CVE-2026-123561
Sveltejs devalue before 5.9.3 __proto__ Rejection Bypass via Property-Key Coercion
devalue before 5.9.3 allows malformed null-prototype object keys to bypass parse's __proto__ rejection through property-key coercion, an incomplete fix for GHSA-mwv9-gp5h-frr4. Attackers can supply crafted payloads that yield objects with a __proto__ own property, which alone does not cause prototype pollution.
Fixes and workarounds
Fix
devalue (npm): OSV reports a fixed version 5.9.3. Check the advisory for supported release branches.
Source: OSV GHSA-4q55-j62x-fr9hAffected products and versions
| Product | Versions | Authority |
|---|---|---|
| devalue sveltejs devalue
npm |
≥ 0; < 5.9.3 (affected, semver) 5.9.3 (unaffected, semver) Other versions: unaffected |
CNA: VulnCheck |
devaluedevalue
npm |
≥ 0; < 5.9.3 (affected, semver); OSV events: introduced 0; fixed 5.9.3Source events (semver)Other versions: unaffected |
OSV GHSA-4q55-j62x-fr9h |
Version ranges are source assertions. Check the vendor advisory and your installed configuration before determining exposure.
CVSS assessments
| Version / score | Vector | Authority |
|---|---|---|
| 4.0 / 6.3 medium |
CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:L/VA:N/SC:N/SI:N/SA:N | CNA: VulnCheck |
| 3.1 / 3.7 low |
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:L/A:N | CNA: VulnCheck |
| 4.0 / 6.3 medium |
CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:L/VA:N/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 | NVD: [email protected] |
| 3.1 / 3.7 low |
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:L/A:N | NVD: [email protected] |
Exploit evidence
No exploit evidence in collected sources. This is not proof of no exploitation.
References
- https://github.com/sveltejs/devalue/security/advisories/GHSA-4q55-j62x-fr9hCNA: VulnCheck · vendor-advisory
- https://www.vulncheck.com/advisories/sveltejs-devalue-before-5.9.3-proto-rejection-bypass-via-property-key-coercionCNA: VulnCheck · third-party-advisory
- https://github.com/sveltejs/devalue/security/advisories/GHSA-4q55-j62x-fr9h[email protected]
- https://www.vulncheck.com/advisories/sveltejs-devalue-before-5.9.3-proto-rejection-bypass-via-property-key-coercion[email protected]
- https://github.com/advisories/GHSA-4q55-j62x-fr9hOSV / GitHub Security Advisories · advisory
- https://osv.dev/vulnerability/GHSA-4q55-j62x-fr9hOSV / GitHub Security Advisories · osv
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