Full Report
Microsoft has resolved a known issue that rendered the classic Outlook email client unusable for users who enabled the Microsoft Teams Meeting Add-in. [...]
Analysis Summary
# Vulnerability: Classic Outlook Client Crash via Teams Meeting Add-in
## CVE Details
- **CVE ID**: N/A (Functional Bug / Stability Issue)
- **CVSS Score**: N/A
- **CWE**: CWE-400 (Uncontrolled Resource Consumption / Service Interruption)
## Affected Systems
- **Products**: Microsoft Outlook (Classic), Microsoft Teams
- **Versions**:
- Outlook Version 2402 (Build 17328.20142) and lower.
- Microsoft Teams Meeting Add-in Build 1.26.02603.
- **Configurations**: Systems running older builds of Classic Outlook with the latest Teams Meeting Add-in enabled.
## Vulnerability Description
A compatibility regression exists between legacy builds of the Classic Outlook email client and the updated Microsoft Teams Meeting Add-in. When the newer add-in (Build 1.26.02603) is initialized by older Outlook binaries, it triggers a fatal application error, rendering the client unusable and forcing the application into a "Safe Mode" boot loop.
## Exploitation
- **Status**: Not exploited (Software defect/stability issue).
- **Complexity**: Low (Triggered by standard application use).
- **Attack Vector**: Local (Application interaction).
## Impact
- **Confidentiality**: None.
- **Integrity**: None.
- **Availability**: **High** (The email client becomes unusable for standard operation).
## Remediation
### Patches
- **Microsoft Teams Update**: Update to Version **26058.712.4527.9297** or higher.
- **Outlook Update**: Update Classic Outlook to the latest available Current Channel build (Version 2403 or higher).
### Workarounds
1. **Application Repair**: Perform an "Online Repair" of the Microsoft 365 installation via the Control Panel.
2. **Disable Add-in**:
- Launch Outlook in Safe Mode (Hold **Ctrl** while launching).
- Navigate to **File** > **Options** > **Add-ins**.
- Select **COM Add-ins** > **Go**.
- Uncheck **Microsoft Teams Meeting Add-in for Microsoft Office**.
- Restart Outlook normally.
## Detection
- **Indicators of Compromise**: Repeated application crashes upon launch; prompts to start in "Safe Mode" following a crash.
- **Detection Methods**: Monitor Event Viewer for Application Errors (Event ID 1000) involving `outlook.exe` and Teams-related DLLs. Review Microsoft 365 Health Dashboard for Incident **EX1254044**.
## References
- **Vendor Advisory**: [https[:]//support.microsoft[.]com/en-us/office/classic-outlook-crashes-and-opens-in-safe-mode-starting-march-12-2026-0f1b0427-e259-438d-aa93-78128ae61f80]
- **Incident Report**: [https[:]//admin.cloud.microsoft/] (Incident EX1254044)
- **BleepingComputer Report**: [https[:]//www.bleepingcomputer[.]com/news/microsoft/microsoft-fixes-outlook-classic-crashes-caused-by-teams-meeting-add-in/]