This week Microsoft has released emergency out-of-band security updates that address four zero-day issues (CVE-2021-26855, CVE-2021-26857, CVE-2021-26858, and CVE-2021-27065) in all supported MS Exchange versions that are actively exploited in the wild.
In response to the disclosure, the US Cybersecurity and Infrastructure Security Agency (CISA) has issued the Emergency Directive 21-02 in response to the disclosure of zero-day vulnerabilities in Microsoft Exchange.
Microsoft revealed that at least one China-linked APT group, tracked as HAFNIUM, chained these vulnerabilities to access on-premises Exchange servers to access email accounts, and install backdoors to maintain access to victim environments.
The US CISA’s emergency directive orders federal agencies to urgently update or disconnect MS Exchange on-premises installs.
Researchers at the MS Exchange Server team have released a script that could be used by administrators to check if their installs are vulnerable to the recently disclosed vulnerabilities.
Microsoft released the tool as open-source on GitHub, it can be used to check the status of Exchange servers.
“Formerly known as Test-Hafnium, this script automates all four of the commands found in the Hafnium blog post.” states Microsoft. “It also has a progress bar and some performance tweaks to make the CVE-2021-26855 test run much faster.
Download the latest release here: Download Test-ProxyLogon.ps1
The most typical usage of this script is to check all Exchange servers and save the output,”
The script automates the tests for the four zero-day vulnerabilities in Microsoft Exchange Server.
“CISA is aware of widespread domestic and international exploitation of these vulnerabilities and strongly recommends organizations run the Test-ProxyLogon.ps1 script—as soon as possible—to help determine whether their systems are compromised. For additional information on the script, see Microsoft’s blog HAFNIUM targeting Exchange Servers with 0-day exploits.”
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(SecurityAffairs – hacking, MS Exchange)