Vulnerability · Published Jul 15, 2026 · Assigned by GitHub_M

CVE-2026-59950MCP Python SDK: WebSocket server transport does not support Host/Origin validation

High 7.6

In plain English

A high-severity security flaw in python-sdk from modelcontextprotocol. There are no confirmed reports of exploitation so far. The chance it is exploited in the next 30 days is estimated at 0.2% (higher than 14% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.

Severity (CVSS 4.0)7.6High

Exploit odds (30 days)0.2%top 86.0% of all CVEs

Exploited in the wildNo reportsCISA SSVC: none

Attack toolingNoneno public tooling known

Official 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.

Affected packages & fixed versions

Ecosystem	Package	Fixed in	Advisory
PyPI	mcp	1.28.1	GHSA-vj7q-gjh5-988w
PyPI	mcp	1.28.1	PYSEC-2026-3483

Affected products (as reported)

Vendor	Product	Versions
modelcontextprotocol	python-sdk	< 1.28.1

Weakness: CWE-346, CWE-1385 · Vector: 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

References

https://github.com/modelcontextprotocol/python-sdk/security/advisories/GHSA-vj7q-gjh5-988w x_refsource_CONFIRM
https://github.com/modelcontextprotocol/python-sdk/pull/2992 x_refsource_MISC
https://github.com/modelcontextprotocol/python-sdk/commit/777b8d06710c140e3606b0d4598e2aa48546c266 x_refsource_MISC
https://github.com/modelcontextprotocol/python-sdk/releases/tag/v1.28.1 x_refsource_MISC