CVE-2026-25536 @modelcontextprotocol/sdk has cross-client data leak via shared server/transport instance reuse
Attackers can read other clients' data when a single server instance is reused across multiple connections in stateless deployments.
- Exploited in the wild
- Not known
- Login needed
- Any signed-in user
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-25536?
CVE-2026-25536 is a high-severity vulnerability in modelcontextprotocol typescript-sdk, published on 4 Feb 2026. Any signed-in user can exploit it over the network, with no action from the victim.
Official description
MCP TypeScript SDK is the official TypeScript SDK for Model Context Protocol servers and clients. From version 1.10.0 to 1.25.3, cross-client response data leak when a single McpServer/Server and transport instance is reused across multiple client connections, most commonly in stateless StreamableHTTPServerTransport deployments. This issue has been patched in version 1.26.0.
Which versions are affected by CVE-2026-25536?
2 open source packages ship an affected version, including @modelcontextprotocol/sdk. It affects 1 product.
| Package | Affected | Fixed in |
|---|---|---|
@modelcontextprotocol/sdk npm | From 1.10.0 | 1.26.0 |
@modelcontextprotocol/sdk npm | From 1.10.0 | 1.26.0 |
Products include Lfprojects Mcp Typescript Sdk.
How do I fix CVE-2026-25536?
Upgrade @modelcontextprotocol/sdk to 1.26.0 or later.
Is CVE-2026-25536 being exploited?
There is no known exploitation of CVE-2026-25536 in the wild and no public exploit code.
Other vulnerabilities in modelcontextprotocol typescript-sdk
Sources
Also known as CLSA-2026-1788167244, CLSA-2026-1790611463, ECHO-75cb-c27c-38de, GHSA-345p-7cg4-v4c7, MINI-2ppw-q4cq-95fx, MINI-3444-738h-p3h9 and 6 more.