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

Severity: high (CVSS 7.5 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.5% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2026-06-09 · updated 2026-07-23
Weakness: CWE-1333

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.

Affected products

sveltejs svelte: from 5.51.5 before 5.55.7 — fixed in 5.55.7

How to fix

Upgrade to a fixed version: sveltejs svelte 5.55.7. Check the vendor advisory for mitigations.

References

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

Get alerted when CVE-2026-42567 or the next vulnerability affects your stack