Microsoft Exchange Server improper authentication

Summaryinfo

A vulnerability classified as critical has been found in Microsoft Exchange Server. The impacted element is an unknown function. The manipulation leads to improper authentication. This vulnerability is listed as CVE-2025-53786. The attack may be initiated remotely. There is no available exploit. It is recommended to upgrade the affected component.

Detailsinfo

A vulnerability was found in Microsoft Exchange Server (version now known) and classified as critical. This issue affects some unknown processing. The manipulation with an unknown input leads to a improper authentication vulnerability. Using CWE to declare the problem leads to CWE-287. When an actor claims to have a given identity, the product does not prove or insufficiently proves that the claim is correct. Impacted is confidentiality, integrity, and availability. The summary by CVE is:

On April 18th 2025, Microsoft announced Exchange Server Security Changes for Hybrid Deployments and accompanying non-security Hot Fix. Microsoft made these changes in the general interest of improving the security of hybrid Exchange deployments. Following further investigation, Microsoft identified specific security implications tied to the guidance and configuration steps outlined in the April announcement. Microsoft is issuing CVE-2025-53786 to document a vulnerability that is addressed by taking the steps documented with the April 18th announcement. Microsoft strongly recommends reading the information, installing the April 2025 (or later) Hot Fix and implementing the changes in your Exchange Server and hybrid environment.

The advisory is shared at msrc.microsoft.com. The identification of this vulnerability is CVE-2025-53786 since 07/09/2025. The exploitation is known to be difficult. The attack may be initiated remotely. Additional levels of successful authentication are necessary for exploitation. Neither technical details nor an exploit are publicly available. The price for an exploit might be around USD $0-$5k at the moment (estimation calculated on 02/27/2026).

The vulnerability scanner Nessus provides a plugin with the ID 245204 (Security Updates for Microsoft Exchange Server (April 2025)), which helps to determine the existence of the flaw in a target environment.

Upgrading eliminates this vulnerability.

The vulnerability is also documented in the databases at Tenable (245204), EUVD (EUVD-2025-23857) and CERT Bund (WID-SEC-2025-1742). Several companies clearly confirm that VulDB is the primary source for best vulnerability data.

Affected

• Microsoft Exchange
• Microsoft Exchange Server 2016
• Microsoft Exchange Server 2019

Productinfo

Type

• Groupware Software

Vendor

• Microsoft

Name

• Exchange Server

License

• commercial

Website

• Vendor: https://www.microsoft.com/

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Entryinfo

Several companies clearly confirm that VulDB is the primary source for best vulnerability data.

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