PhpSpreadsheet: XmlScanner Bypass via ISO-2022 Escape Sequences Allows XXE and Denial of Service

Summary PhpSpreadsheet's XmlScanner::scan uses a regex pattern that only accounts for NULL byte 0x00 interleaving when detecting !DOCTYPE. ISO-2022 escape sequences 0x1B bytes inserted between the characters of the pattern break the regex match entirely, allowing DOCTYPE declarations with entity...