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Attackers Are Landing Email Inboxes Without the Need to Phish

We’ve all heard the proverb: Give a man a fish and you feed him for a day. Teach a man to fish and you feed him for a lifetime. Well now, threat actors don’t even have to exert the effort to phish to land business email accounts. 

We’ve all heard the proverb: Give a man a fish and you feed him for a day. Teach a man to fish and you feed him for a lifetime. Well now, threat actors don’t even have to exert the effort to phish to land business email accounts. 

According to an alert published earlier this year by the FBI, Business Email Compromise (BEC) and Email Account Compromise (EAC) have caused $12 billion in losses since October 2013. Traditionally, social engineering and intrusion techniques have been the most common ways to gain access to business email accounts and dupe individuals to wire funds to an attacker-controlled account. These methods play out as follows:

1. Social engineering and email spoofing: Attackers will use social engineering to pose as a colleague or business partner and send fake requests for information or the transfer of funds. These emails can be quite convincing as the attacker makes a significant effort to identify an appropriate victim and register a fake domain, so that at first glance the email appears to belong to a colleague or supplier. 

2. Account takeover: Here, attackers use information-stealing malware and key loggers to gain access to and hijack a corporate email account, which they then use to make fraudulent requests to colleagues, accounting departments and suppliers. They can also alter mailbox rules so that the victim’s email messages are forwarded to the attacker, or emails sent by the attacker are deleted from the list of sent emails. 

These techniques have served threat actors well for quite some time. But now we are seeing new, more expeditious methods emerge to gain access to business email accounts. Compromised credentials being offered on criminal forums, exposed through third-party compromises, or vulnerable through misconfigured backups and file sharing services, make the opportunity to profit from BEC easier than ever. Email inboxes are also being used not just to request wire transfers, but to steal financially-sensitive information stored within these accounts or to request information from other employees. With declining barriers to entry for BEC, and more ways to monetize this type of fraud, we can expect the losses to continue to rise and perhaps even accelerate in the near term.

Here’s how these alternative methods work:

1. Paying for access. It’s common for accounts to be shared and sold across criminal forums, and the emails of finance departments and CEO/CFOs are no exception. It’s even possible to outsource this work to online actors who will acquire company credentials for a percentage of earnings or a set fee beginning as low as $150.

2. Getting lucky with previously compromised credentials. As I’ve discussed before, individuals will often reuse passwords across multiple accounts. In our research we’ve detected more than 33,000 finance department email addresses exposed within our own third-party data breach repository 83 percent of which had passwords associated. With many email and password combinations of finance department email accounts already compromised, cybercriminals can get lucky.

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3. Searching across misconfigured archives and file stores. Inboxes, particularly those of finance departments and CEO/CFOs, are replete with financially-sensitive information such as contract scans, purchase orders, and payroll and tax documents. This information can be used for fraud or re-sold on forums and marketplaces. The sad reality is that there’s no need to go to a dark web market when sensitive data is available for free on the open web. Employees and contractors sometimes turn to easy, rather than secure, ways of archiving their emails. We identified that more than 12.5 million email archive files and 50,000 emails that contained “invoice”, “payment” or “purchase order” have been exposed due to unauthenticated or misconfigured file stores.

Regardless of the method attackers use to perform a BEC scam, these seven security measures can help to mitigate the risks. 

1. Update your security awareness training content to include the BEC scenario. This should be a part of new hire training, but you should conduct ad-hoc training for this scenario now. 

2. Build BEC into your contingency plans, just as you have built ransomware and destructive malware into your incident response/business continuity planning.

3. Work with your wire transfer application vendors to build in manual controls as well as multiple person authorizations to approve significant wire transfers.

4. Monitor for exposed credentials. This is crucial for your finance department email, but it’s important for all user accounts. Multifactor authentication will also increase the difficulty for attackers to perform account takeovers. 

5. Conduct ongoing assessments of your executives’ digital footprints. You can start with using Google Alerts to track new web content related to them.

6. Prevent email archives from being publicly exposed. For services like Server Message Block (SMB), rsync and the File Transfer Protocol (FTP), use a strong, unique password and disable guest or anonymous access and firewall the port off from the Internet. If it needs to be on the Internet or without a password, then make sure you whitelist the IPs which are expressly permitted to access the resource.

7. Be aware of the risks of contractors who back up their emails on Network Attached Storage (NAS) devices. Users should add a password and disable guest/anonymous access, as well as opt for NAS devices that are secured by default. Ideally, organizations should provide training on the risks of using home NAS drives, as well as offer backup solutions so that contractors and employees don’t feel the need to backup their devices at home.

BEC is becoming increasingly profitable for threat actors as organizations are making it easy for adversaries to gain access to the valuable information that sits within these inboxes. However, with the right combination of people, processes and technology, organizations can mitigate the risk.

Written By

Alastair Paterson is the CEO and co-founder of Harmonic Security, enabling companies to adopt Generative AI without risk to their sensitive data. Prior to this he co-founded and was CEO of the cyber security company Digital Shadows from its inception in 2011 until its acquisition by ReliaQuest/KKR for $160m in July 2022. Alastair led the company to become an international, industry-recognised leader in threat intelligence and digital risk protection.

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