CVE-2026-40902: PhpSpreadsheet: CPU Denial of Service via Unbounded Row Number in XLSX Row Dimensions

Severity: high (CVSS 7.5 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.4% probability of exploitation in the next 30 days
Public exploit or detection template: yes
Published: 2026-05-12 · updated 2026-10-26
Weakness: CWE-770

Description

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 XLSX reader's ColumnAndRowAttributes::readRowAttributes() method reads row numbers from XML attributes without validating them against the spreadsheet maximum row limit (AddressRange::MAX_ROW = 1,048,576). An attacker can craft a minimal XLSX file (~1.6KB) containing a <row r="999999999"/> element that inflates cachedHighestRow to 999,999,999, causing any subsequent row iteration to attempt ~1 billion loop cycles and exhaust CPU resources. This vulnerability is fixed in 1.30.4, 2.1.16, 2.4.5, 3.10.5, and 5.7.0.

Affected products

PHPOffice PhpSpreadsheet: before 1.30.4; from 2.0.0 before 2.1.16; from 2.2.0 before 2.4.5; from 3.3.0 before 3.10.5; from 4.0.0 before 5.7.0 — fixed in 1.30.4, 2.1.16, 2.4.5, 3.10.5, 5.7.0

How to fix

Upgrade to a fixed version: PHPOffice PhpSpreadsheet 1.30.4, 2.1.16, 2.4.5, 3.10.5. Check the vendor advisory for mitigations.

References

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