CVE-2026-52870 MCP Python SDK: Experimental task handlers allow any client to access and cancel other clients' tasks
Attackers can access and cancel other clients' tasks in MCP Python SDK when experimental task handlers are enabled.
- 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-2026-52870?
CVE-2026-52870 is a high-severity missing authorization vulnerability in modelcontextprotocol python-sdk, published on 15 Jul 2026. Any signed-in user can exploit it over the network, with no action from the victim.
Official description
The MCP Python SDK, called mcp on PyPI, is a Python implementation of the Model Context Protocol (MCP). From 1.23.0 until 1.27.2, default handlers installed by server.experimental.enable_tasks() for tasks/list, tasks/get, tasks/result, and tasks/cancel operate only on task identifiers without recording the session that created each task, allowing any connected client to enumerate, read results from, consume messages for, or cancel other clients' tasks. This issue is fixed in version 1.27.2.
Weakness: CWE-862
Which versions are affected by CVE-2026-52870?
3 open source packages ship an affected version, including mcp. It affects 1 product.
| Package | Affected | Fixed in |
|---|---|---|
mcp PyPI | From 1.23.0 | 1.27.2 |
mcp PyPI | From 1.23.0 | 1.27.2 |
mcp PyPI | From 1.23.0 | 1.27.2 |
Products include Lfprojects Mcp Python Sdk.
How do I fix CVE-2026-52870?
Upgrade mcp to 1.27.2 or later.
Upgrade, and check permissions on every request on the server, not only in the interface. More about Missing authorization.
Is CVE-2026-52870 being exploited?
There is no known exploitation of CVE-2026-52870 in the wild and no public exploit code.
Other vulnerabilities in modelcontextprotocol python-sdk
- CVE-2026-59950 MCP Python SDK: WebSocket server transport does not support Host/Origin validation
- CVE-2025-66416 DNS Rebinding Protection Disabled by Default in Model Context Protocol Python SDK for Servers Running on Localhost
- CVE-2026-52869 MCP Python SDK: HTTP transports serve session requests without verifying the authenticated principal
Sources
Also known as ECHO-686f-4b2a-3dd3, GHSA-hvrp-rf83-w775, MINI-2p5p-6fph-q54f, MINI-2vqf-fvc7-2m6g, MINI-66cj-vvx7-mrpc, MINI-7p24-89h3-vqc8 and 14 more.