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Response snapshot Oct 27, 2026, 03:42 UTC

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VulnerabilityCVE-2026-40863

PhpSpreadsheet has CPU Denial of Service via Unbounded Row Index in SpreadsheetML XML Reader

The SpreadsheetML XML reader (`Reader\Xml`) does not validate the `ss:Index` row attribute against the maximum allowed row count (`AddressRange::MAX_ROW = 1,048,576`).

Published Updated

At a glance

Exploited
Not known
Severity
7.5 High (CVSS 3.1)
Chance of exploitation
0.4% in the next 30 days
Sources
2 independent sources

What to do

GitHub lists first patched versions: phpoffice/phpspreadsheet: 5.7.0; phpoffice/phpspreadsheet: 3.10.5; phpoffice/phpspreadsheet: 2.4.5; phpoffice/phpspreadsheet: 2.1.16; phpoffice/phpspreadsheet: 1.30.6. Confirm the affected range and upgrade guidance in the exact advisory.

Read GitHub-reviewed advisory GHSA-84wq-86v6-x5j6 (opens a new tab)

What happened

## Summary

The SpreadsheetML XML reader (`Reader\Xml`) does not validate the `ss:Index` row attribute against the maximum allowed row count (`AddressRange::MAX_ROW = 1,048,576`). An attacker can craft a SpreadsheetML XML file with `ss:Index="999999999"` on a ` ` element, which inflates the internal `cachedHighestRow` to ~1 billion. Any subsequent call to `getRowIterator()` without an explicit end row will attempt to iterate ~1 billion rows, causing CPU exhaustion and denial of service.

## Details

In `src/PhpSpreadsheet/Reader/Xml.php`, the `loadSpreadsheetFromFile` method processes ` ` elements:

Continue reading

```php // Xml.php:397-402 if (isset($row_ss['Index'])) { $rowID = (int) $row_ss['Index']; // No validation against MAX_ROW } if (isset($row_ss['Hidden'])) { $rowVisible = ((string) $row_ss['Hidden']) !== '1'; $spreadsheet->getActiveSheet()->getRowDimension($rowID)->setVisible($rowVisible); } ```

The `$rowID` value read from `ss:Index` is cast to int with no upper bound check. It is then passed to `getRowDimension()`:

```php // Worksheet.php:1342-1351 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]; } ```

This inflates `cachedHighestRow` to the attacker-controlled value. Additionally, at line 412, `$cellRange = $columnID . $rowID` is constructed and passed to `getCell()`, which calls `createNewCell()` (Worksheet.php:1294) and also sets `cachedHighestRow`.

The `RowIterator` constructor uses `getHighestRow()` as its default end row:

```php // RowIterator.php:84-88 public function resetEnd(?int $endRow = null): static { $this->endRow = $endRow ?: $this->subject->getHighestRow(); return $this; } ```

With `cachedHighestRow` at ~1 billion, iterating over rows causes CPU exhaustion. The `DefaultReadFilter` provides no protection — it returns `true` for all cells.

Even without the `Hidden` attribute, any cell data within the row still uses the inflated `$rowID` at line 412, so the `ss:Hidden` attribute is not required to trigger the vulnerability.

## PoC

1. Create `poc.xml`: ```xml

test

```

2. Load and iterate: ```php load('poc.xml'); $sheet = $spreadsheet->getActiveSheet();

echo "Highest row: " . $sheet->getHighestRow() . "\n"; // Outputs: Highest row: 1000000000

// This loop will attempt ~1 billion iterations → CPU exhaustion foreach ($sheet->getRowIterator() as $row) { // Never completes } ```

## Impact

Any PHP application that processes user-uploaded SpreadsheetML XML files using PhpSpreadsheet is vulnerable. An attacker can cause denial of service by:

- Exhausting server CPU with a single small XML file (~300 bytes) - Blocking the PHP worker process, potentially affecting all concurrent users - Triggering PHP max_execution_time limits that still consume resources before killing the process

The attack requires no authentication — only the ability to upload or cause the application to process a crafted SpreadsheetML file.

