CVE-2026-123561 (GCVE-0-2026-123561)

Vulnerability from cvelistv5 – Published: 2026-11-08 01:38 – Updated: 2026-11-08 01:38
VLAI
Title
Sveltejs devalue before 5.9.3 __proto__ Rejection Bypass via Property-Key Coercion
Summary
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.
Severity
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
3.7 (Low)
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:L/A:N
CWE
  • CWE-1321 - Improperly Controlled Modification of Object Prototype Attributes ('Prototype Pollution')
Assigner
VulnCheck CNA
References
Impacted products
Vendor Product Version
sveltejs devalue Affected: 0 , < 5.9.3 (semver)
Unaffected: 5.9.3 (semver)
    cpe:2.3:a:svelte:devalue:*:*:*:*:*:*:*:*
Create a notification for this product.
Date Public
2026-09-18 00:00
Credits
elliott-with-the-longest-name-on-github
Show details on NVD website
To clipboard 

{
  "containers": {
    "cna": {
      "affected": [
        {
          "defaultStatus": "unaffected",
          "packageURL": "pkg:npm/devalue",
          "product": "devalue",
          "vendor": "sveltejs",
          "versions": [
            {
              "lessThan": "5.9.3",
              "status": "affected",
              "version": "0",
              "versionType": "semver"
            },
            {
              "status": "unaffected",
              "version": "5.9.3",
              "versionType": "semver"
            }
          ]
        }
      ],
      "cpeApplicability": [
        {
          "nodes": [
            {
              "cpeMatch": [
                {
                  "criteria": "cpe:2.3:a:svelte:devalue:*:*:*:*:*:*:*:*",
                  "versionEndExcluding": "5.9.3",
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                }
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              "negate": false,
              "operator": "OR"
            }
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          "type": "remediation developer",
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      ],
      "datePublic": "2026-09-18T00:00:00.000Z",
      "descriptions": [
        {
          "lang": "en",
          "value": "devalue before 5.9.3 allows malformed null-prototype object keys to bypass parse\u0027s __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."
        }
      ],
      "metrics": [
        {
          "cvssV4_0": {
            "Automatable": "NOT_DEFINED",
            "Recovery": "NOT_DEFINED",
            "Safety": "NOT_DEFINED",
            "attackComplexity": "LOW",
            "attackRequirements": "PRESENT",
            "attackVector": "NETWORK",
            "baseScore": 6.3,
            "baseSeverity": "MEDIUM",
            "exploitMaturity": "NOT_DEFINED",
            "privilegesRequired": "NONE",
            "providerUrgency": "NOT_DEFINED",
            "subAvailabilityImpact": "NONE",
            "subConfidentialityImpact": "NONE",
            "subIntegrityImpact": "NONE",
            "userInteraction": "NONE",
            "valueDensity": "NOT_DEFINED",
            "vectorString": "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",
            "version": "4.0",
            "vulnAvailabilityImpact": "NONE",
            "vulnConfidentialityImpact": "NONE",
            "vulnIntegrityImpact": "LOW",
            "vulnerabilityResponseEffort": "NOT_DEFINED"
          },
          "format": "CVSS"
        },
        {
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            "attackComplexity": "HIGH",
            "attackVector": "NETWORK",
            "availabilityImpact": "NONE",
            "baseScore": 3.7,
            "baseSeverity": "LOW",
            "confidentialityImpact": "NONE",
            "integrityImpact": "LOW",
            "privilegesRequired": "NONE",
            "scope": "UNCHANGED",
            "userInteraction": "NONE",
            "vectorString": "CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:L/A:N",
            "version": "3.1"
          },
          "format": "CVSS"
        }
      ],
      "problemTypes": [
        {
          "descriptions": [
            {
              "cweId": "CWE-1321",
              "description": "Improperly Controlled Modification of Object Prototype Attributes (\u0027Prototype Pollution\u0027)",
              "lang": "en",
              "type": "CWE"
            }
          ]
        }
      ],
      "providerMetadata": {
        "dateUpdated": "2026-11-08T01:38:01.726Z",
        "orgId": "83251b91-4cc7-4094-a5c7-464a1b83ea10",
        "shortName": "VulnCheck"
      },
      "references": [
        {
          "name": "GitHub Security Advisory (GHSA-4q55-j62x-fr9h)",
          "tags": [
            "vendor-advisory"
          ],
          "url": "https://github.com/sveltejs/devalue/security/advisories/GHSA-4q55-j62x-fr9h"
        },
        {
          "name": "VulnCheck Advisory: Sveltejs devalue before 5.9.3 __proto__ Rejection Bypass via Property-Key Coercion",
          "tags": [
            "third-party-advisory"
          ],
          "url": "https://www.vulncheck.com/advisories/sveltejs-devalue-before-5.9.3-proto-rejection-bypass-via-property-key-coercion"
        }
      ],
      "title": "Sveltejs devalue before 5.9.3 __proto__ Rejection Bypass via Property-Key Coercion",
      "x_generator": {
        "engine": "vulncheck-endgame"
      }
    }
  },
  "cveMetadata": {
    "assignerOrgId": "83251b91-4cc7-4094-a5c7-464a1b83ea10",
    "assignerShortName": "VulnCheck",
    "cveId": "CVE-2026-123561",
    "datePublished": "2026-11-08T01:38:01.726Z",
    "dateReserved": "2026-11-06T00:50:45.483Z",
    "dateUpdated": "2026-11-08T01:38:01.726Z",
    "state": "PUBLISHED"
  },
  "dataType": "CVE_RECORD",
  "dataVersion": "5.2"
}



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