The email marketing service MailChimp employs security controls to ensure that its customers do not use the service to send spam; yet, this week malicious spam emails were sent from multiple accounts after a MailChimp account hack.
Customer accounts that were breached included Business News Australia, Brisbane’s The Sit Down Comedy Club, and gardening and home services provider Jim’ Group.
MailChimp accounts are valuable to spammers as subscribers to company newsletters are more likely to trust the emails than they would an email from an unknown sender. The hijacked accounts were used to send spam emails demanding an invoice be paid. Spammers often target businesses with malicious emails that spread malware. If malware such as a keylogger can be installed, the attackers can gain access to corporate email accounts or gain network access. Corporate bank account details can be stolen and fraudulent transfers made.
A fake invoice is a common ploy used to fool email recipients into opening an infected email attachment or clicking on a malicious link. A sense of urgency is often included to scare the recipient into opening the attachment. A threat of legal action if the outstanding invoice is not paid promptly is a common tactic.
In this case, a number of different variants were sent. Some emails contained an image with an embedded hyperlink which recipients could click to view the invoice. The spammers also included the logo of accounting software Quickbooks for extra authenticity.
Initially, it appeared that MailChimp had experienced a security breach that resulted in spammers gaining access to accounts; although the company issued a statement saying that an investigation of the incident did not point to an internal breach.
MailChimp told Motherboard “MailChimp’s normal compliance processes identified and disabled a small number of individual accounts sending fake invoices. We have investigated the situation and have found no evidence that MailChimp has been breached. The affected accounts have been disabled, and fraudulent activity has stopped.”
How the MailChimp account hack was pulled off remains a mystery. The spammers may have managed to guess the passwords that were used to secure accounts or they could have obtained those passwords by other means. The practice of reusing passwords on multiple platforms could be to blame. If a breach of one platform occurs, cybercriminals can gain access to all other online services that use the same password.
In a recent post, computer security blogger Graham Cluley suggested some passwords were obtained by the password stealing Trojan Vawtrak. Cluley was contacted by an anonymous source who claimed to be in possession of two thousand MailChimp login credentials which were recorded by Vawtrak.
Details of the MailChimp account hack are unlikely to be released, although the incident shows how important it is for businesses to use two-factor authentication to secure their online accounts. The incident also shows how important it is to exercise caution and to treat any email attachment of hyperlink as potentially malicious, even if the sender of the email is known.