CVE-2026-59933 remediation guide

PHPOffice PhpSpreadsheet

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 re...

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Research in progress

A verified fixed-version field is not available. Use the linked NVD and supporting references, then confirm the vendor-supported path before changing production systems.

ProductPHPOffice PhpSpreadsheet

Affected versions>= >= 4.0.0, < 5.8.1, >= >= 3.3.0, < 3.10.7, >= >= 2.2.0, < 2.4.7, >= >= 2.0.0, < 2.1.18, >= < 1.30.6

Fixed versionsNo verified fixed-version field is available yet

Priority basisReview · CVSS 7.5 · EPSS -

Identify the affected asset

Confirm whether PHPOffice PhpSpreadsheet is installed, record the deployed version and installation path, and identify exposed interfaces.

Record the product name, package or appliance identifier, and installed version.
Identify internet-facing, administrative, API, and internal access paths.
Preserve the pre-change configuration and relevant service logs.

Validate the affected-version match

Compare the deployed version with the affected range: >= >= 4.0.0, < 5.8.1, >= >= 3.3.0, < 3.10.7, >= >= 2.2.0, < 2.4.7, >= >= 2.0.0, < 2.1.18, >= < 1.30.6. Treat incomplete inventory results as unresolved.

Prioritize with independent signals

The CVSS severity warrants an early asset and exposure review. Combine this signal with asset criticality, exposure, compensating controls, and business impact.

Apply supported remediation

Follow the vendor advisory or supported update path. Current fixed-version status: No verified fixed-version field is available yet. Preserve configuration and rollback material before change.

Verify the result

Confirm the resulting version, service health, authentication and access paths, monitoring coverage, and relevant security logs.

Confirm the expected version and package state.
Run a functional health check for critical service paths.
Review authentication, error, application, and security monitoring logs.
Reassess exposure if the supported fix cannot be applied.

Operational boundary

This page does not replace the vendor advisory, support contract, change-management process, or recovery plan. Do not infer that an asset is unaffected from an incomplete inventory query or a missing fixed-version field.