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Microsoft new Outlook Excel attachment opening issue

Service Disruption
First reported
Last updated
Happening score
H score 13
1 unique sources, 1 articles

Summary

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The new Outlook client is experiencing a service disruption that can block users from opening Excel email attachments, interrupting routine file access. The issue has affected Exchange Online customers since at least November 23rd and is tied to an encoding error in file names. A fix has been deployed and is being validated, while users may need to use Outlook on the web or download the file locally.

Related Happenings

Microsoft Exchange CVE-2026-42897 mitigation advisory

Advisory/Mitigation
First: 15.05.2026 12:40 Last: 15.05.2026 12:40 Sources 1

About this happening: **Microsoft** issued immediate mitigation guidance for **CVE-2026-42897**, reducing risk for **Exchange Server 2016, 2019, and Subscription Edition (SE)** on-premises servers that...

Latest development: 15.05.2026 15:35

Microsoft issued temporary mitigation guidance for CVE-2026-42897 while a patch is still in development, recommending the Exchange Emergency Mitigation (EM) Service, which is enabled by default and can be checked with the Exchange Health Checker script, or the Exchange On-premises Mitigation Tool (EOMT) for disconnected or air-gapped environments. Microsoft noted that the mitigations can disrupt features such as OWA Print Calendar and Inline images, and that servers older than March 2023 cannot receive new mitigations through EM Service.

Open Happening

Microsoft Exchange Server spoofing/XSS flaw under active exploitation (CVE-2026-42897)

Vulnerability
First: 15.05.2026 09:19 Last: 15.05.2026 09:19 Sources 1

About this happening: **CVE-2026-42897** is an **actively exploited** **spoofing/XSS** flaw in **on-premises Microsoft Exchange Server** that can let attackers trigger **arbitrary JavaScript** in a bro...

Open Happening

Microsoft Windows 365 Office installation disruption

Service Disruption
First: 13.05.2026 14:53 Last: 13.05.2026 14:53 Sources 1

About this happening: The **Windows 365** service update has introduced a **configuration change** that is blocking **Office downloads and installs** for some customers, disrupting access on cloud PCs....

Open Happening

Microsoft May 2026 Patch Tuesday (120 flaws)

Security Patch Release
First: 12.05.2026 21:08 Last: 12.05.2026 21:08 Sources 1

About this happening: **Microsoft** released its **May 2026 Patch Tuesday** updates, fixing **120 flaws** and disclosing **no zero-days**. The bundle includes **17 Critical** vulnerabilities, with mult...

Open Happening

Microsoft Classic Outlook email sending disruption

Service Disruption
First: 02.04.2026 12:12 Last: 02.04.2026 12:12 Sources 1

About this happening: **Microsoft** is investigating a **Classic Outlook** disruption that can prevent some users from sending or replying to email through **Outlook.com**, causing **NDR errors** and m...

Latest development: 06.04.2026 22:19

Microsoft fixed a known issue affecting some Classic Outlook users sending emails via Outlook.com that could return non-delivery reports (NDRs) with 0x80070005-0x0004dc-0x000524 errors. Microsoft said the service change was in production as of April 3, 2026, and advised affected users to use the New Outlook client or Outlook.com on the web; Microsoft also pointed users to downloading the Outlook Address Book for affected Outlook.com accounts.

Open Happening

Timeline

  1. 01.12.2025 19:42 1 articles · 5mo ago

    Microsoft acknowledges new Outlook Excel attachment issue

    Initial Disclosure

    Microsoft acknowledged a service issue in the new Outlook client that can prevent Exchange Online customers from opening Excel email attachments when filenames contain non-ASCII characters, and said the problem had affected customers since at least November 23rd.

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  2. 01.12.2025 19:42 2 articles · 5mo ago

    Microsoft deploys fix for the new Outlook Excel attachment issue

    Mitigation Patch Update

    Microsoft said it has deployed a fix for the missing-encoding problem in Excel file names, is validating the deployment, and advised affected users to open the file in Outlook on the web or download it locally.

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