TI-2026-85241 Aliases CVE-2026-76893

tsParticles MCP server lets one anonymous session block new clients

HIGH 70CWE-400Published 2026-11-04 · Updated 2026-11-05

Key facts

Attack vector: Network
Privileges required: None
User interaction: None
Attack complexity: Low
Attack requirements: None
Impact type: Denial of service
Confidentiality · integrity · availability: None · None · Low
Fix status: Fixed

Attack profile from CVSS 4.0 · CNA. Fix status from CNA. Impact type from CWE-400.

Summary

The @tsparticles/mcp-server package in tsParticles, before 4.3.2, reuses one stateful StreamableHTTPServerTransport for every client in HTTP mode. An unauthenticated client that sends the first initialize request without an mcp-session-id claims the shared state, so later clients receive "Server already initialized" and cannot start sessions until the process restarts (CWE-400). CISA SSVC lists exploitation as proof of concept.

Written with Claude Haiku 5.5 from the sources below · 2026-11-06

Description from the CNA

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.

Why it matters now

Exploitation Proof of concept CISA SSVC · not in CISA KEV

EPSS 0.00291 21st percentileScored 2026-11-07

Fix Fixed tsparticles (tsparticles): 4.3.2mcp-server (@tsparticles): 4.3.2

SSVC decision points

CISA ADP · SSVC 2.0.3

Exploitation: Poc
Automatable: Yes
Technical impact: Partial

The decision (Track, Attend, Act) also depends on your mission and well-being impact; see CISA's SSVC guide.

Affected products

Vendor	Product	Affected versions	Fixed in	Status	Source
tsparticles	tsparticles	before 4.3.2	4.3.2	Patch available	CNA
tsparticles	mcp-server	before 4.3.2	4.3.2	Patch available	CNA

tsparticles Vendortsparticles Affected before 4.3.2 Fixed in 4.3.2 Patch available CNA
mcp-server Vendortsparticles Affected before 4.3.2 Fixed in 4.3.2 Patch available CNA

Remediation

Update tsparticles and @tsparticles/mcp-server to version 4.3.2.

Written with Claude Haiku 5.5 from the sources below · 2026-11-06

Fix · CNA tsparticles (tsparticles) Fixed in 4.3.2
Fix · CNA mcp-server (@tsparticles) Fixed in 4.3.2

Timeline

2026-11-04 Threatist record created from CVE-2026-76893
2026-11-05 CISA SSVC decision points changed
2026-11-05 Priority changed: MEDIUM → HIGH

References

Other 3

TI-2026-85246 Malformed JSON requests crash the tsParticles MCP server HTTP process CVSS 4.0HIGH 8.7
TI-2026-85240 Unbounded request body buffering in tsParticles MCP server CVSS 3.1HIGH 7.5
TI-2026-85245 Command injection in tsParticles stable publish workflow via release notes CVSS 4.0HIGH 7.5

Sources

This product uses the NVD API but is not endorsed or certified by the NVD. Sources and licences