Source Defense

Source Defense protects the part of a web application that most security stacks don’t reach: the browser itself, once third-party JavaScript — analytics tags, chat widgets, payment scripts, ad tech — starts executing on a page. Network and server-side defenses can’t see what a compromised or malicious third-party script does once it runs client-side, which is exactly the mechanism behind Magecart-style digital skimming and formjacking attacks that steal payment and personal data directly out of checkout and login forms. Source Defense’s platform monitors and sandboxes that third-party script behavior in real time, aiming to prevent unauthorized data access at the point where the data is actually entered, rather than after it has already left the browser.

Founded in 2014 and headquartered in Rosh HaAyin, Israel, Source Defense has raised roughly $47.5 million to date, including a $27 million Series B led by Springtide Ventures in 2022. The company markets itself as the category creator in client-side web security and reports protecting more than 1,000 brands and roughly 1.2 billion monthly page views, with PCI DSS 4.0.1 compliance — which now explicitly requires script-level monitoring and integrity validation for payment pages — as a significant tailwind for adoption. The company has also disclosed a partnership relationship with Mastercard.

The client-side/digital supply chain risk category Source Defense pioneered has become more mainstream as PCI DSS 4.0.1 requirements phase in, which is a genuine regulatory tailwind rather than a marketing narrative. That said, most of the company’s public proof points (customer counts, page-view volume) are self-reported rather than independently audited, so buyers evaluating the platform should ask for named reference customers and specific incident-prevention data rather than relying on aggregate marketing statistics.