The global reach and considerable impact of the WannaCrypt (WannaCry/Wcry) ransomware is a wake-up call for organisations and governments around the world. This ongoing cyberthreat will continue to adapt to take advantage of weaknesses in IT systems and procedures. New variants of this malware may cause even more damage if you do not act immediately.
At Mimecast our first priority is to help protect our customers against the latest threats. Our services help protect email, which has traditionally been the primary attack route for ransomware.
Early samples have revealed that the ransomware is spread over local networks and the Internet by abusing Server Message Block (SMB) protocol weaknesses. Although no Wcry ‘smoking gun’ infection emails have yet been found, it is highly likely that future variants will use email.
This short guide is designed to help all organisations complete a review of network security, backup and business continuity systems and processes.
We are also providing additional insights into how to make easy and quick configuration changes to ensure your Targeted Threat Protection solution is optimised. As many of you already know, a comprehensive ‘defence in depth’ strategy is the best approach to mitigation of current and future variants of Wcry and other ransomware.
Patching
Every organisation must ensure its IT systems are regularly updated. Microsoft security updates are released on the second Tuesday of each month (Patch Tuesday).
Microsoft released a security update back in March which addresses the vulnerability that Wcry is exploiting. For those organisations who have not yet applied the security update, you should immediately deploy Microsoft Security Bulletin MS17-010.
If you are using a legacy, now unsupported version of Windows, you should consider upgrading immediately. However, if this is impossible in the short term, Microsoft has taken the unusual measure of releasing a security patch that can buy you time to upgrade.
Microsoft has provided its own detailed guidance to defend against Wcry here.
Network hardening
Good security practice dictates removing or disabling unnecessary services to reduce the potential attack surface.
WannaCry has spread quickly by abusing vulnerabilities in Server Message Block network protocol. Unless you have a very good reason not to, disable the SMBv1 protocol on your network, while also ensuring SMB cannot be directly accessed from the Internet.
Disable or block other legacy protocols on your network that you are not using.
Email security: Mimecast’s Ransomware Defense
For customers of Mimecast Targeted Threat Protection, we advise a number of activities:
URL protect – configure a policy in line with our best practice guide in Mimecaster Central. Ensure a policy is applied to all users. Rewriting all URLs to scan for unsafe content at time-of-click is the best approach to preventing inbound URL-based phishing.
Attachment protect – configure the ‘Safe Files’ option for all users to ensure inbound Microsoft Office files are converted to a safe and benign format. For users who require editable documents, ensure Attachment Protect’s sandboxing is configured. Refer to the best practice guide in Mimecaster Central for details.
Internal email protect – this service provides protection for URLs and attachments in both outbound email and also mails sent internally. Ensure policies are applied to all users and ensure remediation capabilities are enabled. Refer to our best practice guide for configuration recommendations.
Mimecast customers using Mimecast’s secure email gateway, we advise using the most up to date attachment management definition as there are reports of executable files masquerading as Excel files with an administrator hold on dangerous files types. This, in conjunction with the Suspected Malware policy with the ability to hold Office files containing macros, provides another layer of detection, but does not provide the analysis provided by Attachment Protect.
Mimecast’s ARMed SMTP (Advanced Reputation Management) combines malware, reputation and anti-spam checks to reject unwanted email.
Since a very high percentage of ransomware is spread by email attachments, we urge organisations to consider using sandboxing and/or safe file conversion services.
DNS authentication capabilities such as DKIM and SPF can help stop attackers from spoofing or hijacking the email domains of trusted senders, thus effectively taking away one method attackers use to fool their intended victims. DMARC, the combination of these two services, adds an extra layer of defence.
To learn more about Mimecast’s DMARC implementation and DNS Authentication policies please check out this document in Mimecaster Central community.
Data backups and business continuity
Preventive measures alone can’t keep up with the fast-evolving nature of ransomware attacks and as this attack highlights, there are many ways for an infection to enter an organisation.
It’s vital you regularly backup critical data and ensure that ransomware cannot spread to backup files. Ransomware can take time to encrypt large volumes of files, particularly across a network share. It is imperative to ensure your backup window is long enough to go back before any infection begins.
Backup & recovery measures only work after an attack, and cost organisations in downtime and IT resources dealing with the attack and aftermath.
Organisations must be able to continue to operate during the infection period and recover quickly once the infection has been removed.
Should firms ever pay a ransom?
We advise organisations never to succumb to the pressure to pay the ransom to regain access to their applications and data. There is no guarantee this will unlock files and further motivates and finances attackers to expand their ransomware campaigns.
