Chinese Outlook users hit by eavesdropping attack

Weeks after the Chinese government blocked Gmail, some Outlook users in the country have reported suspicious attempts to intercept their email and passwords.

According to, a group that monitors blocked websites in China, a man-in-the-middle attack on Outlook users in China is likely the work of Chinese authorities.

The attack, which lasted one day from January 17, was aimed at mobile and desktop email clients that connect to Microsoft’s Outlook servers via IMAP and SMTP. According to, Outlook web interfaces were unaffected.

While a successful attack could allow an attacker to log an Outlook user’s passwords, email and contacts, the victim would have to ignore or miss a certificate error warning in an email client before connecting to the attacker’s server.

It’s not known why Outlook web interfaces were not targeted, however points out that warning messages in email clients, such as the iOS Mail client, are less overt than warnings in modern web browsers. The attacks were therefore “especially devious” and may mean authorities are gauging the effectiveness of the attacks.

"By keeping track of how many users ignore the certificate warnings, the authorities will be able to determine the effectiveness of this type of attack," noted.

The censorship watchdog said the attacks may signal that Chinese authorities are cracking down on communications that aren’t easily monitored.

Late last year, shortly after reported an MITM attack on iCloud users, Apple issued a warning to English and Chinese language users that it was aware of “intermittent attacks” that rely on issuing bogus encryption certificates to users.

More recently, China restricted access to Gmail and according to Google’s Transparency Report, today traffic remains significantly lower than in 2014. A round of disruptions to Gmail began ahead of the 10 year anniversary of the Tiananmen Square protests last year. As noted by Reuters, before the near total blockade at the end of last year, Gmail users were still able to access Gmail through email clients operating through protocols IMAP, SMTP and POP3.

This article is brought to you by Enex TestLab, content directors for CSO Australia.

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