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High, CVSS 7.5amended

Socket.IO: Prototype Pollution via Unsafe Client Session Lookup

CVE-2026-102600GHSA-wfpm-5gcm-94cg

What to do

Vendor fix available. Upgrade each affected package to the fixed version on its release line (@socket.io/cluster-engine 0.1.1), 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

Sources

Severity and exploitation
Exploitation
No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.
CVSS
7.5 · CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
EPSS
  • CVE-2026-102600: 0.38% estimated exploitation activity in the next 30 days; percentile 32.27 (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 This is a prototype pollution / improper client lookup vulnerability in @socket.io/cluster-engine. Servers using @socket.io/cluster-engine may be impacted when attacker-controlled session IDs are processed in clustered deployments. A malicious client could use special property names such as proto, constructor, or other inherited object keys as a session identifier, causing the server to read properties from the object prototype chain instead of only real connected clients. The impact is denial of service through process crash. Applications not using @socket.io/cluster-engine are not affected by this specific issue. Affected versions: @socket.io/cluster-engine@0.1.0 Patches The issue was fixed in: @socket.io/cluster-engine@0.1.1 Workarounds If upgrading immediately is not possible, users can reduce exposure by: - Rejecting or sanitizing suspicious session IDs before they reach the cluster engine. - Running the cluster engine behind trusted infrastructure that prevents arbitrary…

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

    Amended from ghsa record GHSA-wfpm-5gcm-94cg

  2. Revision 2 · amended ·

    Amended from osv record GHSA-wfpm-5gcm-94cg

  3. Revision 1 · created ·

    Published from ghsa record GHSA-wfpm-5gcm-94cg

Agent brief

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# Patch Next advisory brief: CVE-2026-102600

Advisory: Socket.IO: Prototype Pollution via Unsafe Client Session Lookup
IDs: CVE-2026-102600, GHSA-wfpm-5gcm-94cg
Record: https://patchnext.com/advisories/cve-2026-102600 (revision 3, source checked 26 Oct 2026, 13:06 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: High (CVSS 7.5)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: @socket.io/cluster-engine 0.1.1. A vendor fix does not mean a deployment is fixed.

## Affected components
- npm @socket.io/cluster-engine: affected < 0.1.1; fixed in 0.1.1

## Suggested inspection (read-only)
- `npm ls @socket.io/cluster-engine --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 @socket.io/cluster-engine.
- 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://github.com/advisories/GHSA-wfpm-5gcm-94cg (GitHub-reviewed advisory GHSA-wfpm-5gcm-94cg lists affected ranges: npm @socket.io/cluster-engine >=0 <0.1.1)
- Verified: https://osv.dev/vulnerability/GHSA-wfpm-5gcm-94cg (OSV record GHSA-wfpm-5gcm-94cg lists affected ranges: npm @socket.io/cluster-engine >=0 <0.1.1 (fixed))

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