CVE-2026-59933: Phpoffice Phpspreadsheet

High severity, CVSS 7.5. EPSS: 0.7% chance of exploitation in the next 30 days.

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.

Affected products

• Phpoffice Phpspreadsheet: from 4.0.0, before 5.8.1 (fixed in 5.8.1); from 3.3.0, before 3.10.7 (fixed in 3.10.7); from 2.2.0, before 2.4.7 (fixed in 2.4.7); from 2.0.0, before 2.1.18 (fixed in 2.1.18); before 1.30.6 (fixed in 1.30.6)

Published 2026-07-28. Last modified 2026-07-30.