in offline data files with an extension of .ost. Outlook 2010 and later supports .ost file sizes up to 50GB, while earlier versions of Outlook support up to 20GB.(Citation: Outlook File Sizes) IMAP accounts in Outlook 2013 (and earlier) and POP accounts use Outlook Data Files (.pst) as opposed to .ost, whereas IMAP accounts in Outlook 2016 (and later) use .ost files. Both types of Outlook data files are typically stored in C:\Users\<username>\Documents\Outlook Files or C:\Users\<username>\AppData\Local\Microsoft\Outlook.(Citation: Microsoft Outlook Files)
Detect Local Email Collection via Outlook Data File Access and Command Line Tooling
Out-of-Band Communications Channel: Establish secure out-of-band communication channels to ensure the continuity of critical communications during security incidents, data integrity attacks, or in-network communication failures. Out-of-band communication refers to using an alternative, separate communication path that is not dependent on the potentially compromised primary network infrastructure. This method can include secure messaging apps, encrypted phone lines, satellite communications, or dedicated emergency communication systems. Leveraging these alternative channels reduces the risk of adversaries intercepting, disrupting, or tampering with sensitive communications and helps coordinate an effective incident response.(Citation: TrustedSec OOB Communications)(Citation: NIST Special Publication 800-53 Revision 5)
Encrypt Sensitive Information: Protect sensitive information at rest, in transit, and during processing by using strong encryption algorithms. Encryption ensures the confidentiality and integrity of data, preventing unauthorized access or tampering. This mitigation can be implemented through the following measures:
Encrypt Data at Rest:
Encrypt Data in Transit:
Encrypt Backups:
Encrypt Application Secrets:
Database Encryption: