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High severity · published Jul 15, 2026
CVE-2026-59950
MCP Python SDK: WebSocket server transport does not support Host/Origin validation
8.1
CVSS
0.2%
EPSS
No
On KEV
Description
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.
CVSS vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:N
Attack vector
Network
Complexity
Low
Privileges
None
User interaction
Required
Confidentiality
High
Integrity
High
Availability
None
Scope
Unchanged
Exploitation
Is it being used?
Exploit prediction (EPSS)0.2% · higher than 14% of CVEs
Exploited in the wildNo evidence yet
CISA KEVNot listed
Ransomware campaign useNot known
Affected products
Which versions
PY
python-sdk · modelcontextprotocol
< 1.28.1 · source: vendor
MP
Mcp Python Sdk · Lfprojects
before 1.28.1 · source: NVD
Affected product
PY
python-sdk
modelcontextprotocol
References
NVD
https://nvd.nist.gov/vuln/detail/CVE-2026-59950
CVE.org
https://www.cve.org/CVERecord?id=CVE-2026-59950
Patch
https://github.com/modelcontextprotocol/python-sdk/commit/777b8d06710c140e3606b0d4598e2aa48546c266
Issue Tracking
https://github.com/modelcontextprotocol/python-sdk/pull/2992
Release Notes
https://github.com/modelcontextprotocol/python-sdk/releases/tag/v1.28.1
Vendor Advisory
https://github.com/modelcontextprotocol/python-sdk/security/advisories/GHSA-vj7q-gjh5-988w
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