GHSA-9h52-p55h-vw2f

Suggest an improvement
Source
https://github.com/advisories/GHSA-9h52-p55h-vw2f
Import Source
https://github.com/github/advisory-database/blob/main/advisories/github-reviewed/2025/12/GHSA-9h52-p55h-vw2f/GHSA-9h52-p55h-vw2f.json
JSON Data
https://api.test.osv.dev/v1/vulns/GHSA-9h52-p55h-vw2f
Aliases
Related
Published
2025-12-02T16:52:08Z
Modified
2026-01-30T01:28:51.658622Z
Severity
  • 7.6 (High) CVSS_V4 - 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 Calculator
Summary
Model Context Protocol (MCP) Python SDK does not enable DNS rebinding protection by default
Details

Description

The Model Context Protocol (MCP) Python SDK does not enable DNS rebinding protection by default for HTTP-based servers. When an HTTP-based MCP server is run on localhost without authentication using FastMCP with streamable HTTP or SSE transport, and has not configured TransportSecuritySettings, a malicious website could exploit DNS rebinding to bypass same-origin policy restrictions and send requests to the local MCP server. This could allow an attacker to invoke tools or access resources exposed by the MCP server on behalf of the user in those limited circumstances.

Note that running HTTP-based MCP servers locally without authentication is not recommended per MCP security best practices. This issue does not affect servers using stdio transport.

Servers created via FastMCP() now have DNS rebinding protection enabled by default when the host parameter is 127.0.0.1 or localhost. Users are advised to update to version 1.23.0 to receive this automatic protection. Users with custom low-level server configurations using StreamableHTTPSessionManager or SseServerTransport directly should explicitly configure TransportSecuritySettings when running an unauthenticated server on localhost.

Database specific 
{
    "github_reviewed": true,
    "nvd_published_at": "2025-12-02T19:15:52Z",
    "severity": "HIGH",
    "github_reviewed_at": "2025-12-02T16:52:08Z",
    "cwe_ids": [
        "CWE-1188",
        "CWE-350"
    ]
}
References

Affected packages

PyPI / mcp

Package

Name
mcp
View open source insights on deps.dev
Purl
pkg:pypi/mcp

Affected ranges

Type
ECOSYSTEM
Events
Introduced
0Unknown introduced version / All previous versions are affected
Fixed
1.23.0

Affected versions

0.*
0.9.1
1.*
1.0.0
1.1.0
1.1.1
1.1.2
1.1.3
1.2.0rc1
1.2.0
1.2.1
1.3.0rc1
1.3.0
1.4.0
1.4.1
1.5.0
1.6.0
1.7.0
1.7.1
1.8.0
1.8.1
1.9.0
1.9.1
1.9.2
1.9.3
1.9.4
1.10.0
1.10.1
1.11.0
1.12.0
1.12.1
1.12.2
1.12.3
1.12.4
1.13.0
1.13.1
1.14.0
1.14.1
1.15.0
1.16.0
1.17.0
1.18.0
1.19.0
1.20.0
1.21.0
1.21.1
1.21.2
1.22.0

Database specific

source 
"https://github.com/github/advisory-database/blob/main/advisories/github-reviewed/2025/12/GHSA-9h52-p55h-vw2f/GHSA-9h52-p55h-vw2f.json"