CVE-2026-59950 json
MCP Python SDK: WebSocket server transport does not support Host/Origin validation
published 4mo ago modified 18d ago also EUVD-2026-44798 , GHSA-vj7q-gjh5-988w , PYSEC-2026-3483
- cvss
- 8.1
- version 3.1, NVD
- cisa kev
- Not listed
- not in CISA's catalog
- epss
- 0.2%
- EPSS 0.2% chance of exploitation in 30 days, percentile 14%
- public exploits
- 0
- none known
Summary
The MCP Python SDK, called mcp on PyPI, is a Python implementation of the Model Context Protocol (MCP). Prior to 1.28.1, the deprecated mcp.server.websocket.websocket_server transport accepted WebSocket handshakes without applying Host or Origin header validation, leaving no SDK-level way to restrict which origins could connect to applications that exposed that transport. This issue is fixed in version 1.28.1.
Patch / fix
- pypi mcp 1.28.1
- lfprojects mcp_python_sdk 1.28.1
Is CVE-2026-59950 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
- total
- Assessed
- 3mo ago
Exploit prediction
0.23% chance of exploitation in the next 30 days, higher than 14% of all scored CVEs (FIRST EPSS, 2026-11-11).
CVSS scores
| assigned by | version | score | vector |
|---|---|---|---|
| CNA | 4.0 | 7.6 | CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:P/VC:H/VI:H/VA:N/SC:N/SI:N/SA:N |
| CNA | 4.0 | 7.6 | CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:P/VC:H/VI:H/VA:N/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X |
| NVD | 3.1 | 8.1 | CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:N |
Affected packages
| ecosystem | package | affected | fixed in |
|---|---|---|---|
| pypi | mcp | <1.28.1 |
1.28.1 |
Affected products
- modelcontextprotocol python-sdk
Classification
References
-
github.com
/modelcontextprotocol/python-sdk/pull/2992
web, issue-tracking, patch
-
github.com
/modelcontextprotocol/python-sdk/commit/777b8d06710c140e3606b0d4598e2aa48546c266
web, patch
-
github.com
/modelcontextprotocol/python-sdk/security/advisories/GHSA-vj7q-gjh5-988w
web, vendor-advisory, advisory
-
github.com
/modelcontextprotocol/python-sdk/releases/tag/v1.28.1
web, release-notes
-
nvd.nist.gov
/vuln/detail/CVE-2026-59950
advisory
-
github.com
/modelcontextprotocol/python-sdk
package
-
pypi.org
/project/mcp
package
-
github.com
/advisories/GHSA-vj7q-gjh5-988w
advisory
Sources
- CVE List CVE-2026-59950
- GitHub Advisory GHSA-vj7q-gjh5-988w
- NVD CVE-2026-59950
- OSV PYSEC-2026-3483
- Maintainer advisory GHSA-vj7q-gjh5-988w
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.