Security professionals know all too well the potential risks of a successful attack against an email account, and this week's cyber attack against the UK Parliament is just the latest example. The ramifications of a compromised mailbox can range from a silent advanced persistent threat (APT), to immediately disruptive ransomware or other malware.
The email attack vector can cause several problems, even if access is not linked directly to a privileged account. For example, an attacker could potentially leverage the compromised account to forward a malicious email to a privileged account, and thus have lateral movement within the application.
Consider the potential attack vectors for email:
- Phishing attempts to exploit the user and their system via social engineering. These attacks can contain ransomware or other malware.
- Persistent Presence on a compromised account to monitor email. The attack vector can be malware or simple knowledge of the credentials themselves. This is a surveillance vector by a threat actor to monitor email traffic.
- SPAM, Hacktivism, Sabotage, Denial of Service, Blackmail, etc. can involve malicious emails sent from a compromised account, including attachments that may phish other users and contain malware or illegal content.
- Lateral Movement simply by forwarding or sending a malicious email to a group of people or distribution list -- with or without prior system exploitation. Malware can potentially access your address book to perform this function automatically.
Compromise of UK Parliament reveals weak passwords
If you consider the attack on British members of Parliament, the successful exploitation could have been devastating if it went undetected. When the attack was detected, one of the first publicly disclosed mitigations was to shut down remote email access. The assumption for this step was to stop accounts from being accessed outside of the government’s trusted computing environment (i.e., within a traditional firewalled network). As of the last report, up to 90 accounts were compromised in a brute force attack due to weak passwords. Why? Security professionals had an indication that accounts were compromised from the outside and that the attack was being conducted against remote systems. Strong credentials would have helped in this situation, but it is unknown if the brute force attack used only weak passwords or included personal passwords that were reused as well. While government email systems, including those in the UK, have been considered some of the most protected, no system is perfect (yes, even with multi-factor authentication). We know that the attack was password-based, but the source of the attack and its motivation is still a mystery. Hopefully the details are disclosed soon. If a successful attack can occur at this level, it can happen to all of us.How to mitigate the risk of a similar attack
So, how can the average company or government agency protect against a similar attack? Even if you don't have sophisticated counter cyber security solutions and an unlimited budget, you can still start with these security basics:- Enable multi-factor authentication for initial access from new or untrusted systems.
- Enforce complex passwords for every user and administrator account.
- Enforce password rotations on a periodic basis and limit password history reuse.
- For administrator accounts, consider forced rotations after use in addition to periodic password changes (even for service accounts).
- Never let executables be sent via email (very old-school but it still happens today) and disable macros within applications like Microsoft Office that can actually run scripts (i.e., code).
- Ensure email systems, client mail applications, browsers, operating systems, and third-party applications have the latest security patches.
- Restrict access to sensitive email groups; never allow everyone to email an “All” group comprised of the entire company; and limit the number of email addresses a standard user can email at one time. There is no reason an average user should have more than a few dozen people in the To: line.
