In an advisory, the Microsoft 365 Defender Team said: "...we have taken an additional step to further support our customers who are still vulnerable and have not yet implemented the complete security update.
"With the latest security intelligence update, Microsoft Defender Antivirus and System Centre Endpoint Protection will automatically mitigate CVE-2021-26855 on any vulnerable Exchange Server on which it is deployed.
"Customers do not need to take action beyond ensuring they have installed the latest security intelligence update (build 1.333.747.0 or newer), if they do not already have automatic updates turned on."
On 3 March, Microsoft disclosed that four zero-day exploits were being used to attack on-premises installations of Exchange Server.
Proof-of-concept code was released on GitHub on 10 March but was taken down by the Microsoft-owned code repository.
The code was again uploaded to GitHub a day or two later, by people other than the original poster.
However the company has not leaked any further information about claims emerging last Friday that exploit code for attacking Exchange Servers had been leaked by one of its own security partners, raising the possibility that this was a red herring.
The Wall Street Journal cited "people familiar with the matter" as making the claim. A wave of attacks used code similar to that which Microsoft provided to anti-virus companies on 23 February, the report claimed.
An information sharing program known as the Microsoft Active Protections Program was set up in 2008 and includes about 80 companies. Some of them were sent the code by Microsoft.
iTWire has sought comment from Microsoft as to why there has been no further word on this alleged leak. But there has been only silence from Redmond.
The Microsoft advisory said: "The Exchange security update is still the most comprehensive way to protect your servers from these attacks and others fixed in earlier releases.
"This interim mitigation is designed to help protect customers while they take the time to implement the latest Exchange Cumulative Update for their version of Exchange.
"Microsoft will provide guidance to our security partners so that they have the option to make available similar, simple mitigations in their products as well."
