# 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.

- **Severity:** High 7.6 (`CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:L/A:L`)
- **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:** 15 Jul 2026
- **Updated:** 16 Jul 2026
- **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, MINI-8fq3-wj4q-2qmc, MINI-c536-gg75-h86h, MINI-crj4-792v-p42j, MINI-f2vx-226h-5c7m, MINI-g965-6pcj-8442, MINI-hcqr-5752-v68j, MINI-hhvq-g349-36pj, MINI-hmh8-jxjr-994x, MINI-jh4q-f668-fp74, MINI-qc9p-5xc4-rhxp, MINI-w48m-fmjg-j2gx, MINI-wmf3-j9hv-59wf, PYSEC-2026-3481, ROOT-APP-PYPI-CVE-2026-52870

## 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 (Missing Authorization)

## Which versions are affected by CVE-2026-52870?

3 open source packages ship an affected version, including mcp. It affects 1 product.


| Package | Ecosystem | 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: Lfprojects Mcp Python Sdk.

## How do I fix CVE-2026-52870?

Upgrade mcp to 1.27.2 or later.

## 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](https://insights.sbomify.com/CVE-2026-59950/): MCP Python SDK: WebSocket server transport does not support Host/Origin validation (high 7.6)
- [CVE-2025-66416](https://insights.sbomify.com/CVE-2025-66416/): DNS Rebinding Protection Disabled by Default in Model Context Protocol Python SDK for Servers Running on Localhost (high 7.6)
- [CVE-2026-52869](https://insights.sbomify.com/CVE-2026-52869/): MCP Python SDK: HTTP transports serve session requests without verifying the authenticated principal (high 7.1)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-52870 and fix it if it is affected.

What it is: 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.
Exploitation: There is no known exploitation of CVE-2026-52870 in the wild and no public exploit code.

Affected packages and fixed versions:
- mcp (PyPI): affected from 1.23.0; fixed in 1.27.2
- mcp (PyPI): affected from 1.23.0; fixed in 1.27.2
- mcp (PyPI): affected from 1.23.0; fixed in 1.27.2

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-2026-52870/ (Markdown: https://insights.sbomify.com/CVE-2026-52870/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-52870
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-52870
- OSV: https://osv.dev/vulnerability/CVE-2026-52870

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From sbomify Insights: https://insights.sbomify.com/CVE-2026-52870/
Summaries are generated and may contain mistakes; the official description above is the record.