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

Status: published. Published: 2026-11-08. Updated: 2026-11-12.

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.

## Remediation

- fix: devalue (npm): OSV reports a fixed version 5.6.3. Check the advisory for supported release branches. (source: OSV GHSA-8qm3-746x-r74r) — https://github.com/advisories/GHSA-8qm3-746x-r74r

## Affected products and versions

- sveltejs / devalue (devalue): ≥ 0; < 5.6.3 (affected, semver); 5.6.3 (unaffected, semver). Source: CNA: VulnCheck
-  / devalue (devalue): ≥ 0; < 5.6.3 (affected, semver); OSV events: introduced 0; fixed 5.6.3. Source: OSV GHSA-8qm3-746x-r74r

## Severity and prioritization

- CVSS 4.0: 2.1 (low); 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; source: CNA: VulnCheck

- CVSS 3.1: 4.4 (medium); CVSS:3.1/AV:N/AC:H/PR:H/UI:N/S:C/C:L/I:L/A:N; source: CNA: VulnCheck

- CVSS 4.0: 2.1 (low); 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/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X; source: NVD: disclosure@vulncheck.com

- CVSS 3.1: 4.4 (medium); CVSS:3.1/AV:N/AC:H/PR:H/UI:N/S:C/C:L/I:L/A:N; source: NVD: disclosure@vulncheck.com

- CISA KEV: No listing in collected sources

- EPSS: 0.20% as of 2026-11-10; percentile 10.19%

- SSVC: exploitation none; automatable no; technical impact partial; source ADP: CISA-ADP

- Weaknesses: CWE-1321

## Exploit evidence

No exploit evidence in collected sources. This is not proof of no exploitation.

## References

- https://github.com/sveltejs/devalue/security/advisories/GHSA-8qm3-746x-r74r (CNA: VulnCheck; vendor-advisory)

- https://www.vulncheck.com/advisories/sveltejs-devalue-before-5.6.3-prototype-pollution-via-uneval-output (CNA: VulnCheck; third-party-advisory)

- https://github.com/sveltejs/devalue/security/advisories/GHSA-8qm3-746x-r74r (disclosure@vulncheck.com)

- https://www.vulncheck.com/advisories/sveltejs-devalue-before-5.6.3-prototype-pollution-via-uneval-output (disclosure@vulncheck.com)

- https://github.com/advisories/GHSA-8qm3-746x-r74r (OSV / GitHub Security Advisories; advisory)

- https://osv.dev/vulnerability/GHSA-8qm3-746x-r74r (OSV / GitHub Security Advisories; osv)

## Provenance

- CNA: VulnCheck: https://www.cve.org/CVERecord?id=CVE-2026-123568; retrieved 2026-11-12; source updated 2026-11-12

- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-123568; retrieved 2026-11-08; source updated 2026-11-08

- OSV / GitHub Security Advisories: https://osv.dev/vulnerability/GHSA-8qm3-746x-r74r; retrieved 2026-11-12; source updated 2026-11-08

- FIRST EPSS: https://api.first.org/data/v1/epss?cve=CVE-2026-123568; retrieved 2026-11-11; source updated Not reported

Revision: a885aa89c8c1a9589d963559b0581493fb13352f8cc188b33197b8526576d849

Canonical: https://y2.dev/cve/CVE-2026-123568

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