News

Microsoft Warns E-Mail Users of Months-Long Security Attack

• By Kurt Mackie
• April 15, 2019

Some users of Microsoft's e-mail services may have had their accounts exposed to "individuals outside Microsoft" over the past three months, the company admitted recently.

Microsoft warned its customers of the breach on Friday in a letter that was reproduced on a Reddit forum. The breach happened between Jan. 1 and March 28, according to the letter, and occurred because "a Microsoft support agent's credentials were compromised." The outside parties were able to view things like users' e-mail addresses and their correspondents, as well as folder names and subject-line content.

Microsoft had suggested in its letter that the attackers could not read the contents of peoples' e-mails. However, it later backtracked on that statement. So far, there appears to be no general information about the breach published by Microsoft, apart from the letter it sent to affected users.

Login credentials weren't exposed, according to Microsoft's letter. It nevertheless recommended that affected e-mail users should "reset your passwords" and be wary of getting e-mails with misleading domain names.

Microsoft told TechCrunch that "a limited consumer accounts were impacted, and we have notified all impacted customers." According to that Saturday-posted TechCrunch story, no business customers were affected.

A Motherboard story, citing an unnamed source, indicated that Hotmail, MSN and Outlook accounts were affected and the attackers could access e-mail content. In response, Microsoft confirmed to Motherboard that the attackers had gained access to the e-mail contents of some users, but that just six percent of the total was so affected. Motherboard's source also indicated that the attackers had access for six months, in contrast to the three months claimed by Microsoft.

Microsoft isn't disclosing how many accounts were affected by the breach, but it disabled the compromised credentials to block attacker access, according to a story by The Verge.

Targeting a privileged account, such as an accounted held by a Microsoft support agent, is a common tactic of attackers, according to Ilia Kolochenko, founder and CEO of Geneva-based Web security company ImmuniWeb (formerly High-Tech Bridge).

"Compromise of privileged accounts is a widespread and effective method among cybercriminals to get to the crown jewels at high speed and low cost," Kolochenko indicated in an e-mailed statement. "It is, however, quite surprising that such a reputable company as Microsoft reportedly has not reacted to the anomalies for as long as three months."

The typical defense is for organizations to monitor their privileged accounts. It's a fairly easy task to do given current machine learning technologies, Kolochenko added.

In the meantime, Kolochenko recommended that all Outlook users should change their passwords, including the passwords on other accounts that were used for Outlook account recovery purposes.

"As a precaution, all Outlook users should change their passwords and secret questions, as well as passwords for any other accounts that sent, or could have sent, a password recovery link to their Outlook email."

According to Motherboard's source, a possible motivation of the attackers was to gain access to account recovery information in order to unlock stolen iPhones.