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Security advisories — Mar 08, 2021

Update 2: Multiple 0-Day Exploits Targeting on Premise Exchange Versions

2 minutes read
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THE THREAT

In response to the ongoing exploitation of recently disclosed Microsoft Exchange server zero-day vulnerabilities, Microsoft has released new mitigations for organizations that are currently unable to apply the required security patches. Importantly, Microsoft has also released the Microsoft Support Emergency Response Tool (MSERT). The MSERT tool can be used to detect and remediate known threats abusing these vulnerabilities.

Organizations are strongly recommended to ensure that security patches or mitigations are deployed to prevent exploitation. The MSERT tool should be used to help identify potentially malicious actions that may have occurred prior to patch or mitigation deployment.

What we’re doing about it

What you should do about it

Additional information

Confirmed vulnerable on-premises Microsoft Exchange Servers:

Exploited Vulnerabilities:

Microsoft has provided mitigations to defend against attacks exploiting all of the previously stated vulnerabilities. It should be noted that applying the mitigation actions will result in functionality degradation in Exchange servers. The functionality impact of each mitigation action is outline in detail in the official release. Microsoft has released a free Nmap script to scan for CVE-2021-26855.

References:

[1] https://msrc.microsoft.com/update-guide/releaseNote/2021-Mar

[2] https://msrc-blog.microsoft.com/2021/03/05/microsoft-exchange-server-vulnerabilities-mitigations-march-2021/

[3] https://docs.microsoft.com/en-us/windows/security/threat-protection/intelligence/safety-scanner-download

[4] https://github.com/microsoft/CSS-Exchange/blob/main/Security/http-vuln-cve2021-26855.nse

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