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Medium, CVSS 6.9amended

tsParticles: A single anonymous MCP session can monopolize HTTP mode and deny new clients

CVE-2026-76893GHSA-h7c4-q426-7jh9

What to do

Vendor fix available. Upgrade each affected package to the fixed version on its release line (@tsparticles/mcp-server 4.3.2), redeploy, then verify what is actually installed.

This page has no inventory attached, so it cannot say whether you are affected. A vendor fix is not proof that your deployment is fixed.

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Affected packages

Sources

Severity and exploitation
Exploitation
No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.
CVSS 4.0
6.9 · CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:L/SC:N/SI:N/SA:N · score source
EPSS
  • CVE-2026-76893: 0.29% estimated exploitation activity in the next 30 days; percentile 21.92 (FIRST EPSS, 2026-11-10). This is a model estimate, not proof of exploitation or customer exposure.
Source description

As published by the source; long descriptions are shortened.

Summary The HTTP mode of `@tsparticles/mcp-server` creates a single stateful `StreamableHTTPServerTransport` instance and reuses it for all clients. The first anonymous client that initializes the MCP endpoint claims the shared transport state, and later clients cannot create their own sessions. This was verified on `v4.3.0` at commit `0266d469aa2d719cb66a9c6bf09aded4186ec17c`. The same singleton transport pattern is still present in `v4.3.1` and current `main`.

Affected Code The server creates one shared transport before accepting requests: const transport = new StreamableHTTPServerTransport({ sessionIdGenerator: () => randomUUID(), }); const httpServer = createServer(async (req, res) => { ... await transport.handleRequest(req, res, parsedBody); }); Because the same transport object is reused across all requests, the first successful `initialize` call changes the state for all later clients.

Reproduction Send two independent `initialize` requests without a prior…

Dates and revisions
Published by the source
Last modified by the source
Source last checked
  1. Revision 2 · amended ·

    Amended from osv record GHSA-h7c4-q426-7jh9

  2. Revision 1 · created ·

    Published from ghsa record GHSA-h7c4-q426-7jh9

Agent brief

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# Patch Next advisory brief: CVE-2026-76893

Advisory: tsParticles: A single anonymous MCP session can monopolize HTTP mode and deny new clients
IDs: CVE-2026-76893, GHSA-h7c4-q426-7jh9
Record: https://patchnext.com/advisories/cve-2026-76893 (revision 2, source checked 10 Nov 2026, 06:25 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Medium (CVSS 6.9)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: @tsparticles/mcp-server 4.3.2. A vendor fix does not mean a deployment is fixed.

## Affected components
- npm @tsparticles/mcp-server: affected < 4.3.2; fixed in 4.3.2

## Suggested inspection (read-only)
- `npm ls @tsparticles/mcp-server --all`: lists every installed copy and version, including transitive ones. Run in the project root after `npm ci`.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on @tsparticles/mcp-server.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://github.com/advisories/GHSA-h7c4-q426-7jh9 (GitHub-reviewed advisory GHSA-h7c4-q426-7jh9 lists affected ranges: npm @tsparticles/mcp-server >=0 <4.3.2)
- Verified: https://osv.dev/vulnerability/GHSA-h7c4-q426-7jh9 (OSV record GHSA-h7c4-q426-7jh9 lists affected ranges: npm @tsparticles/mcp-server >=0 <4.3.2 (fixed))

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