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CVE-2026-42570 sveltejs CVE debrief

CVE-2026-42570 is a HIGH severity vulnerability in Svelte devalue, a JavaScript library for serializing values into strings. Versions from 5.6.3 to before 5.8.1 are vulnerable to excessive memory consumption due to quirks in some JavaScript engines when deserializing sparse arrays. This issue has been patched in version 5.8.1.

Vendor
sveltejs
Product
devalue
CVSS
HIGH 7.5
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

Developers and users of Svelte devalue versions between 5.6.3 and 5.8.1 should be aware of this vulnerability and take steps to upgrade to a patched version.

Technical summary

The vulnerability exists in the devalue.parse function, which can allocate excessive memory when deserializing sparse arrays. This can lead to high memory consumption, potentially causing performance issues or crashes.

Defensive priority

HIGH

Recommended defensive actions

  • Upgrade to Svelte devalue version 5.8.1 or later.
  • Review and update affected applications to use the patched version.

Evidence notes

The vulnerability was patched in version 5.8.1. References: [ref-4: Patch](https://github.com/sveltejs/devalue/commit/206ca6712fbc380a4571c59de9ab04b91110792d), [ref-5: Product, Release Notes](https://github.com/sveltejs/devalue/releases/tag/v5.8.1), [ref-6: Vendor Advisory](https://github.com/sveltejs/devalue/security/advisories/GHSA-77vg-94rm-hx3p).

Official resources

CVE-2026-42570 was published on 2026-06-09T17:17:07.253Z and modified on 2026-06-11T18:52:51.173Z.