CVE-2021-34523Vulnerability
Microsoft Exchange Server Privilege Escalation Vulnerability
Reported by 3 independent sources · first reported by Group-IB · last reported
Last reported 4 years ago
Fix due 17 Nov 2021
Used by ransomware: knownCISA KEV catalogue
higher than 99% of CVEsFIRST EPSS, as of 26 Sep 2026
What the reports say
3 reports, newest first · the exact sentence from each-
Detection and response for the actively exploited ProxyShell vulnerabilities“…y Agency (CISA) released an urgent notice related to the exploitation of ProxyShell vulnerabilities (CVE-2021-31207, CVE-2021-34473, CVE-2021-34523).”
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Microsoft Exchange Servers Still Vulnerable to ProxyShell“CVE-2021-34523 enables malicious actors to execute arbitrary code post-authentication on Microsoft Exchange servers due to a flaw in the PowerShell service not properly validating access tokens.”
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BlackCat Ransomware: Tactics, Techniques & Mitigation Strategies“In the case of BlackCat, the attackers exploited a set of vulnerabilities known as ProxyShell (CVE-2021-34473, CVE-2021-34523, CVE-2021-31207), which enabled them to place a web shell on a vulnerable Microsoft Exchange server and then conduct post-exploitation activities.”
Indicators reported together
named in the same reportsAlso named with it: CVE-2021-34473, CVE-2021-31207
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