# CVE-2026-123569: Devalue before 5.6.3 Denial of Service via Sparse Array Serialization

Status: published. Published: 2026-11-08. Updated: 2026-11-10.

The devalue package for npm before 5.6.3 can consume excessive CPU and memory when serializing sparse arrays with uneval or stringify. An attacker who manages to get a sparse array created on the server, which mainstream wire formats do not allow, and serialized there can cause a denial of service.

## Remediation

- fix: devalue (npm): OSV reports a fixed version 5.6.3. Check the advisory for supported release branches. (source: OSV GHSA-33hq-fvwr-56pm) — https://github.com/advisories/GHSA-33hq-fvwr-56pm

## 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-33hq-fvwr-56pm

## Severity and prioritization

- CVSS 4.0: 8.7 (high); CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N; source: CNA: VulnCheck

- CVSS 3.1: 7.5 (high); CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H; source: CNA: VulnCheck

- CVSS 4.0: 8.7 (high); CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/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: 7.5 (high); CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H; source: NVD: disclosure@vulncheck.com

- CISA KEV: No listing in collected sources

- EPSS: 0.34% as of 2026-11-10; percentile 28.13%

- SSVC: exploitation none; automatable yes; technical impact partial; source ADP: CISA-ADP

- Weaknesses: CWE-770

## Exploit evidence

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

## References

- https://github.com/sveltejs/devalue/security/advisories/GHSA-33hq-fvwr-56pm (CNA: VulnCheck; vendor-advisory)

- https://www.vulncheck.com/advisories/devalue-before-5.6.3-denial-of-service-via-sparse-array-serialization (CNA: VulnCheck; third-party-advisory)

- https://github.com/sveltejs/devalue/security/advisories/GHSA-33hq-fvwr-56pm (disclosure@vulncheck.com)

- https://www.vulncheck.com/advisories/devalue-before-5.6.3-denial-of-service-via-sparse-array-serialization (disclosure@vulncheck.com)

- https://github.com/advisories/GHSA-33hq-fvwr-56pm (OSV / GitHub Security Advisories; advisory)

- https://osv.dev/vulnerability/GHSA-33hq-fvwr-56pm (OSV / GitHub Security Advisories; osv)

## Provenance

- CNA: VulnCheck: https://www.cve.org/CVERecord?id=CVE-2026-123569; retrieved 2026-11-10; source updated 2026-11-10

- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-123569; retrieved 2026-11-08; source updated 2026-11-08

- OSV / GitHub Security Advisories: https://osv.dev/vulnerability/GHSA-33hq-fvwr-56pm; retrieved 2026-11-10; source updated 2026-11-08

- FIRST EPSS: https://api.first.org/data/v1/epss?cve=CVE-2026-123569; retrieved 2026-11-10; source updated Not reported

Revision: 097dfe3931022b59db860d74b0b8f0df6ec840ee28191c00ba45b025ff0c53ee

Canonical: https://y2.dev/cve/CVE-2026-123569

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