## Recommended Fix

Add MAX_ROW validation after reading the `ss:Index` attribute in `src/PhpSpreadsheet/Reader/Xml.php`:

```php // After line 398: if (isset($row_ss['Index'])) { $rowID = (int) $row_ss['Index']; if ($rowID > AddressRange::MAX_ROW) { $rowID = AddressRange::MAX_ROW; } } ```

Add the necessary import at the top of the file: ```php use PhpOffice\PhpSpreadsheet\Cell\AddressRange; ```

The same validation should also be applied to the `ss:Index` attribute on ` ` elements (line 409) for the column dimension.

Affected package ranges reported by GitHub: phpoffice/phpspreadsheet: >= 4.0.0, <= 5.6.0 phpoffice/phpspreadsheet: >= 3.3.0, <= 3.10.4 phpoffice/phpspreadsheet: >= 2.2.0, <= 2.4.4 phpoffice/phpspreadsheet: >= 2.0.0, <= 2.1.15 phpoffice/phpspreadsheet: <= 1.30.5

Scores and how they were measured

CVSS base severity

7.5

Version 3.1As of

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

Measurement source (opens a new tab)

How bad it is if exploited. Not a prediction of exploitation or proof you are exposed.

EPSS probability

0.4%

Scored Percentile 33.5%

Model and measurement source (opens a new tab)

A model's estimate of exploitation in the next 30 days, not certainty or your own risk.

Related technology

Sources

  1. Primary source

    GitHub-reviewed advisory GHSA-84wq-86v6-x5j6 (opens a new tab)

    The public advisory supplies the description, affected package/version ranges, and any listed CVSS metric. GitHub review is not local review.

    Published Checked

  2. Primary source

    GitHub public advisory API page (opens a new tab)

    The API page supplied GHSA-84wq-86v6-x5j6, its actual identifiers, source dates, and structured metrics.

    Published Date not suppliedChecked

  3. Primary source

    NVD CVE-2026-40863 (opens a new tab)

    NVD record: description, CVSS (the CNA score is preferred), affected products, and publication date. Not evidence of exploitation.

    Published Checked

  4. Primary source

    Vendor advisory (via NVD references) (opens a new tab)

    The vendor advisory referenced by the CVE record, for affected versions and fixes.

    Published Date not suppliedChecked

  5. Primary source

    NVD CVE API 2.0 (opens a new tab)

    The NVD API page that supplied this CVE record.

    Published Date not suppliedChecked

  6. Primary source

    NVD CVE API 2.0 (opens a new tab)

    The NVD API page that supplied this CVE record.

    Published Date not suppliedChecked

  7. Primary source

    NVD CVE API 2.0 (opens a new tab)

    The NVD API page that supplied this CVE record.

    Published Date not suppliedChecked

  8. Primary source

    FIRST measured EPSS score (opens a new tab)

    Measured EPSS probability and percentile for CVE-2026-40863, scored 2026-10-26. This is a model estimate, not proof of exposure.

    Published Checked

Cite this record

For factual claims, cite the primary sources above; cite KEVWire for its compilation, dates, and classifications.

APA

KEVWire. (2026, October 26). PhpSpreadsheet has CPU Denial of Service via Unbounded Row Index in SpreadsheetML XML Reader (CVE-2026-40863). https://kevwire.com/record/CVE-2026-40863

MLA

"PhpSpreadsheet has CPU Denial of Service via Unbounded Row Index in SpreadsheetML XML Reader (CVE-2026-40863)." KEVWire, 26 Oct. 2026, kevwire.com/record/CVE-2026-40863.

Chicago

KEVWire. "PhpSpreadsheet has CPU Denial of Service via Unbounded Row Index in SpreadsheetML XML Reader (CVE-2026-40863)." Last modified October 26, 2026. https://kevwire.com/record/CVE-2026-40863.

Evidence summary (plain text)

PhpSpreadsheet has CPU Denial of Service via Unbounded Row Index in SpreadsheetML XML Reader (Apr 29, 2026).
The SpreadsheetML XML reader (`Reader\Xml`) does not validate the `ss:Index` row attribute against the maximum allowed row count (`AddressRange::MAX_ROW = 1,048,576`). An attacker can craft a SpreadsheetML XML file with `ss:Index="999999999"` on a ` ` element, which inflates the internal `cachedHighestRow` to ~1 billion. Any subsequent call to `getRowIterator()` without an explicit end row will attempt to iterate ~1 billion rows, causing CPU exhaustion and denial of service.

In `src/PhpSpreadsheet/Reader/Xml.php`, the `loadSpreadsheetFromFile` method processes ` ` elements:
CVSS 7.5 (version 3.1; evidence as of Oct 26, 2026; https://github.com/advisories/GHSA-84wq-86v6-x5j6).
EPSS 0.4% for the following 30 days, scored Oct 26, 2026 (https://api.first.org/data/v1/epss?cve=CVE-2026-40863&date=2026-10-26).
Sources:
GitHub-reviewed advisory GHSA-84wq-86v6-x5j6: https://github.com/advisories/GHSA-84wq-86v6-x5j6
GitHub public advisory API page: https://api.github.com/advisories?type=reviewed&per_page=100&sort=updated&direction=desc
NVD CVE-2026-40863: https://nvd.nist.gov/vuln/detail/CVE-2026-40863
Vendor advisory (via NVD references): https://github.com/PHPOffice/PhpSpreadsheet/security/advisories/GHSA-84wq-86v6-x5j6
NVD CVE API 2.0: https://services.nvd.nist.gov/rest/json/cves/2.0?lastModStartDate=2026-10-26T17:56:10.576Z&lastModEndDate=2026-10-26T19:25:57.867Z&resultsPerPage=500&startIndex=500
NVD CVE API 2.0: https://services.nvd.nist.gov/rest/json/cves/2.0?lastModStartDate=2026-10-26T17:21:53.012Z&lastModEndDate=2026-10-26T18:55:55.651Z&resultsPerPage=500&startIndex=500
NVD CVE API 2.0: https://services.nvd.nist.gov/rest/json/cves/2.0?lastModStartDate=2026-10-26T16:51:02.326Z&lastModEndDate=2026-10-26T18:20:57.477Z&resultsPerPage=500&startIndex=500
FIRST measured EPSS score: https://api.first.org/data/v1/epss?cve=CVE-2026-40863&date=2026-10-26
Record ID: CVE-2026-40863.
Record origin: Ingested record.
AI evidence: Not assessed.
Known exploitation: Not assessed.
Zero-day status: Not assessed. KEV membership alone does not establish zero-day status.
About this data

This record was ingested from a data source. Retrieved: Oct 27, 2026, 01:40 UTC. Ingestion is not an independent editorial investigation.

A CISA KEV listing documents known exploitation, not necessarily a zero-day; absence from the catalog does not prove a vulnerability has never been exploited.

Technology tags indicate possible relevance, not verified exposure. Confirm the affected product, version, and configuration against your own inventory; KEVWire does not scan your systems.

A personal reading checklist on this device, not verified remediation.

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