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CVE-2026-42567 sveltejs CVE debrief

CVE-2026-42567 is a vulnerability in Svelte, 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.

Vendor
sveltejs
Product
svelte
CVSS
MEDIUM 5.9
CISA KEV
Not listed in stored evidence
Original CVE published
2026-06-09
Original CVE updated
2026-06-11
Advisory published
2026-06-09
Advisory updated
2026-06-11

Who should care

Users of Svelte framework versions between 5.51.5 and 5.55.6 should update to version 5.55.7 or later to mitigate this vulnerability.

Technical summary

The vulnerability is caused by an internal regex in the Svelte runtime that can take exponential time to test in <svelte:element this={tag}></svelte:element>. This can lead to performance issues and potential denial-of-service attacks.

Defensive priority

MEDIUM

Recommended defensive actions

  • Update Svelte to version 5.55.7 or later.
  • Review and update any affected projects that use Svelte framework versions between 5.51.5 and 5.55.6.

Evidence notes

The vulnerability is patched in version 5.55.7. For more information, see resourceLinkAnnotations with id 'ref-4' and 'ref-5'.

Sources and references

Verified primary and authoritative sources

  • CVE-2026-42567 CVE Program record

    Publisher, destination, and source semantics verified

    URL: https://www.cve.org/CVERecord?id=CVE-2026-42567

    CVE Program - Official CVE Program record with source-provided CVE metadata.

  • CVE-2026-42567 NVD vulnerability detail

    Publisher, destination, and source semantics verified

    URL: https://nvd.nist.gov/vuln/detail/CVE-2026-42567

    NIST National Vulnerability Database - Official NIST NVD detail page and source-specific vulnerability assessment.

Supplemental references

Methodology and review provenance

AI-assisted synthesis based on stored public vulnerability evidence. System validation, approval state, and publication status do not by themselves establish human review of this revision. PatchSiren helps prioritize defensive review and does not prove exposure or remediation on any system.