PhpSpreadsheet is a pure PHP library for reading and writing spreadsheet files. Prior to 1.30.4, 2.1.16, 2.4.5, 3.10.5, and 5.7.0, the XLSX reader's ColumnAndRowAttributes::readRowAttributes() method reads row numbers from XML attributes without validating them against the spreadsheet maximum row limit (AddressRange::MAX_ROW = 1,048,576). An attacker can craft a minimal XLSX file (~1.6KB) containing a <row r="999999999"/> element that inflates cachedHighestRow to 999,999,999, causing any subsequent row iteration to attempt ~1 billion loop cycles and exhaust CPU resources. This vulnerability is fixed in 1.30.4, 2.1.16, 2.4.5, 3.10.5, and 5.7.0.

Affected: Packagist: phpoffice/phpspreadsheet

## Summary

The XLSX reader's `ColumnAndRowAttributes::readRowAttributes()` method reads row numbers from XML attributes without validating them against the spreadsheet maximum row limit (`AddressRange::MAX_ROW = 1,048,576`). An attacker can craft a minimal XLSX file (~1.6KB) containing a `<row r="999999999"/>` element that inflates `cachedHighestRow` to 999,999,999, causing any subsequent row iteration to attempt ~1 billion loop cycles and exhaust CPU resources.

## Details

In `src/PhpSpreadsheet/Reader/Xlsx/ColumnAndRowAttributes.php` at line 216, the row index is cast directly from XML without bounds checking:

```php // ColumnAndRowAttributes.php:216 $rowIndex = (int) $row['r']; // No validation against AddressRange::MAX_ROW ```

This value flows through `setRowAttributes()` (line 126) → `$this->worksheet->getRowDimension($rowNumber)` (line 60), which updates the cached highest row in `Worksheet.php:1348`:

```php // Worksheet.php:1342-1349 public function getRowDimension(int $row): RowDimension { if (!isset($this->rowDimensions[$row])) { $this->rowDimensions[$row] = new RowDimension($row); $this->cachedHighestRow = max($this->cachedHighestRow, $row); } return $this->rowDimensions[$row]; } ```

The inflated `cachedHighestRow` is then returned by `getHighestRow()` (line 1099) and used as the default end bound in `RowIterator::resetEnd()` (RowIterator.php:86):

```php // RowIterator.php:86 $this->endRow = $endRow ?: $this->subject->getHighestR…