Prevents CSV Formula Injection

Available since version 9.1.0

The EscapeFormula Formatter formats CSV records to reduce CSV Formula Injection in imported Spreadsheet programs.

Since version 9.7.4 the default values from the class constructor were updated to comply with the latest recommendations from OWASP regarding CSV injection. As this is a security fix, the BC break should be minimal.

Usage with CSV objects

The EscapeFormula class uses the formatter capabilities of the Writer object to escape formula injection.

public function __construct(string $escape = "'", array $special_chars = [])
public function escapeRecord(array $record): array
public function unescapeRecord(array $record): array

EscapeFormula::unescapeRecord is available since version 9.11.0

The EscapeFormula::__construct method takes two (2) arguments:

use League\Csv\EscapeFormula;
use League\Csv\Writer;

$formatter = new EscapeFormula();
$writer = Writer::createFromPath('php://temp', 'r+');
$writer->insertOne(['2', '2017-07-25', 'Important Client', '=2+5', 240, null]);
//outputting a CSV Document with all CSV Formula Injection escaped
//"2,2017-07-25,\"Important Client\",\"\t=2+5\",240,\n"

Conversely, if you obtain a CSV document containing escaped formula field you can use the Esca[eFormula::unescapeRecord to remove any escaping character.

use League\Csv\EscapeFormula;
use League\Csv\Reader;

$formatter = new EscapeFormula();
$reader = Reader::createFromPath('/path/to/my/file.csv');
// returns ['2', '2017-07-25', 'Important Client', '=2+5', '240', '']
// the escaping characters are removed.

Usage with PHP stream resources

You can use the EscapeFormula to format your records before calling fputcsv or SplFileObject::fputcsv.

use League\Csv\EscapeFormula;

$resource = fopen('/path/to/my/file', 'r+');
$formatter = new EscapeFormula("`");
foreach ($iterable_data as $record) {
    fputcsv($resource, $formatter->escapeRecord($record));

Conversely, if you have a CSV document with escaped formula, you can access the original content using the new EscapeFormula::unescapeRecord to remove any escaping character.

use League\Csv\EscapeFormula;

$resource = fopen('/path/to/my/file', 'r');
$formatter = new EscapeFormula("`");
while (($data = fgetcsv($resource)) !== false) {
    $record = $formatter->unescapeRecord($data);

Even though the EscapeFormula formatter is provided it must be stressed that this is in no way a bulletproof method. This prevention mechanism only works if you know how the CSV export will be consumed or have been generated. In any other cases, you are better off leaving the filtering to the consuming client and report any found security concerns to their respective security channel.