Socket.IO: Prototype Pollution via Unsafe Client Session Lookup

Why it is Amber

• CVSS 7.5 high
• Remotely exploitable without logging in
• On your watchlist: npm

Affected packages

References

• https://github.com/advisories/GHSA-wfpm-5gcm-94cg
• 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/releases/tag/@socket.io/cluster-engine@0.1.1
• https://github.com/advisories/GHSA-wfpm-5gcm-94cg

Original 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.