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CVE-2026-52870 modelcontextprotocol CVE debrief

The MCP Python SDK, called mcp on PyPI, has a high-severity vulnerability tracked as CVE-2026-52870. From version 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. This allows any connected client to enumerate, read results from, consume messages for, or cancel other clients' tasks. The issue is fixed in version 1.27.2.

Vendor
modelcontextprotocol
Product
python-sdk
CVSS
HIGH 7.6
CISA KEV
Not listed in stored evidence
Original CVE published
2026-07-15
Original CVE updated
2026-07-17
Advisory published
2026-07-15
Advisory updated
2026-07-17

Who should care

Users of the MCP Python SDK, particularly those who have installed the mcp package from PyPI and are using versions between 1.23.0 and 1.27.2, should be aware of this vulnerability and take immediate action to upgrade to version 1.27.2 or later.

Technical summary

The MCP Python SDK's server.experimental.enable_tasks() function installs default handlers for tasks/list, tasks/get, tasks/result, and tasks/cancel. However, these handlers only operate on task identifiers and do not record the session that created each task. This oversight allows any connected client to enumerate, read results from, consume messages for, or cancel tasks created by other clients. The vulnerability has a CVSS score of 7.6 and is classified as HIGH severity.

Defensive priority

High priority should be given to upgrading the MCP Python SDK to version 1.27.2 or later. In the meantime, users can consider implementing compensating controls, such as monitoring for suspicious task-related activity or restricting access to task management functions.

Recommended defensive actions

  • Upgrade to MCP Python SDK version 1.27.2 or later
  • Review and restrict access to task management functions
  • Monitor for suspicious task-related activity
  • Confirm whether affected product deployments exist in managed environments and assign an owner for follow-up
  • Review the supplied official advisory or CVE record to validate affected scope, severity, and vendor guidance
  • Plan vendor-supported updates or mitigations through normal change control where exposure is confirmed
  • Check relevant monitoring, detection, and logs for exposed assets that need extra review

Evidence notes

The CVE record was published on 2026-07-15T20:17:38.577Z and was last modified on 2026-07-16T14:16:53.680Z. The NVD entry is currently Undergoing Analysis. The vulnerability was fixed in version 1.27.2 of the MCP Python SDK.

Sources and references

Verified primary and authoritative sources

  • CVE-2026-52870 CVE Program record

    Publisher, destination, and source semantics verified

    URL: https://www.cve.org/CVERecord?id=CVE-2026-52870

    CVE Program - Official CVE Program record with source-provided CVE metadata.

  • CVE-2026-52870 NVD vulnerability detail

    Publisher, destination, and source semantics verified

    URL: https://nvd.nist.gov/vuln/detail/CVE-2026-52870

    NIST National Vulnerability Database - Official NIST NVD detail page and source-specific vulnerability assessment.

Supplemental references

Methodology and review provenance

AI-assisted synthesis based on stored public vulnerability evidence. System validation, approval state, and publication status do not by themselves establish human review of this revision. PatchSiren helps prioritize defensive review and does not prove exposure or remediation on any system.