CVE-2026-52870 json
MCP Python SDK: Experimental task handlers allow any client to access and cancel other clients' tasks
published 5mo ago modified 18d ago also EUVD-2026-44797 , GHSA-hvrp-rf83-w775 , PYSEC-2026-3481
- cvss
- 7.6
- version 3.1, CNA
- cisa kev
- Not listed
- not in CISA's catalog
- epss
- 0.4%
- EPSS 0.4% chance of exploitation in 30 days, percentile 33%
- public exploits
- 0
- none known
Summary
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.
Patch / fix
- pypi mcp 1.27.2
- lfprojects mcp_python_sdk 1.27.2
Is CVE-2026-52870 in your dependencies? Fencer shows which of your repositories are affected as soon as an advisory lands, and opens the fix as a pull request.
Check with FencerCISA SSVC
- Exploitation
- none
- Automatable
- no
- Technical impact
- partial
- Assessed
- 3mo ago
Exploit prediction
0.39% chance of exploitation in the next 30 days, higher than 33% of all scored CVEs (FIRST EPSS, 2026-11-11).
CVSS scores
| assigned by | version | score | vector |
|---|---|---|---|
| CNA | 3.1 | 7.6 | CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:L/A:L |
| GitHub | 3.1 | 7.6 | CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:L/A:L |
| OSV | 3.1 | 7.6 | CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:L/A:L |
Affected packages
| ecosystem | package | affected | fixed in |
|---|---|---|---|
| pypi | mcp | >=1.23.0, <1.27.2 |
1.27.2 |
Affected products
- modelcontextprotocol python-sdk
Classification
- Weakness
-
- CWE-862 Missing Authorization
References
-
github.com
/modelcontextprotocol/python-sdk/pull/2720
web, issue-tracking, patch
-
github.com
/modelcontextprotocol/python-sdk/commit/62137874ff26dd74d2fea80ff528a7fd9ca7a5e7
web, patch
-
github.com
/modelcontextprotocol/python-sdk/security/advisories/GHSA-hvrp-rf83-w775
web, vendor-advisory, advisory
-
github.com
/modelcontextprotocol/python-sdk/releases/tag/v1.27.2
web, release-notes
-
nvd.nist.gov
/vuln/detail/CVE-2026-52870
advisory
-
github.com
/modelcontextprotocol/python-sdk
package
-
pypi.org
/project/mcp
package
-
github.com
/advisories/GHSA-hvrp-rf83-w775
advisory
Sources
- CVE List CVE-2026-52870
- GitHub Advisory GHSA-hvrp-rf83-w775
- NVD CVE-2026-52870
- OSV PYSEC-2026-3481
- Maintainer advisory GHSA-hvrp-rf83-w775
Fencer Intel keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.
The maintainers of modelcontextprotocol/python-sdk published their own advisory on GitHub. Reviewed sources take precedence over it.