Svelte SSR does not validate dynamic element tag names in `<svelte:element>`
Date: 2026-02
Affected: npm/svelte
Attack vector: xss
Category: vulnerability-disclosure
Severity: Medium
CVE: CVE-2026-27122
CWE: CWE-79

When using `<svelte:element this={tag}>` in server-side rendering, the provided tag name is not validated or sanitized before being emitted into the HTML output. If the tag string contains unexpected characters, it can result in HTML injection in the SSR output. Client-side rendering is not affected.


Mitigations:

Architectural layers (MAESTRO):