PhpSpreadsheet has CPU Denial of Service via Unbounded Row Number in XLSX Row Dimensions
Date: 2026-04
Affected: composer/phpoffice/phpspreadsheet, composer/phpoffice/phpspreadsheet, composer/phpoffice/phpspreadsheet
Attack vector: dos
Category: vulnerability-disclosure
Severity: High
CVE: CVE-2026-40902
CWE: CWE-400
CWE-770
CVSS: 7.5 (CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H)

## 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->getHighestRo


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