GHSA-7c6m-4442-2x6m

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:

// 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:

// 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):

// RowIterator.php:86
$this->endRow = $endRow ?: $this->subject->getHighestRow();

Notably, column attributes already have equivalent validation at line 161 (AddressRange::MAX_COLUMN_INT), and cell coordinates are validated in Coordinate::coordinateFromString() (line 40) against MAX_ROW. The row dimension attribute path bypasses both of these checks.

PoC

Step 1: Create the malicious XLSX file (~1.6KB)

import zipfile
import io

content_types = '<?xml version="1.0" encoding="UTF-8"?><Types...