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CVE

CVE-2026-34742

DNS Rebinding Protection Disabled by Default in Model Context Protocol Go SDK for Servers Running on Localhost
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CVE

CVE-2026-34742

DNS Rebinding Protection Disabled by Default in Model Context Protocol Go SDK for Servers Running on Localhost

The Model Context Protocol (MCP) Go 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 with StreamableHTTPHandler or SSEHandler, 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 StreamableHTTPHandler or SSEHandler now have this protection enabled by default when binding to localhost. Users are advised to update to version 1.4.0 to receive this automatic protection.

Package Versions Affected

Package Version
patch Availability
No items found.

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CVSS Version

Severity
Base Score
CVSS Version
Score Vector
C
H
U
7.6
-
4.0
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
C
H
U
0
-
3.1
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:N
C
H
U
8.1
-
3.1
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:N

Related Resources

No items found.

References

https://github.com/modelcontextprotocol/go-sdk/security/advisories/GHSA-xw59-hvm2-8pj6, https://nvd.nist.gov/vuln/detail/CVE-2026-34742, https://github.com/modelcontextprotocol/go-sdk/pull/760, https://github.com/modelcontextprotocol/go-sdk/commit/67bd3f2e2b53ce11a16db8d976cdb8ff1e986b6d, https://github.com/modelcontextprotocol/go-sdk, https://github.com/modelcontextprotocol/go-sdk/releases/tag/v1.4.0

Severity

8.1

CVSS Score
0
10

Basic Information

Ecosystem
Base CVSS
8.1
EPSS Probability
0.00029%
EPSS Percentile
0.08873%
Introduced Version
0,v0.1.0,v0.0.0-20250618005433-d2f2f87bbe3d
Fix Available
1.4.0,v1.4.0,v0.0.0-20260213152332-67bd3f2e2b53

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