EUVD-2026-309121

fkie_cve-2026-42267

Kimai is an open-source time tracking application. From version 2.27.0 to before version 2.54.0, any ROLE_USER can create a tag with a formula string as its name (e.g. =SUM(54+51)) via POST /api/tags and assign it to a timesheet. When an admin exports timesheets to XLSX, ArrayFormatter.formatValue() joins tag names with implode() and returns the result unchanged. OpenSpout promotes any =-prefixed string to a FormulaCell, writing <f>SUM(54+51)</f> into the XLSX archive. Excel evaluates the formula when the file is opened. This issue has been patched in version 2.54.0.

GHSA-3xc2-h5r3-wv3r — Kimai vulnerable to formula Injection via tag names in XLSX export

Affected: Packagist: kimai/kimai

## Summary

Any `ROLE_USER` can create a tag with a formula string as its name (e.g. `=SUM(54+51)`) via `POST /api/tags` and assign it to a timesheet. When an admin exports timesheets to XLSX, `ArrayFormatter.formatValue()` joins tag names with `implode()` and returns the result unchanged. OpenSpout promotes any `=`-prefixed string to a `FormulaCell`, writing `<f>SUM(54+51)</f>` into the XLSX archive. Excel evaluates the formula when the file is opened.

## Details

### 1. `ArrayFormatter` does not sanitize before returning

`sanitizeDDE()` exists on `StringHelper` and is called by `TextFormatter`, but `ArrayFormatter` never calls it. ```php // src/Export/Package/CellFormatter/ArrayFormatter.php:24 return implode(', ', $value); // no sanitizeDDE() call ```

### 2. Tag name validation does not block formula trigger characters

The API blocks commas in tag names but permits `=`, `+`, `-`, and `@` - all valid formula prefixes in Excel and LibreOffice Calc.

### 3. OpenSpout silently promotes strings to formula cells

`Cell::fromValue("=SUM(54+51)")` returns a `FormulaCell` with no warning.

### PoC

1. It logs in as normal user, creates tag `=SUM(54+51)`, assigns it to a timesheet. 2. Admin has to export timesheets to Excel version via `/en/export/` endpoint.

<img width="1304" height="128" alt="formula_injection_tags" src="https://github.com/use…

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EUVD-2026-309121

fkie_cve-2026-42267

GHSA-3xc2-h5r3-wv3r — Kimai vulnerable to formula Injection via tag names in XLSX export