CVE-2026-42570: Svelte devalue denial of service in devalue.parse

CVE-2026-42570 · Severity: high · CVSS 7.5 · Published 2026-06-09

A vulnerability in the Svelte 'devalue' library, which is used to serialize and deserialize JavaScript data, can be exploited to cause a denial-of-service (DoS) condition. By providing specially crafted data, an attacker can force the application to consume excessive amounts of memory, potentially crashing the service or making it unresponsive. This affects applications that use devalue to process untrusted user input.

Technologies: devalue (npm). Vendors: npm.

Quick answers

Is CVE-2026-42570 exploited in the wild?
No. Junglewise Threat Intelligence has no report of CVE-2026-42570 being exploited in the wild.
How severe is CVE-2026-42570?
High severity, with a CVSS score of 7.5, published 9 June 2026.
Which products and versions are affected?
devalue (npm) >= 5.6.3, <= 5.8.0, SEMVER:introduced=5.6.3,fixed=5.8.1.
Is there a fix for CVE-2026-42570?
Yes. devalue (npm): upgrade to 5.8.1 or later. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.
How is CVE-2026-42570 attacked?
It is attacked over the network, in a software library.
Am I affected by CVE-2026-42570?
Check whether you run devalue (npm) at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

How to fix

  • devalue (npm): upgrade to 5.8.1 or later
    npm install devalue@5.8.1

Technical details

The 'devalue.parse' function in Svelte's devalue library is vulnerable to a resource exhaustion issue (CWE-770). Due to specific behaviors in certain JavaScript engines, the deserialization of sparse arrays can be manipulated to allocate significantly more memory than required. An unauthenticated remote attacker can exploit this by sending a malicious payload containing a sparse array, leading to a Denial of Service (DoS) through memory exhaustion. The issue is fixed in version 5.8.1.

Affected products

  • Svelte devalue >= 5.6.3, <= 5.8.0

Identifiers

  • CVE-2026-42570
  • GHSA-77vg-94rm-hx3p

Timeline

  • 2026-05-14: disclosed
  • 2026-05-14: advisory
  • 2026-05-14: patched

References

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