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High, CVSS 8.7amended

Immutable is vulnerable to Prototype Pollution

CVE-2026-29063GHSA-wf6x-7x77-mvgw

What to do

Vendor fix available. Upgrade each affected package to the fixed version on its release line (immutable 5.1.5, 4.3.8, 3.8.3), redeploy, then verify what is actually installed.

This page has no inventory attached, so it cannot say whether you are affected. A vendor fix is not proof that your deployment is fixed.

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Affected packages

  • npm immutable

    Affected
    >= 5.0.0, < 5.1.5>= 4.0.0-rc.1, < 4.3.8< 3.8.3
    Fixed in
    5.1.5, 4.3.8, 3.8.3

Sources

Severity and exploitation
Exploitation
No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.
CVSS 4.0
8.7 · CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:N/VA:N/SC:N/SI:N/SA:N · score source
EPSS
  • CVE-2026-29063: 0.99% estimated exploitation activity in the next 30 days; percentile 62.57 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.
Source description

As published by the source; long descriptions are shortened.

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? -…

Dates and revisions
Published by the source
Last modified by the source
Source last checked
  1. Revision 3 · amended ·

    Amended from ghsa record GHSA-wf6x-7x77-mvgw

  2. Revision 2 · amended ·

    Reviewed OSV alias/range/CVSS4 correction; package source scopes and original publication preserved. No customer finding resolved.

  3. Revision 1 · created ·

    Published from osv record GHSA-wf6x-7x77-mvgw

Agent brief

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# Patch Next advisory brief: CVE-2026-29063

Advisory: Immutable is vulnerable to Prototype Pollution
IDs: CVE-2026-29063, GHSA-wf6x-7x77-mvgw
Record: https://patchnext.com/advisories/cve-2026-29063 (revision 3, source checked 26 Oct 2026, 12:50 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: High (CVSS 8.7)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: immutable 5.1.5, 4.3.8, 3.8.3. A vendor fix does not mean a deployment is fixed.

## Affected components
- npm immutable: affected >= 5.0.0, < 5.1.5; >= 4.0.0-rc.1, < 4.3.8; < 3.8.3; fixed in 5.1.5, 4.3.8, 3.8.3

## Suggested inspection (read-only)
- `npm ls immutable --all`: lists every installed copy and version, including transitive ones. Run in the project root after `npm ci`.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on immutable.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://osv.dev/vulnerability/GHSA-wf6x-7x77-mvgw (OSV record GHSA-wf6x-7x77-mvgw lists affected ranges: npm immutable >=4.0.0-rc.1 =5.0.0 =0 <3.8.3 (fixed))
- Verified: https://github.com/advisories/GHSA-wf6x-7x77-mvgw (GitHub-reviewed advisory GHSA-wf6x-7x77-mvgw lists affected ranges: npm immutable >=5.0.0 =4.0.0-rc.1 =0 <3.8.3)

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