FlexPrice through 2.1.38 QuickBooks Webhook Signature Verification Bypass

FlexPrice through 2.1.38 contains an authentication bypass vulnerability in HandleQuickBooksWebhook that skips signature verification when the intuit-signature header is omitted. Unauthenticated attackers knowing a tenant and environment ID can replay forged payment notifications to repeatedly add payment amounts, marking invoices paid or overpaid.