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

April 29, 2026 (updated May 13, 2026)

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.

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Code Behaviors & Features

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