high CVSS 7.5

CVE-2026-40863·PHP vulnerability

PhpSpreadsheet is a pure PHP library for reading and writing spreadsheet files. Prior to 1.30.4, 2.1.16, 2.4.5, 3.10.5, and 5.7.0, 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 <Row> 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. This vulnerability is fixed in 1.30.4, 2.1.16, 2.4.5, 3.10.5, and 5.7.0.

Severity
high
Software
PHP
Fixed in
5.7.0
Published
2026-05-12

Affected versions

From: 4.0.0

Until: 5.7.0

Fixed in: 5.7.0

How to fix this CVE

Update PHP and the PhpSpreadsheet library to versions 5.7.0 or later to remediate CVE-2026-40863. This vulnerability allows attackers to craft malicious SpreadsheetML XML files that trigger excessive row iteration, leading to denial of service through CPU exhaustion. Immediate patching is recommended for production environments that process user-supplied spreadsheet files.

sudo dnf update php php-common

Defensia detects this vulnerability

How to check if you are affected

  1. Check installed PHP version: php -v
  2. Verify PhpSpreadsheet library version: grep -r 'version' vendor/phpoffice/phpspreadsheet/composer.json or check your project's composer.lock file
  3. Search application logs for repeated row iteration attempts: grep -i 'getRowIterator\|row.*999\|spreadsheet' /var/log/php-fpm.log /var/log/apache2/error.log
  4. Confirm patched version is installed: php -r "require 'vendor/autoload.php'; echo \PhpOffice\PhpSpreadsheet\Spreadsheet::VERSION;" and verify it is >= 5.7.0

FAQ

What is CVE-2026-40863?

CVE-2026-40863 is a denial-of-service vulnerability in PhpSpreadsheet's XML reader that fails to validate row index boundaries, allowing attackers to construct spreadsheet files that force iteration over billions of rows and exhaust CPU resources.

Is CVE-2026-40863 being actively exploited?

No, CVE-2026-40863 is not currently listed on the CISA Known Exploited Vulnerabilities (KEV) catalog, and no public exploits are available. However, the attack is straightforward and exploitation risk should not be underestimated.

What versions of PHP are affected by CVE-2026-40863?

The vulnerability affects PhpSpreadsheet versions 4.0.0 through 5.6.x; PHP itself is not directly vulnerable, but applications using vulnerable versions of the PhpSpreadsheet library are affected.

How do I check if my server is vulnerable to CVE-2026-40863?

Run `composer show phpoffice/phpspreadsheet` to check the installed version. If it reports a version below 5.7.0, your application is vulnerable. Also verify that your application actively processes XML spreadsheet files from untrusted sources.

Does Defensia detect CVE-2026-40863?

Yes — Defensia's CVE advisory scanner compares installed package versions against the NVD database. If PHP and PhpSpreadsheet are detected on a monitored server, CVE-2026-40863 will appear in your dashboard with remediation steps.

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References

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