IKEA has been working to contain a continuing phishing campaign that’s afflicting the furniture and houseware chain’s internal email system. BleepingComputer describes it as a “reply-chain email attack.” This form of attack is unusual but not unknown. The attackers obtain a legitimate corporate email and reply to it. “As the reply-chain emails are legitimate emails from a company,” BleepingComputer explains, “and are commonly sent from compromised email accounts and internal servers, recipients will trust the email and be more likely to open the malicious documents.”

“There is an ongoing cyber-attack that is targeting Inter IKEA mailboxes. Other IKEA organisations, suppliers, and business partners are compromised by the same attack and are further spreading malicious emails to persons in Inter IKEA,” explained an internal email sent to IKEA employees and seen by BleepingComputer.

“This means that the attack can come via email from someone that you work with, from any external organisation, and as a reply to an already ongoing conversations. It is therefore difficult to detect, for which we ask you to be extra cautious.”

The malicious emails have tended to trip filters designed to quarantine threats. But they’re convincing enough to induce employees to release them, quite innocently, from quarantine. IKEA is taking steps to preclude that possibility. IKEA has explained this to the retailer’s employees:

“Our email filters can identify some of the malicious emails and quarantine them. Due to that the email could be a reply to an ongoing conversation, it’s easy to think that the email filter made a mistake and release the email from quarantine. We are therefore until further notice disabling the possibility for everyone to release emails from quarantine.”

As is usually the case, a trained and well-informed employee seems to be the final line of defense. The malicious reply-chain emails do carry certain marks that might alert employees to the possibility they’re being subjected to phishing, and IKEA is working to raise awareness of those marks. For one thing, the links the phishing emails contain end with seven digits.

How the attackers have succeeded in compromising the email accounts isn’t clear. In other cases attackers have exploited ProxyShell and ProxyLogin vulnerabilities to compromise Microsoft Exchange Servers. IKEA has been tight-lipped about the incident, and it’s unknown whether the company’s internal servers were compromised.

New-school security awareness training can help your employees become alert to the threat posed by reply-chain attacks. BleepingComputer has the story.