CVE-2026-52870

MCP Python SDK: Experimental task handlers allow any client to access and cancel other clients' tasks

Published Jul 15, 2026 CVSS 3.1 · 7.6 High EPSS < 1% KEV · Not listed

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.

Analysis

Technical impact

The MCP Python SDK, known as mcp on PyPI, implements the Model Context Protocol. Between versions 1.23.0 and 1.27.2 the default handlers installed by server.experimental.enable_tasks()—specifically tasks/list, tasks/get, tasks/result, and tasks/cancel—operate only on task identifiers and do not record, and therefore do not verify, the session that created each task. As a result, any connected client can enumerate, read results from, consume messages for, or cancel tasks belonging to other clients. This missing access‑control flaw (CWE-862) enables an attacker to access or interfere with tasks they should not be authorized to manipulate. The issue is resolved in version 1.27.2.

Affected Systems

Vendors and products affected include the ModelContextProtocol Python SDK, specifically versions 1.23.0 up to and including 1.27.2. The issue is resolved in the 1.27.2 release; users of earlier releases are vulnerable.

Risk and Exploitability

The CVSS score of 7.6 indicates a high severity risk, though the EPSS score of less than 1% suggests a very low current exploitation probability. Based on the description, it is inferred that the attack vector is primarily internal: any client authorized to connect to the MCP server can exploit the flaw. The vulnerability is not listed in the CISA KEV catalog, so widespread compromise has not yet been observed, but the potential for unauthorized task interference remains significant for environments with multiple clients.

Affected Products

Default status is the baseline for the product, each version can override it (e.g. patched versions marked unaffected).

Vendor Product Default status Versions

modelcontextprotocol

python-sdk

affected

Version	Status	Constraints
`>= 1.23.0, < 1.27.2`	affected	—

Configuration 1 [-]

cpe:2.3:a:lfprojects:mcp_python_sdk:*:*:*:*:*:*:*:*

No data.

Vendor Product Versions

Modelcontextprotocol

Python-sdk

Version	Status	Scheme	Platform
`[1.23.0,1.27.2)`	affected	semver	—

Remediation

No solution or workaround provided in the CVE record.

OpenCVE Recommended Actions

Upgrade the Python SDK to version 1.27.2 or later, where the bug has been fixed to record the session for task handlers.
If an upgrade is not immediately possible, disable the experimental task feature by removing or commenting out the server.experimental.enable_tasks() invocation so the vulnerable handlers are not activated.
Restrict network access to the MCP server by configuring firewall rules or network segmentation to allow only trusted hosts to connect, thereby reducing exposure of the vulnerable task handlers.

Generated by OpenCVE AI on August 1, 2026 at 08:49 UTC.

Tracking

Advisories

Source	ID	Title
Github GHSA	GHSA-hvrp-rf83-w775	MCP Python SDK: Experimental task handlers allow any client to access and cancel other clients' tasks

Metrics

No CVSS v4.0

Attack Vector Network

Attack Complexity Low

Privileges Required Low

Scope Unchanged

Confidentiality Impact High

Integrity Impact Low

Availability Impact Low

User Interaction None

No CVSS v3.0

No CVSS v2

This CVE is not in the KEV list.

Exploit prediction score: < 1% (0.388% probability within 30 days)

Exploitation none

Automatable no

Technical Impact partial

References

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

History

Jul 16, 2026 2:30 PM Scoring metrics updated View changes

Type	Values Removed	Values Added
Metrics		ssvc `{'options': {'Automatable': 'no', 'Exploitation': 'none', 'Technical Impact': 'partial'}, 'version': '2.0.3'}`

Jul 16, 2026 12:00 AM First appearance in the feed. Affected vendors updated View changes

Type	Values Removed	Values Added
First Time appeared		Modelcontextprotocol Modelcontextprotocol python-sdk
Vendors & Products		Modelcontextprotocol Modelcontextprotocol python-sdk

Jul 15, 2026 8:15 PM Description updated. Title updated. Weaknesses updated. Added references. Scoring metrics updated View changes

Type	Values Removed	Values Added
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.
Title		MCP Python SDK: Experimental task handlers allow any client to access and cancel other clients' tasks
Weaknesses		CWE-862
References		https://github.com/modelcontextprotocol/python-sdk/commit/62137874ff26dd74d2fea80ff528a7fd9ca7a5e7 https://github.com/modelcontextprotocol/python-sdk/pull/2720 https://github.com/modelcontextprotocol/python-sdk/releases/tag/v1.27.2 https://github.com/modelcontextprotocol/python-sdk/security/advisories/GHSA-hvrp-rf83-w775
Metrics		cvssV3_1 `{'score': 7.6, 'vector': 'CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:L/A:L'}`