---
id: "CVE-2026-123568"
page: "https://infrastack.ai/live/CVE-2026-123568"
kind: "vulnerability"
aliases: ["CVE-2026-123568"]
title: "devalue: prototype pollution in uneval lets untrusted data alter object prototypes"
severity: "medium"
cvss: 4.4
epss: null
exploited: false
status: "open"
category: "package"
products: []
ecosystems: []
tags: ["javascript", "npm", "package", "svelte", "sveltekit"]
not_affected_if: ["no-uneval-usage", "trusted-data-only"]
published_at: "2026-11-08T02:16:49+00:00"
first_seen_at: "2026-11-08T02:21:12+00:00"
updated_at: "2026-11-08T02:25:34+00:00"
sources: [{"source": "nvd", "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-123568", "first_seen_at": "2026-11-08T02:21:12+00:00"}]
exploit_sources: []
---

# devalue: prototype pollution in uneval lets untrusted data alter object prototypes

Link for people: https://infrastack.ai/live/CVE-2026-123568 (this .md is for agents)

devalue, a Svelte serialization library, is vulnerable to prototype pollution when untrusted data is passed to its uneval function. When the generated code is later evaluated, objects get polluted prototypes and produce output whose shape differs from the input.

_Summary, check and fix written by a model from the sources; labelled as such._

## How to check

- Check the installed devalue version with `npm ls devalue` in each project.
- Search lockfiles for devalue entries below `5.6.3`.
- Find places where untrusted input reaches `uneval` and its output is evaluated.

## Fix

- devalue: move to `5.6.3` or later

## Timeline

- 2026-11-08T02:21:12+00:00 nvd https://nvd.nist.gov/vuln/detail/CVE-2026-123568

## Documents

- [advisory] Vendor advisory: github.com https://github.com/sveltejs/devalue/security/advisories/GHSA-8qm3-746x-r74r
- [advisory] Third-party advisory: www.vulncheck.com https://www.vulncheck.com/advisories/sveltejs-devalue-before-5.6.3-prototype-pollution-via-uneval-output

## From the sources

Sveltejs devalue before 5.6.3 contains a prototype pollution vulnerability that allows attackers to alter object prototypes by supplying untrusted data to uneval. When the generated code is later evaluated, it creates objects with polluted prototypes, producing output data whose shape differs from the original input.

---

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