Quick answers
- Is This vulnerability exploited in the wild?
- No. Junglewise Threat Intelligence has no report of This vulnerability being exploited in the wild.
- How severe is This vulnerability?
- Medium severity, with a CVSS score of 4.7, published 21 October 2026.
- Which products and versions are affected?
- @sveltejs/kit (npm) < 3.0.0, SEMVER:introduced=0; SvelteKit before 3.0.0.
- Is there a fix for This vulnerability?
- Yes: fixed in 3.0.0. Until then: Reject requests whose parsed URL pathname begins with // before route resolution (e.g., in a reverse proxy or SvelteKit handle hook). Alternatively, disable navigation for non-redirect enhanced form results by supplying a custom submission callback that sets navigate: false.</anigation> <parameter name="timeline">[{"kind":"disclosed", "at":"2026-10-05"}, {"kind":"patched", "at":"2026-10-21"}] Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.
- How is This vulnerability attacked?
- It is attacked over the network.
- Am I affected?
- Check whether you run @sveltejs/kit (npm) or SvelteKit at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.
How to fix
- Fixed in: 3.0.0
Reject requests whose parsed URL pathname begins with // before route resolution (e.g., in a reverse proxy or SvelteKit handle hook). Alternatively, disable navigation for non-redirect enhanced form results by supplying a custom submission callback that sets navigate: false.</anigation> <parameter name="timeline">[{"kind":"disclosed", "at":"2026-10-05"}, {"kind":"patched", "at":"2026-10-21"}]
Technical details
The vulnerability exists in SvelteKit's enhanced form action handling on routes accepting paths beginning with double slashes (//). Attackers can craft action paths starting with // that become protocol-relative URLs, causing non-redirect form results to navigate victims to attacker-controlled sites. This requires user interaction (form submission) and affects versions before 3.0.0.
Affected products
- Svelte SvelteKit before 3.0.0