PhpWeasyPrint vulnerable to arbitrary file deletion at shutdown via public $temporaryFiles

Summary

AbstractGenerator::$temporaryFiles is a public array, and removeTemporaryFiles() — invoked from __destruct() and from a registered shutdown function — calls unlink() on every entry without verifying that the path is contained within the temporary folder. Any code holding a reference to a generator instance can push an arbitrary path into the array and have it deleted on script shutdown.

This mirrors the KnpLabs/snappy issue GHSA-87qc-37cw-84h4, patched in snappy 1.7.2.

Affected versions

pontedilana/php-weasyprint versions <= 2.5.1.

Patched in: 2.6.0.

Vulnerable code

src/AbstractGenerator.php:

public array $temporaryFiles = [];

// ...

public function removeTemporaryFiles(): void
{
    foreach ($this->temporaryFiles as $file) {
        $this->unlink($file);
    }
}

No path-containment check: whatever path is present in $temporaryFiles at shutdown is unlinked.

Proof of concept

<?php
use Pontedilana\PhpWeasyPrint\Pdf;

$pdf = new Pdf();
$pdf->temporaryFiles[] = '/var/www/html/.env';

// On shutdown, removeTemporaryFiles() deletes /var/www/html/.env.

Impact

• Arbitrary file deletion bound to script shutdown, scoped to the privileges of the PHP process user.
• Not directly exploitable on its own (the attacker already needs to influence the property in the same request). The risk is amplification: chained with a separate disclosure bug it enables leak-then-delete-to-cover-tracks, and any deserialization/property-oriented gadget that reaches this property becomes a generic file-delete primitive.

CWE-73 (External Control of File Name or Path).

Suggested fix

Only delete files that actually live inside the temporary folder, comparing canonical (realpath) paths:

public function removeTemporaryFiles(): void
{
    $temporaryFolderPath = \realpath($this->getTemporaryFolder());
    if (false === $temporaryFolderPath) {
        return;
    }
    $temporaryFolderPath = \rtrim($temporaryFolderPath, \DIRECTORY_SEPARATOR) . \DIRECTORY_SEPARATOR;

    foreach ($this->temporaryFiles as $file) {
        $filePath = \realpath($file);
        if (false === $filePath || 0 !== \strncmp($filePath, $temporaryFolderPath, \strlen($temporaryFolderPath))) {
            continue;
        }
        $this->unlink($file);
    }
}

(The trailing directory separator prevents a sibling folder such as /tmpevil from matching /tmp; strncmp is used instead of str_starts_with to keep PHP 7.4 compatibility.)

Credit

Reported upstream to KnpLabs/snappy (GHSA-87qc-37cw-84h4); identified as applicable to pontedilana/php-weasyprint, which mirrors the same code.