Socket.IO: Prototype Pollution via Unsafe Client Session Lookup
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 clients from crafting raw Engine.IO session-related requests.
These workarounds are defense-in-depth only. Upgrading to a patched version is recommended.
Affected software
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| Platform | Package | Vulnerable versions | Fixed in |
|---|---|---|---|
| npm package | @socket.io/cluster-engine | < 0.1.1 | 0.1.1 |
References
- https://github.com/socketio/socket.io/security/advisories/GHSA-wfpm-5gcm-94cg
- https://nvd.nist.gov/vuln/detail/CVE-2026-102600
- https://github.com/socketio/socket.io/commit/830e3642ebb8dc3784eb749b0a004fe2b932b429
- https://github.com/socketio/socket.io
- https://github.com/socketio/socket.io/releases/tag/@socket.io/cluster-engine@0.1.1
- CVSS vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H- Weakness (CWE)
CWE-20- Platform
- npm
- Package
@socket.io/cluster-engine- Disclosed
- 05.10.2026
- Updated
- 11.10.2026 10:22
Sources and licenses
OSV / GitHub Advisory Database - GHSA-wfpm-5gcm-94cg - CC BY 4.0
Vulnerability history: @socket.io/cluster-engine
All published vulnerabilities of this package (npm package), newest first. Shows whether this is a one-off slip or a package that needs watching.
This is the only known vulnerability of this package.
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