Microsoft updates mitigation for ProxyNotShell Exchange zero days

Microsoft has updated the mitigations for the latest Exchange zero-day vulnerabilities tracked as CVE-2022-41040 and CVE-2022-41082, also referred to ProxyNotShell.

Reported privately to Microsoft three weeks ago, CVE-2022-41040 is a server-side request forgery that enables privilege escalation and works with CVE-2022-41082 to trigger remote code execution on on-premise Exchange server deployments.

Since the proposed URL blocking rule was too specific, adversaries could still exploit the Exchange vulnerabilities in new attacks.

On Tuesday, Microsoft announced that it updated its advisories with the improved URL Rewrite rule, recommending Exchange Server customers review it and adopt one of the three mitigation options provided.

Customers with Exchange Emergency Mitigation Service enabled benefit automatically from the updated URL Rewrite mitigation for Exchange Server 2016 and Exchange Server 2019.

It is worth noting that Microsoft provides these mitigations for customers with on-premise Exchange servers, which means that companies with a hybrid deployment are also at risk.

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