CVE-2026-76893: tsParticles: A single anonymous MCP session can monopolize HTTP mode and deny new clients
tsParticles is a TypeScript library for creating highly customizable particle animations. Prior to 4.3.2, the HTTP mode of @tsparticles/mcp-server reuses one stateful StreamableHTTPServerTransport for every client. An unauthenticated client that sends the first initialize request without an mcp-session-id claims the shared transport state, causing later independent clients to receive Server already initialized and preventing them from establishing sessions until the process restarts. The first client's session remains functional. This issue is fixed in version 4.3.2.
Remediation
Recommended actions to resolve this vulnerability, in priority order.
- Upgrade
Upgrade
@tsparticles/mcp-serverto a version that resolves this vulnerability.Fixed in 4.3.2
Event History
Frequently Asked Questions
Which deployments are exposed to this denial of service?
Deployments using the HTTP mode of @tsparticles/mcp-server before version 4.3.2 are affected. The issue concerns a process that reuses one stateful StreamableHTTPServerTransport across clients.
What does an attacker need to do to trigger the issue?
An unauthenticated client only needs to send the first initialize request without an mcp-session-id. No privileges or user interaction are required.
What is the operational impact after exploitation?
The first client retains a functional session, while later independent clients receive "Server already initialized" and cannot establish sessions. Service for new clients remains unavailable until the process is restarted.
What should be done if an update cannot be applied immediately?
Restarting the affected process restores the ability for new clients to establish sessions, but does not prevent the issue from recurring. The provided fix is version 4.3.2.