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MCP Python SDK CVE-2026-59950

| EUVDEUVD-2026-44798 HIGH
Origin Validation Error (CWE-346)
2026-07-15 GitHub_M
Python Information Disclosure Python Sdk
7.6
CVSS 4.0 · Vendor: GitHub_M
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Severity by source

Vendor (GitHub_M) PRIMARY
7.6 HIGH
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
vuln.today AI
6.8 MEDIUM

Network-reachable and unauthenticated (PR:N), but AC:H and UI:R reflect the required cross-origin/DNS-rebinding setup and a victim loading attacker content; high C/I on hijacked MCP tools, no availability impact.

3.1 AV:N/AC:H/PR:N/UI:R/S:U/C:H/I:H/A:N
4.0 AV:N/AC:L/AT:P/PR:N/UI:P/VC:H/VI:H/VA:N/SC:N/SI:N/SA:N

Primary rating from Vendor (GitHub_M).

CVSS VectorVendor: GitHub_M

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
Attack Vector
Network
Attack Complexity
Low
Privileges Required
None
User Interaction
P
Scope
X

Lifecycle Timeline

4
Patch available
Jul 15, 2026 - 22:33 EUVD
Source Code Evidence Fetched
Jul 15, 2026 - 21:01 vuln.today
Analysis Generated
Jul 15, 2026 - 21:01 vuln.today
CVE Published
Jul 15, 2026 - 20:08 cve.org
HIGH 7.6

DescriptionCVE.org

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.

Articles & Coverage 1

News 7 New Python Vulnerabilities - 7 High Severity, No Public POC Jul 16, 2026

AnalysisAI

Cross-origin WebSocket hijacking in the Model Context Protocol Python SDK (mcp on PyPI) before 1.28.1 lets a remote web page connect to any application exposing the deprecated mcp.server.websocket.websocket_server transport, because that transport accepted handshakes without Host or Origin validation and offered no SDK-level control to restrict connecting origins. A malicious site loaded in a victim's browser can therefore open an MCP session against a locally reachable server and drive its tools. …

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Attack ChainAIDerived

Hypothetical attack flow derived from CVE metadata

Access
Attacker hosts malicious web page
Delivery
Victim browser loads the page
Exploit
Script opens cross-origin WebSocket to local MCP server
Execution
Handshake accepted without Origin/Host check
Impact
Drive MCP tool calls to read/exfiltrate data
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Vulnerability AssessmentAI

Exploitation Exploitation requires that the target application expose the deprecated mcp.server.websocket.websocket_server transport from mcp < 1.28.1 (applications using only SSE or Streamable HTTP transports are not affected). … Additional conditions and limiting factors are described in the full assessment.
Risk Assessment The supplied CVSS 4.0 vector (CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:P/VC:H/VI:H/VA:N, score 7.6) captures the shape of this well: network reachable and unauthenticated (PR:N), but gated by an attack requirement (AT:P) and passive user interaction (UI:P) - i.e., a victim must load attacker content in a browser, and the target must run the specific deprecated transport. … Full risk analysis with EPSS, KEV, and SSVC signal comparison available after sign-in.
Exploit Scenario A developer runs an MCP-enabled application that exposes the deprecated websocket_server transport on localhost. The developer visits an attacker-controlled web page, whose JavaScript opens a cross-origin WebSocket to ws://127.0.0.1:<port>/ws with subprotocol 'mcp'; because no Origin check is applied, the handshake succeeds and the page drives MCP tool calls to read data or trigger actions. …
Remediation Vendor-released patch: 1.28.1 - upgrade the mcp PyPI package to 1.28.1 or later (pip install --upgrade 'mcp>=1.28.1'). … Detailed patch versions, workarounds, and compensating controls in full report.
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Recommended ActionAI

Within 24 hours, inventory all systems running mcp Python SDK, identify instances running versions before 1.28.1 using the deprecated mcp.server.websocket.websocket_server transport, and assess network exposure and business criticality. …

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CVE-2026-59950 vulnerability details – vuln.today
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