CVE-2026-27122 Svelte SSR does not validate dynamic element tag names in `<svelte:element>`
An attacker can inject malicious HTML into server-side rendered output via unsanitized dynamic element tags in Svelte, potentially leading to XSS.
- Exploited in the wild
- Not known
- Login needed
- An administrator
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-27122?
CVE-2026-27122 is a medium-severity cross-site scripting vulnerability in sveltejs svelte, published on 20 Feb 2026. An attacker needs administrator access to exploit it, with no action from the victim.
Official description
svelte performance oriented web framework. Prior to 5.51.5, 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. This vulnerability is fixed in 5.51.5.
Weakness: CWE-79
Which versions are affected by CVE-2026-27122?
2 open source packages ship an affected version, including svelte. It affects 1 product.
| Package | Affected | Fixed in |
|---|---|---|
svelte npm | All versions | 5.51.5 |
svelte npm | All versions | 5.51.5 |
Products include Svelte Svelte.
How do I fix CVE-2026-27122?
Upgrade svelte to 5.51.5 or later.
Escape output for the context it lands in and set a strict Content Security Policy. Upgrading the affected component is the real fix. More about Cross-site scripting.
Is CVE-2026-27122 being exploited?
There is no known exploitation of CVE-2026-27122 in the wild and no public exploit code.
Other vulnerabilities in sveltejs svelte
- CVE-2021-29261 Code injection in n/a
- CVE-2026-42567 Svelte: ReDoS in `<svelte:element>` Tag Validation
- CVE-2024-45047 Potential mXSS vulnerability due to improper HTML escaping in svelte
- CVE-2022-25875 Cross-site Scripting (XSS)
- CVE-2026-42573 Svelte: XSS via DOM Clobbering of Internal Framework State
Sources
Also known as GHSA-m56q-vw4c-c2cp.