SvelteKit before version 3.0.0 contains a server‑side request forgery flaw that can expose internal services. The framework’s self‑fetch fallback logic automatically follows HTTP redirects issued by the target of a fallback request. An attacker can set the Host or X‑Forwarded‑Host header so the fallback contact is a malicious server that issues a redirect to an internal resource. The redirect is then automatically followed by SvelteKit, allowing the attacker to retrieve data from hosts that should only be reachable from within the network. This flaw is identified as CWE‑918.

The vulnerability is present in all releases of SvelteKit before 3.0.0. Any application that uses the SvelteKit framework for server‑side rendering and has not been upgraded to 3.0.0 or later is affected. This includes deployments that rely on the default self‑fetch fallback and do not restrict the origin of redirects. The product is SvelteJS’s SvelteKit framework.

The CVSS score of 6.9 indicates moderate severity, and the EPSS score of less than 1 % suggests low current exploitation probability. The vulnerability has not been indexed in the CISA KEV catalog. Attackers can exploit the flaw remotely by sending crafted requests to an exposed endpoint that triggers the self‑fetch logic, and by manipulating headers to cause a redirect to an internal resource. While the attack requires network reachability to the application, no local privilege escalation is required; the impact, however, can be significant if sensitive internal endpoints are exposed.