How severe is GHSA-vj7q-gjh5-988w?

No CVSS score has been assigned to GHSA-vj7q-gjh5-988w yet. Review the advisory details and affected package list to assess your exposure.

Which packages are affected by GHSA-vj7q-gjh5-988w?

GHSA-vj7q-gjh5-988w affects the following packages: mcp (PyPI). Ecosystems affected: PyPI.

How do I fix GHSA-vj7q-gjh5-988w?

Update mcp to 1.28.1 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms GHSA-vj7q-gjh5-988w is resolved across your whole dependency graph.

How do I detect GHSA-vj7q-gjh5-988w in my PyPI dependencies?

Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for mcp, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.

How do I mitigate GHSA-vj7q-gjh5-988w if there is no patch (or I can't update yet)?

If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.

Is GHSA-vj7q-gjh5-988w actively exploited in the wild?

No public exploit code has been indexed for GHSA-vj7q-gjh5-988w yet. This does not mean the vulnerability cannot be exploited — absence of public exploits does not imply safety. Apply the recommended fix and use O3 Security to monitor your exposure.

What is the EPSS score for GHSA-vj7q-gjh5-988w?

GHSA-vj7q-gjh5-988w has an EPSS (Exploit Prediction Scoring System) score of 0.2%, placing it in the 13th percentile of all CVEs. EPSS is maintained by FIRST.org and estimates the probability that a vulnerability will be exploited in the wild within the next 30 days. This score indicates relatively lower exploitation probability, though the CVSS severity should still guide your patching priority.

What type of vulnerability is GHSA-vj7q-gjh5-988w?

GHSA-vj7q-gjh5-988w is classified as CWE-346 (CWE-346), CWE-1385 (CWE-1385). These weakness types describe the underlying flaw category, which helps determine the potential impact and the right class of mitigation.

When was GHSA-vj7q-gjh5-988w published, and has it been updated?

GHSA-vj7q-gjh5-988w was published on July 16, 2026 and was last updated on September 10, 2026. Advisory data evolves as severity scores, affected ranges, and exploit intelligence are revised — always check the latest version of the advisory before acting.

🐍 PyPI

Not in CISA KEV

MCP Python SDK: WebSocket server transport does not support Host/Origin validationGHSA-vj7q-gjh5-988w

Fix: modelcontextprotocol/python-sdk#2992

GHSA-vj7q-gjh5-988w is a CWE-346 vulnerability in mcp. A fix is available for mcp — see the affected versions and patch details below.

Also known asCVE-2026-59950PYSEC-2026-3483

Published

Jul 16, 2026

Updated

Sep 10, 2026

Affected

1 pkg

Patched

1 / 1

Exploits

None indexed

Exploitation data as of Oct 17, 2026 · OSV.dev, NVD, FIRST.org (EPSS)

Exploitation Status

No confirmed exploitation observed yet

A successful exploit gives an attacker total control of the affected component, not partial access.
CISA’s own triage has not observed active exploitation or public proof-of-concept code for this CVE as of its last assessment.

Exploitation and automatability from CISA’s SSVC triage for GHSA-vj7q-gjh5-988w.

EPSS Exploitation Probability

via FIRST.org ↗

0.2%probability of exploitation in next 30 days

Lower Risk0.00%

Lower risk than most CVEs13th percentile — riskier than 13% of all scored CVEsHighest risk

Probability of exploitation in the next 30 days, from FIRST.org EPSS.

Real-World Exposure

1 pkg affected

🐍mcp

Real-time download stats are indexed for npm and PyPI packages. This vulnerability affects PyPI packages — download data is not available via public APIs for these ecosystems.

Description

Summary

In affected versions, the deprecated WebSocket server transport (mcp.server.websocket.websocket_server) accepted the WebSocket handshake without applying any Host or Origin header validation. The TransportSecuritySettings mechanism that the SSE and Streamable HTTP transports use for this purpose was not wired into the WebSocket transport, so there was no SDK-level way to restrict which origins could connect.

Am I affected?

Only if a developer's application server exposes mcp.server.websocket.websocket_server. This transport has never been part of the MCP specification, is marked deprecated, and is not reachable through FastMCP — a developer must have wired it into an ASGI application themselves. Servers using stdio, SSE, or Streamable HTTP are not affected by this advisory.

Details

websocket_server() constructed a Starlette WebSocket and called accept(subprotocol="mcp") immediately, with no inspection of the connection's headers. By contrast, SseServerTransport and StreamableHTTPServerTransport accept an optional security_settings: TransportSecuritySettings and run TransportSecurityMiddleware.validate_request() against the incoming Host and Origin headers before establishing a session. Because browsers attach an Origin header to cross-origin WebSocket upgrade requests but do not enforce a same-origin policy on the response, a web page served from any origin could open a WebSocket to a reachable MCP server on this transport, complete the initialize handshake, and issue JSON-RPC requests on the resulting session.

Impact

A user who runs an MCP server on this transport bound to localhost or a LAN address, without a separate authentication or origin gate in front of it, and visits a malicious web page, can have that page enumerate and invoke the server's tools and read its resources. The consequences depend entirely on what the server exposes. The transport itself requires no token or prior session. Some browsers prompt before allowing a public page to open a connection to a local-network address, which adds a user-interaction step but is not a substitute for server-side validation.

Mitigation

Upgrade to version 1.28.1 or later, in which websocket_server() accepts the same optional security_settings: TransportSecuritySettings argument as the other HTTP-based transports and validates the Host and Origin headers before accepting the handshake; a request that fails validation is rejected with HTTP 403 and ValueError("Request validation failed") is raised to the caller. As with the other transports the parameter defaults to None, which leaves validation disabled, so upgrading alone does not change behaviour: pass a TransportSecuritySettings with enable_dns_rebinding_protection=True and appropriate allowed_hosts / allowed_origins to receive the protection. The recommended path remains to migrate off this deprecated transport to Streamable HTTP, where FastMCP enables this protection automatically for localhost binds. The WebSocket transport has been removed entirely in v2.

Affected Packages

1 total 1 fixed

Ecosystem	Package	Vulnerable range	Fix
🐍PyPI	`mcp`	all versions	1.28.1`pip install --upgrade 'mcp==1.28.1'`

Affected Products

1 product · 1 configurations

Application

mcp python sdklfprojects

< 1.28.1

range

Detection & mitigation playbook

Open-source dependency

Detect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for mcp, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update mcp to 1.28.1 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms GHSA-vj7q-gjh5-988w is resolved across your whole dependency graph.
Workarounds
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.

Frequently Asked Questions

### Summary In affected versions, the deprecated WebSocket server transport (`mcp.server.websocket.websocket_server`) accepted the WebSocket handshake without applying any `Host` or `Origin` header validation. The `TransportSecuritySettings` mechanism that the SSE and Streamable HTTP transports use for this purpose was not wired into the WebSocket transport, so there was no SDK-level way to restrict which origins could connect. ### Am I affected? Only if a developer's application server exposes `mcp.server.websocket.websocket_server`. This transport has never been part of the MCP specificatio

O3 Security · Impact-Aware SCA

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