Key points
- CVE-2026-111767 affects @modelcontextprotocol/sdk versions 1.24.0 through 1.31.0.
- Clients sharing an InMemoryTaskStore could list, read, and cancel each other's tasks.
- The fix is available in version 1.32.0; experimental tasks are deprecated.
The Model Context Protocol (MCP) SDK for TypeScript contains a high-severity vulnerability that compromises session isolation. Versions 1.24.0 through 1.31.0 of the @modelcontextprotocol/sdk package are affected. A patch is available in version 1.32.0. The flaw allows clients to access tasks created by other sessions if they share the same task store.
In plain English
The issue stems from the experimental tasks feature, specifically the `taskStore` component. In vulnerable versions, the system did not verify which session created a specific task. This meant that if multiple clients used the same `InMemoryTaskStore`, one client could see, read, or cancel tasks belonging to another client. The vulnerability does not affect the 2.x package versions.
The background
According to the National Vulnerability Database, CVE-2026-111767 has a CVSS score of 8.6, which is rated as high severity. The weakness involves improper check for condition before action and asynchronous method execution. The GitHub advisory notes that experimental tasks are deprecated. The specification updated on July 28, 2026, replaced them with a redesigned extension.
What changes now
Version 1.32.0 ties each task to the session that created it. This ensures that a client starting a new session cannot reach earlier tasks from other sessions. If you cannot upgrade immediately, you should remove the `taskStore` or create one `InMemoryTaskStore` per session. Running a grep command for `taskstore` can help determine if your code is affected.
Who needs to act first
Teams managing public-facing servers should prioritize updating any systems using the vulnerable SDK versions. Before rolling out the patch, verify that your application does not rely on the deprecated experimental tasks feature. If the feature is in use, test the upgrade in a staging environment to ensure the new session isolation logic does not break existing workflows. Back up your configuration files before making changes. Monitor logs for any unexpected access patterns during the transition period.
What to do and how to stay safe: @modelcontextprotocol/sdk
- Check your project dependencies for @modelcontextprotocol/sdk versions between 1.24.0 and 1.31.0.
- Upgrade to version 1.32.0 or later as soon as possible to apply the session isolation fix.
- If upgrading is not immediately possible, isolate sessions by creating a separate InMemoryTaskStore for each client.
- Remove the deprecated experimental tasks feature from your codebase to align with the latest specification.
Step-by-step guide: Emergency Patching: How to Fix Critical Flaws Without Breaking Systems
General security guidance from the Patch Review newsroom. It is not confirmed advice from the organisations named in this story.
Frequently asked questions
Is the MCP SDK 2.x version affected by this vulnerability?
No, the 2.x packages are not affected by CVE-2026-111767. The issue only impacts versions 1.24.0 through 1.31.0.
How can I tell if my code is using the vulnerable feature?
You can search your codebase using `grep -ri taskstore --exclude-dir=node_modules .`. If it finds nothing, you are not affected.
What is the recommended long-term solution for experimental tasks?
The best course of action is to stop using experimental tasks, as they are deprecated and replaced by a redesigned extension in the 2026-07-28 specification.
