Excel paste fails silently after Microsoft's September security update

[Redaktion]

Microsoft's September security update stops Excel from pasting. The command fails without a beep and without an error message, and the destination cell stays empty. Microsoft added the bug to its own update description on September 10 and says it is still researching the cause. Excel 2016, 2019, 2021 and 2024 are affected.

https://www.notebookcheck.net/Excel-paste-fails-silently-after-Microsoft-s-September-security-update.1398881.0.html

[Bill]

This issue has been driving me crazy. Good to know the source.

[Drac]

**Subject: Excel LTSC 2024 16.0.17932.20996 – Copy/Paste fails when copying FROM a worksheet containing Conditional Formatting**

I found a reproducible Copy/Paste regression in Excel LTSC 2024 build 16.0.17932.20996.

The important detail is that the problem is **specific to copying FROM a worksheet that contains Conditional Formatting**. It does not affect the whole workbook.

### Minimal reproduction

1. Create a new blank workbook.
2. Create two worksheets:

   * Sheet1: no Conditional Formatting.
   * Sheet2: add a simple Conditional Formatting rule to one cell.
3. Enter `hello` in a cell on Sheet1.
4. Copy Sheet1 → Sheet2: **works correctly**.
5. Enter `hello` in a cell on Sheet2.
6. Copy Sheet2 → Sheet1 or Sheet2: **Copy/Paste silently fails**.
7. The same failure occurs when copying a newly created cell containing only plain text; it is not related to formulas or the cell contents.

I also reproduced the problem in an existing, long-standing `.xlsm` workbook. A worksheet containing Conditional Formatting could not be copied from normally, even when the source cell contained only simple text.

Interestingly:

* Copying **Values** from the affected worksheet works.
* Copying **Formulas** works.
* Copying **Formats** fails.
* Normal Copy/Paste fails.
* Copying from a worksheet without Conditional Formatting into the affected worksheet works.

### Workaround / confirmation

I rolled back Office LTSC 2024 from:

**16.0.17932.20996 → 16.0.17932.20910**

using Click-to-Run.
"C:\Program Files\Common Files\Microsoft Shared\ClickToRun\OfficeC2RClient.exe" /update user updatetoversion=16.0.17932.20910


After the rollback, both:

* the minimal test workbook, including Copy/Paste after adding Conditional Formatting, and
* the original affected workbook

work correctly again.

This strongly suggests a regression introduced after build 16.0.17932.20910, specifically involving Copy/Paste from worksheets containing Conditional Formatting.

Environment:

* Windows 11 Pro 25H2
* Microsoft Office LTSC Standard 2024
* Affected build: 16.0.17932.20996
* Working build: 16.0.17932.20910