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Microsoft Confirms Exploitation of Two Exchange Server Zero-Days

Microsoft has confirmed that it’s aware of two Exchange Server zero-day vulnerabilities that have been exploited in targeted attacks. The tech giant is working on patches.

GTSC, a cybersecurity company based in Vietnam, reported seeing attacks exploiting two new Microsoft Exchange zero-day vulnerabilities. The firm believes the attacks, which were first seen in August and aimed at critical infrastructure, were launched by a Chinese threat group.

ProxyNotShellTechnical details on the vulnerabilities have not been made public, but GTSC did say that the threat actor’s post-exploitation activities included the deployment of backdoors, lateral movement, and the delivery of malware.

The vulnerabilities were reported to Microsoft through Trend Micro’s Zero Day Initiative (ZDI). Microsoft has now published a blog post to inform customers that it is investigating two reported zero-day flaws.

The tech giant says one of the flaws is a server-side request forgery (SSRF) issue tracked as CVE-2022-41040 and the second is a remote code execution vulnerability tracked as CVE-2022-41082. The security holes have been found to impact Exchange Server 2013, 2016 and 2019.

“At this time, Microsoft is aware of limited targeted attacks using the two vulnerabilities to get into users’ systems. In these attacks, CVE-2022-41040 can enable an authenticated attacker to remotely trigger CVE-2022-41082. It should be noted that authenticated access to the vulnerable Exchange Server is necessary to successfully exploit either of the two vulnerabilities,” Microsoft said.

The company is working on an accelerated timeline to patch the vulnerabilities. In the meantime, it has provided detailed guidance on how exploitation can be prevented. Microsoft says its security products should detect post-exploitation malware and activity associated with these attacks. Microsoft Exchange Online customers do not need to take any action.

Security researcher Kevin Beaumont has named the vulnerabilities ProxyNotShell due to similarities with the old ProxyShell flaw, which has been exploited in the wild for more than a year. In fact, before Microsoft confirmed the zero-days, Beaumont believed it might just be a new and more effective variant of the ProxyShell exploit, rather than an actual new vulnerability.

Other researchers also believe the vulnerabilities could be related to Microsoft not completely killing ProxyShell.

Related: Hackers Deploying Backdoors on Exchange Servers via ProxyShell Vulnerabilities

Related: Zero-Days Under Attack: Microsoft Plugs Exchange Server, Excel Holes

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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.