Microsoft Patches Four Exchange Server Zero-Day Vulnerabilities Exploited in the Wild

Microsoft has issued out-of-band patches for multiple zero-day vulnerabilities exploited in the wild by a nation-state threat actor called HAFNIUM. Satnam Narang, Staff Research Engineer at Tenable says that by Microsoft choosing to patch these flaws out-of-band rather than including them as part of next week’s Patch Tuesday release leads us to believe the flaws are quite severe. Here’s a full analysis provided by Tenable along with a quote from Satnam Narang below.

Satnam Narang, Staff Research Engineer, Tenable shared his overview on this development, he said, “Four zero-day vulnerabilities in Exchange Server have been exploited in the wild by a nation-state threat actor called HAFNIUM. The fact that Microsoft chose to patch these flaws out-of-band rather than include them as part of next week’s Patch Tuesday release leads us to believe the flaws are quite severe even if we don’t know the full scope of those attacks.

“While Microsoft says that HAFNIUM primarily targets entities within the United States, other researchers say they have seen these vulnerabilities being exploited by different threat actors targeting other regions.

“Based on what we know so far, exploitation of one of the four vulnerabilities requires no authentication whatsoever and can be used to potentially download messages from a targeted user’s mailbox. The other vulnerabilities can be chained together by a determined threat actor to facilitate a further compromise of the targeted organization’s network.

“We expect other threat actors to begin leveraging these vulnerabilities in the coming days and weeks, which is why it is critically important for organizations that use Exchange Server to apply these patches immediately.”