validate_file( string $file, string[] $allowed_files = array() ): int

Validates a file name and path against an allowed set of rules.

Description

A return value of 1 means the file path contains directory traversal.

A return value of 2 means the file path contains a Windows drive path.

A return value of 3 means the file is not in the allowed files list.

Parameters

$filestringrequired
File path.
$allowed_filesstring[]optional
Array of allowed files.

Default:array()

Return

int 0 means nothing is wrong, greater than 0 means something was wrong.

Source

function validate_file( $file, $allowed_files = array() ) {
	if ( ! is_scalar( $file ) || '' === $file ) {
		return 0;
	}

	// `../` on its own is not allowed:
	if ( '../' === $file ) {
		return 1;
	}

	// More than one occurrence of `../` is not allowed:
	if ( preg_match_all( '#\.\./#', $file, $matches, PREG_SET_ORDER ) && ( count( $matches ) > 1 ) ) {
		return 1;
	}

	// `../` which does not occur at the end of the path is not allowed:
	if ( str_contains( $file, '../' ) && '../' !== mb_substr( $file, -3, 3 ) ) {
		return 1;
	}

	// Files not in the allowed file list are not allowed:
	if ( ! empty( $allowed_files ) && ! in_array( $file, $allowed_files, true ) ) {
		return 3;
	}

	// Absolute Windows drive paths are not allowed:
	if ( ':' === substr( $file, 1, 1 ) ) {
		return 2;
	}

	return 0;
}

Changelog

VersionDescription
1.2.0Introduced.

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