CVE-2026-59950Network attack vector

Unauthorized tool invocation via unvalidated WebSocket origins

Published Jul 15, 2026 · Updated Jul 15, 2026

Origin validation error in MCP Python SDK before 1.28.1 allows remote attackers to invoke exposed server tools through WebSockets. The websocket_server function immediately accepts the Starlette WebSocket without inspecting Host or Origin headers or calling TransportSecurityMiddleware. Exploitation requires an application to mount this deprecated transport without a separate gate and a user to visit a malicious page; accessible resources and tool effects depend on that server.

CVSS severity7.6
High
EPSS probability0.23%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Origin validation error in MCP Python SDK before 1.28.1 allows remote attackers to invoke exposed server tools through WebSockets. The websocket_server function immediately accepts the Starlette WebSocket without inspecting Host or Origin headers or calling TransportSecurityMiddleware. Exploitation requires an application to mount this deprecated transport without a separate gate and a user to visit a malicious page; accessible resources and tool effects depend on that server.

The record

CVE
CVE-2026-59950
Published
Jul 15, 2026
Updated
Jul 15, 2026
Vendor
Model Context Protocol
Product
MCP Python SDK
Classifications
CWE-1385, CWE-346, T1189
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Jul 15, 2026CVE publishedPublication date reported by the CVE source.
  2. Jul 15, 2026Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=< 1.28.1

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Model Context Protocol · MCP Python SDKversion=< 1.28.1

Published CVSS scores

8.1NIST NVDCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:N
7.6GitHub, Inc.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

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-1385Missing Origin Validation in WebSockets
CWE-346Origin Validation Error
T1189Drive-by Compromise

Public exploit references

No public exploit references are available in this record.

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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