Socket.IO: Prototype Pollution via Unsafe Client Session Lookup
Published Sep 29, 2026 · Updated Nov 3, 2026
Original summary
Normalized public record · Updated Nov 3, 2026
Socket.IO: Prototype Pollution via Unsafe Client Session Lookup
Publisher and source text is retained separately from QFinch interpretation.
QFinch assessment
This is a **prototype pollution / improper client lookup** vulnerability in `@socket.io/cluster-engine`.
Potential 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
Evidence: public source recordsAffected products
| Affected package, product or range | Fix status |
|---|---|
| Consult the referenced vendor advisory for affected versions. | Consult source advisory |
Matching a version is only one part of assessing exposure. QFinch has not assessed your environment on this public page.
Remediation
Apply the vendor-supported fixed release or mitigation, then verify the affected component is no longer reachable.
- Confirm the affected product and reachable code path exist in your environment.
- Apply the vendor-supported patch or mitigation from the primary advisory.
- Rescan the exact deployed revision and retain verification evidence.
Evidence coverage
- SSVC priority
- MEDIUM
- Confidence
- Not available
- Aliases
- None reported
Scores appear only when corresponding evidence exists. Missing data is never interpreted as zero risk.
Sources and record history
Record history
Published Sep 29, 2026 · Last refreshed Nov 3, 2026