Microsoft Defender Antivirus Now Protects Users Against Ongoing Exchange Attacks

Microsoft informed customers on Thursday that Defender Antivirus and System Center Endpoint Protection now provide automatic protection against attacks exploiting the recently disclosed Exchange Server vulnerabilities.

Microsoft has released patches, detailed guidance, and a one-click mitigation tool to ensure that Exchange Server users are protected against attacks. The tech giant has now taken another step to protect customers who haven’t managed to install the available patches but who have Defender deployed on vulnerable servers.

The Exchange vulnerabilities are tracked as CVE-2021-26855, CVE-2021-26857, CVE-2021-26858 and CVE-2021-27065, and they are tracked as ProxyLogon. They can be exploited by an unauthenticated attacker to execute arbitrary code on targeted servers and gain access to emails and other sensitive information.

When Microsoft disclosed the flaws and announced patches in early March, it warned that a threat actor linked to China had been exploiting them in attacks. Roughly one week after disclosure, others reported that several cyberspy and cybercrime groups had started exploiting the vulnerabilities.

On March 12, Microsoft reported that more than 80,000 Exchange servers had still not been updated.

As threat actors increasingly start to target these vulnerabilities, Microsoft has now decided to release a security intelligence update for Defender Antivirus and System Center Endpoint Protection (build 1.333.747.0 or newer), which according to the company “breaks the attack chain by mitigating CVE-2021-26855,” the first vulnerability exploited in the ProxyLogon chain.

List of resources to help incident response teams and IT administrators respond to this global incident.

Microsoft described this as an “interim mitigation” that should help customers protect their systems until they can install the patches.

“Microsoft Defender Antivirus will automatically identify if a vulnerable version of Exchange Server is installed and apply the mitigations the first time the security intelligence update is deployed. The mitigation is deployed once per machine,” Microsoft explained.

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Related: Hackers Looking for Exchange Servers Affected by Recently Patched Flaw

Eduard Kovacs (@EduardKovacs) is a contributing editor at SecurityWeek. He worked as a high school IT teacher for two years before starting a career in journalism as Softpedia’s security news reporter. Eduard holds a bachelor’s degree in industrial informatics and a master’s degree in computer techniques applied in electrical engineering.