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CVE

CVE-2026-33252

Cross-Site Tool Execution for HTTP Servers without Authorizatrion in github.com/modelcontextprotocol/go-sdk
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CVE

CVE-2026-33252

Cross-Site Tool Execution for HTTP Servers without Authorizatrion in github.com/modelcontextprotocol/go-sdk

The Go SDK's Streamable HTTP transport accepted browser-generated cross-site POST requests without validating the Origin header and without requiring Content-Type: application/json. In deployments without Authorization, especially stateless or sessionless configurations, this allows an arbitrary website to send MCP requests to a local server and potentially trigger tool execution.

Impact:

A malicious website may have been able to send cross-site POST requests with Content-Type: text/plain, which due to CORS-safelisted properties would reach the MCP message handling without any CORS preflight barrier.

Fix:

The SDK was modified to perform Content-Type header validation for POST requests and introduced a configurable protection for verifying the origin of the request in commit a433a83. Users are advised to update to v1.4.1 to use this additional protection.

Note: v1.4.1 requires Go 1.25 or later.

Credits:

Thank you to Lê Minh Quân for reporting the issue.

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
7.1
-
3.1
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:H/A:L
C
H
U
0
-
3.1
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:H/A:L
C
H
U
7.1
-
3.1
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:H/A:L

Related Resources

No items found.

References

https://github.com/modelcontextprotocol/go-sdk/security/advisories/GHSA-89xv-2j6f-qhc8, https://nvd.nist.gov/vuln/detail/CVE-2026-33252, https://github.com/modelcontextprotocol/go-sdk/commit/a433a831d6e5d5ac3b9e625a8095aa8eaa040dfc, https://github.com/modelcontextprotocol/go-sdk

Severity

7.1

CVSS Score
0
10

Basic Information

Ecosystem
Base CVSS
7.1
EPSS Probability
0.00007%
EPSS Percentile
0.00682%
Introduced Version
0,v0.1.0,v0.0.0-20250618005433-d2f2f87bbe3d
Fix Available
1.4.1,v1.4.1,v0.0.0-20260313103641-a433a831d6e5,7.76.3-r4,18.8.7-r1,18.9.3-r0,18.9.3-r1

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