Microsoft Confirms September Patch Tuesday Update Breaks Excel Copy-Paste Functionality.

Microsoft Confirms Excel Copy-Paste Failure Caused by September 2026 Security Update

Microsoft Corporation has officially acknowledged a widespread functionality bug affecting Microsoft Excel users following the deployment of the September 2026 Patch Tuesday security update. The flaw completely disrupts essential spreadsheet operations, leaving users unable to execute basic clipboard and formula commands across multiple desktop versions of the application.

Bug Mechanics and Affected Features

The flaw stems directly from security update KB5002914, which introduced unintended regression bugs into Excel’s core memory buffer and cell selection engine:

• Clipboard Failure Symptoms: When users attempt to copy data, the source cell selection border remains frozen in its original position. Upon executing a paste command, no data transfers to the destination cell, leaving target ranges entirely blank.

• Impact on Formula Replication and Autofill: Beyond standard copy-paste actions, the update breaks the Autofill feature and prevents users from click-and-dragging formula handles across contiguous row or column ranges.

• Broad Version Vulnerability: Microsoft confirmed that the bug impacts a wide range of perpetual and standalone volume-licensed installations, including Microsoft Excel 2024, Excel 2021, Excel 2019, and Excel 2016.

Root Cause Analysis and Temporary Workaround Mitigation

While engineering teams work on an emergency out-of-band security patch, Microsoft has issued temporary mitigation guidance for IT administrators and enterprise environments:

• Underlying Code Changes: Microsoft indicated that security adjustments within KB5002914 modified low-level memory allocation rules and inter-process communication protocols within the Office suite, inadvertently breaking how Excel handles clipboard buffer handles.

• Recommended Mitigation: Because an official hotfix has not yet been released, Microsoft advises impacted users and system administrators to temporarily uninstall security update KB5002914 via Windows Update settings or WSMC enterprise deployment consoles to restore normal spreadsheet functionality.

 

Source: Bleeping Computer 

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Microsoft Confirms Excel Copy-Paste Failure Caused by September 2026 Security Update

Microsoft Corporation has officially acknowledged a widespread functionality bug affecting Microsoft Excel users following the deployment of the September 2026 Patch Tuesday security update. The flaw completely disrupts essential spreadsheet operations, leaving users unable to execute basic clipboard and formula commands across multiple desktop versions of the application.

Bug Mechanics and Affected Features

The flaw stems directly from security update KB5002914, which introduced unintended regression bugs into Excel’s core memory buffer and cell selection engine:

• Clipboard Failure Symptoms: When users attempt to copy data, the source cell selection border remains frozen in its original position. Upon executing a paste command, no data transfers to the destination cell, leaving target ranges entirely blank.

• Impact on Formula Replication and Autofill: Beyond standard copy-paste actions, the update breaks the Autofill feature and prevents users from click-and-dragging formula handles across contiguous row or column ranges.

• Broad Version Vulnerability: Microsoft confirmed that the bug impacts a wide range of perpetual and standalone volume-licensed installations, including Microsoft Excel 2024, Excel 2021, Excel 2019, and Excel 2016.

Root Cause Analysis and Temporary Workaround Mitigation

While engineering teams work on an emergency out-of-band security patch, Microsoft has issued temporary mitigation guidance for IT administrators and enterprise environments:

• Underlying Code Changes: Microsoft indicated that security adjustments within KB5002914 modified low-level memory allocation rules and inter-process communication protocols within the Office suite, inadvertently breaking how Excel handles clipboard buffer handles.

• Recommended Mitigation: Because an official hotfix has not yet been released, Microsoft advises impacted users and system administrators to temporarily uninstall security update KB5002914 via Windows Update settings or WSMC enterprise deployment consoles to restore normal spreadsheet functionality.

 

Source: Bleeping Computer