CVE-2026-59933 — PhpSpreadsheet: XLS/OLE sector-chain self-loop causes memory exhaustion

Affected: 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 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.

GHSA-xh5m-36r6-47m3 — PHPSpreadsheet: XLS/OLE sector-chain self-loop causes memory exhaustion

Affected: Packagist: phpoffice/phpspreadsheet

## Summary

PhpSpreadsheet's 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.

## Vulnerability details

`OLERead::read()` loads the input and builds sector chains from attacker-controlled OLE header and allocation-table values:

- `src/PhpSpreadsheet/Shared/OLERead.php:82` reads the entire file after validating only the OLE magic. - `src/PhpSpreadsheet/Shared/OLERead.php:84-97` reads sector-chain metadata from the file header. - `src/PhpSpreadsheet/Shared/OLERead.php:132-146` builds `bigBlockChain` and then follows the small-block depot chain.

The vulnerable loop is:

```php $sbdBlock = $this->sbdStartBlock; $this->smallBlockChain = ''; while ($sbdBlock != -2) { $pos = ($sbdBlock + 1) * self::BIG_BLOCK_SIZE;

$this->smallBlockChain .= substr($this->data, $pos, 4 * $bbs); $pos += 4 * $bbs;

$sbdBlock = self::getInt4d($this->bigBlockChain, $sbdBlock * 4); } ```

There is no visited-sector set, no maximum iteration count, no EOF bou…

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CVE-2026-59933 — PhpSpreadsheet: XLS/OLE sector-chain self-loop causes memory exhaustion

GHSA-xh5m-36r6-47m3 — PHPSpreadsheet: XLS/OLE sector-chain self-loop causes memory exhaustion