CVE-2026-59933: PHPOffice PhpSpreadsheet denial of service in OLE reader

CVE-2026-59933 · Severity: high · CVSS 7.5 · Published 2026-07-28

PhpSpreadsheet is a widely used library for reading and writing spreadsheet files in PHP applications. A vulnerability in how the library processes older Excel (XLS) files allows an attacker to upload a specially crafted, tiny file that causes the server to enter an infinite loop and exhaust all available memory. This can lead to a complete service outage for any application that automatically processes or detects uploaded spreadsheet types.

Technologies: phpoffice/phpspreadsheet (Packagist), Phpoffice Phpspreadsheet. Vendors: Packagist, Phpoffice.

Quick answers

Is CVE-2026-59933 exploited in the wild?
No. Junglewise Threat Intelligence has no report of CVE-2026-59933 being exploited in the wild.
How severe is CVE-2026-59933?
High severity, with a CVSS score of 7.5, published 28 July 2026.
Which products and versions are affected?
phpoffice/phpspreadsheet (Packagist) ECOSYSTEM:introduced=4.0.0,fixed=5.8.1; Phpoffice Phpspreadsheet < 1.30.6, 2.0.0 to 2.1.17, 2.2.0 to 2.4.6, 3.3.0 to 3.10.6, 4.0.0 to 5.8.0, <= 1.30.5, >= 2.0.0 <= 2.1.17, >= 2.2.0 <= 2.4.6, >= 3.3.0 <= 3.10.6, >= 4.0.0 <= 5.8.0.
Is there a fix for CVE-2026-59933?
Yes. phpoffice/phpspreadsheet (Packagist): upgrade to 5.8.1 or later. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.
How is CVE-2026-59933 attacked?
It is attacked over the network, in a software library.
Am I affected by CVE-2026-59933?
Check whether you run phpoffice/phpspreadsheet (Packagist) or Phpoffice Phpspreadsheet at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

How to fix

  • phpoffice/phpspreadsheet (Packagist): upgrade to 5.8.1 or later
    composer require phpoffice/phpspreadsheet:^5.8.1

Technical details

An uncontrolled resource consumption vulnerability (CWE-400) exists in the OLE reader component of PhpSpreadsheet. The OLERead::read() function follows sector chains in XLS/OLE metadata without validating for cycles or enforcing a maximum chain length. An attacker can provide a malformed file where a small-block depot sector chain points back to itself, causing an infinite loop that repeatedly appends data until the PHP process exhausts its memory limit. This is reachable via automatic file type detection (Reader\Xls::canRead()), meaning even simple file uploads intended for validation can trigger the crash. The issue is fixed in versions 5.8.1, 3.10.7, 2.4.7, 2.1.18, and 1.30.6.

Affected products

  • PHPOffice PhpSpreadsheet < 1.30.6, 2.0.0 to 2.1.17, 2.2.0 to 2.4.6, 3.3.0 to 3.10.6, 4.0.0 to 5.8.0

Identifiers

  • CVE-2026-59933
  • GHSA-xh5m-36r6-47m3

Timeline

  • 2026-07-11: patched: Fix committed to repository
  • 2026-07-28: advisory: Security advisory published by GitHub and NVD

References

This page as Markdown. Free to reuse under CC BY 4.0 with a link back.