CVE-2026-25536: MCP TypeScript SDK Cross-Client Data Leak
CVE-2026-25536 is a high-severity information disclosure issue in @modelcontextprotocol/sdk, a MCP server. Affected: >=1.10.0 <1.26.0. Fixed in 1.26.0.
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Key facts
- ID
CVE-2026-25536- Severity
- high
- Attack type
- Information disclosure
- Component
- @modelcontextprotocol/sdk · MCP server
- Package
@modelcontextprotocol/sdk- Known exploited
- No known exploitation
- Published
- Last verified
What is CVE-2026-25536?
When a single McpServer instance using StreamableHTTPServerTransport was reused across multiple HTTP clients, a common stateless deployment pattern, response routing could misfire and deliver one client's data to a different client entirely. Affected MCP SDK versions 1.10.0–1.25.3; fixed in 1.26.0. At disclosure, 82% of surveyed production MCP servers were running a vulnerable version.
Affected versions
| Affected | Fixed in |
|---|---|
>=1.10.0 <1.26.0 | 1.26.0 |
Am I affected by CVE-2026-25536?
You are affected if you run @modelcontextprotocol/sdk >=1.10.0 <1.26.0. Versions 1.26.0 and later include the fix.
How do I fix CVE-2026-25536?
Upgrade @modelcontextprotocol/sdk to 1.26.0+. If upgrading is not immediate, deploy one McpServer instance per HTTP client (no shared instances). Audit MCP server logs for cross-client response anomalies.
How do I find every machine running @modelcontextprotocol/sdk?
Anomity inventories the AI agents, MCP servers, IDE extensions and skills on each developer device, so you can see which machines run @modelcontextprotocol/sdk and which version, then enforce a policy on it.