# 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.

- **Severity:** High 7.1 (`CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:L/A:N`)
- **Exploited in the wild:** Not known
- **Login needed:** Any signed-in user
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 4 Feb 2026
- **Updated:** 15 Jul 2026
- **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, MINI-8v5r-f66r-m8gh, MINI-f9qj-jvj6-m9x5, MINI-p2hc-wj6f-q334, MINI-r3h5-q4h6-62pf, MINI-vq82-8qj5-2gcf, MINI-xxh7-89ff-c6mw

## 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.

Weakness: CWE-367 (Time-of-check Time-of-use (TOCTOU) Race Condition), CWE-362 (Concurrent Execution using Shared Resource with Improper Synchronization)

## Which versions are affected by CVE-2026-25536?

2 open source packages ship an affected version, including @modelcontextprotocol/sdk. It affects 1 product.


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `@modelcontextprotocol/sdk` | npm | From 1.10.0 | 1.26.0 |
| `@modelcontextprotocol/sdk` | npm | From 1.10.0 | 1.26.0 |

Products: 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

- [CVE-2026-0621](https://insights.sbomify.com/CVE-2026-0621/): MCP TypeScript SDK UriTemplate Exploded Array Pattern ReDoS (high 8.7)
- [CVE-2025-66414](https://insights.sbomify.com/CVE-2025-66414/): DNS Rebinding Protection Disabled by Default in Model Context Protocol TypeScript SDK for Servers Running on Localhost (high 7.6)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-25536 and fix it if it is affected.

What it is: 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.
Exploitation: There is no known exploitation of CVE-2026-25536 in the wild and no public exploit code.

Affected packages and fixed versions:
- @modelcontextprotocol/sdk (npm): affected from 1.10.0; fixed in 1.26.0
- @modelcontextprotocol/sdk (npm): affected from 1.10.0; fixed in 1.26.0

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-25536/ (Markdown: https://insights.sbomify.com/CVE-2026-25536/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-25536
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-25536
- OSV: https://osv.dev/vulnerability/CVE-2026-25536

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-25536/
Summaries are generated and may contain mistakes; the official description above is the record.