Socket.IO: Prototype Pollution via Unsafe Client Session Lookup (CVE-2026-102600) | HOL Guard CVE

High · CVSS 7.5CVE-2026-102600

Socket.IO: Prototype Pollution via Unsafe Client Session Lookup

Answer in brief

CVE-2026-102600 records a High severity (CVSS 7.5) vulnerability in Socket.IO: Prototype Pollution via Unsafe Client Session Lookup. The current sources do not mark it as known exploited. The current feed maps @socket.io/cluster-engine (generic), socketio/socket.io (generic). Check affected ranges and fixed versions before updating.

Analysis pending evidence review

HOL Guard separates source facts from reviewed analysis. See the methodology.

Published Sep 29, 2026Updated Sep 29, 2026Source checked Sep 29, 2026First seen by HOL Sep 29, 2026Material review Sep 29, 2026

Upstream Advisory

Key facts

Risk: High · CVSS 7.5
Exploitation: Not marked as known exploited
Affected software: 2 mapped packages or products
Fix availability: Available

Why this deserves its current priority

CVSS is 7.5. The current sources do not mark it as known exploited. Treat this as a source-backed prioritization signal, not a statement about your environment.

Analysis status

Analysis pending evidence review

Factual feed record only; HOL analysis is not approved for indexing. Read the methodology.

Affected scope and exposure questions

The current feed maps @socket.io/cluster-engine (generic), socketio/socket.io (generic). Check affected ranges and fixed versions before updating.

Mapped affected packages and fixed versions
Package	Affected range	Fixed version
@socket.io/cluster-enginegeneric	<0.1.1	0.1.1
socketio/socket.iogeneric	<0.1.1	0.1.1

Recommended response

Check inventory. Check lockfiles and deployed manifests for @socket.io/cluster-engine, socketio/socket.io.
Review the reported fix. Update @socket.io/cluster-engine to 0.1.1; socketio/socket.io to 0.1.1 if you use the affected versions. Test the change in a non-production environment first.

Evidence timeline and material changes

Published upstream
Sep 29, 2026
Evidence: source:cvelist:source_dates:source-dates:record
Source modified
Sep 29, 2026
Evidence: source:cvelist:source_dates:source-dates:record
First seen by HOL
Sep 29, 2026

Sources and claim methodology

Upstream source description

Socket.IO enables bidirectional and low-latency communication for every platform. Prior to 0.1.1, @socket.io/cluster-engine uses inherited object properties when looking up attacker-controlled session IDs in clustered deployments. Special property names such as __proto__ or constructor can resolve through the object prototype chain instead of identifying an actual connected client, causing the Node.js process to crash and resulting in denial of service. Applications that do not use @socket.io/cluster-engine are not affected. This issue is fixed in version 0.1.1.

Quoted source text, attributed separately from HOL analysis.