SvelteKit : XSS via untrusted cache-control header in prerendered page

Exploitation

No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.

CVSS

0.0 · CVSS:3.1/AV:N/AC:H/PR:H/UI:N/S:U/C:N/I:N/A:N

EPSS

• CVE-2026-114061: 0.21% estimated exploitation activity in the next 30 days; percentile 11.60 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.

As published by the source; long descriptions are shortened.

Impact Applications that prerender pages and use setHeaders to set a cache-control header from an untrusted source are vulnerable to cross-site scripting (XSS). SvelteKit inserts the header value into a <meta http-equiv="cache-control" tag without escaping it. An attacker who can influence this value at prerender time can break out of the content attribute and inject HTML or JavaScript into the generated page. The injected code can then execute when users visit the page. Patches The fix escapes the header value before inserting it into the generated HTML. Upgrade to @sveltejs/kit version 3.0.0 or later. Workarounds Avoid forwarding untrusted cache-control header values with setHeaders on prerendered pages. Use a fixed, trusted cache policy instead.

Published by the source

23 Oct 2026, 20:43 UTC

Last modified by the source

23 Oct 2026, 21:00 UTC

Source last checked

26 Oct 2026, 13:07 UTC

1. Revision 3 · amended · 26 Oct 2026

   Amended from ghsa record GHSA-27mw-82g8-phjj

2. Revision 2 · amended · 24 Oct 2026

   Amended from osv record GHSA-27mw-82g8-phjj

3. Revision 1 · created · 23 Oct 2026

   Published from ghsa record GHSA-27mw-82g8-phjj

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# Patch Next advisory brief: CVE-2026-114061

Advisory: SvelteKit : XSS via untrusted cache-control header in prerendered page
IDs: CVE-2026-114061, GHSA-27mw-82g8-phjj
Record: https://patchnext.com/advisories/cve-2026-114061 (revision 3, source checked 26 Oct 2026, 13:07 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Unrated (CVSS 0.0)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: @sveltejs/kit 3.0.0. A vendor fix does not mean a deployment is fixed.

## Affected components
- npm @sveltejs/kit: affected < 3.0.0; fixed in 3.0.0

## Suggested inspection (read-only)
- `npm ls @sveltejs/kit --all`: lists every installed copy and version, including transitive ones. Run in the project root after `npm ci`.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on @sveltejs/kit.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://github.com/advisories/GHSA-27mw-82g8-phjj (GitHub-reviewed advisory GHSA-27mw-82g8-phjj lists affected ranges: npm @sveltejs/kit >=0 <3.0.0)
- Verified: https://osv.dev/vulnerability/GHSA-27mw-82g8-phjj (OSV record GHSA-27mw-82g8-phjj lists affected ranges: npm @sveltejs/kit >=0 <3.0.0 (fixed))

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