Microsoft Reissues Microsoft Exchange Security Update to Patch Previously Identified Vulnerabilities

In mid-November, Microsoft released a routine security update for its Microsoft Exchange product line aimed at addressing various security vulnerabilities. However, enterprise IT administrators reported issues with email sending and receiving after deploying the update.

Microsoft later confirmed that the security update did impact customers using mail flow rules or Data Loss Prevention (DLP) policies, causing problems for both inbound and outbound emails. Issues included temporary server errors displayed by spam filters.

This led to all emails being queued in the spam server queue instead of being processed by the Microsoft Exchange server, severely affecting mail delivery.

In response, Microsoft withdrew the November 2024 security update to prevent further email communication issues from affecting more businesses. It was only recently that Microsoft resolved the bug and reissued the security update to address the vulnerabilities initially planned to be patched.

Microsoft advises IT administrators who had installed the previous security update to redeploy the new update (referred to as SUv2) to fix the bug affecting email delivery. However, the decision should be based on the specific circumstances of each enterprise.

Scenarios for IT Administrators:

• If you had manually installed the original November 2024 update (SUv1) and do not use transport or DLP rules, it is recommended to install the newly released update (SUv2) for more refined control over the X-MS-Exchange-P2FromRegexMatch header.
• If SUv1 was installed via Microsoft/Windows update and transport or DLP rules are not applicable, no action is needed for now. The December 2024 routine update will include the SUv2 update.
• If you had manually or automatically installed the original November 2024 update and then uninstalled it due to issues, you can now reinstall the SUv2 update.
• If the original November 2024 update was never installed, you can directly install the SUv2 update now.

It's worth noting that Microsoft has not yet deployed the SUv2 update through Microsoft/Windows updates, making it unavailable through the update check. The company plans to release it in the December 2024 update, so IT administrators should install the update directly at that time.