critical9.4
CVE-2026-9739
Vulnerable to DNS rebinding attacks when using SSE (http://b/499408790).
Impact
Vulnerable to DNS rebinding attacks when using SSE (http://b/499408790). During the beta phase, we implemented `allowed-origins` and `allowed-hosts` flags to align with MCP security guidelines. However, the hardcoded `Access-Control-Allow-Origin: *` header in the SSE initialization handler was inadvertently retained. This vulnerability specifically impacts users connecting via Toolbox using SSE under specification v2024-11-05.
Affected packages
| Ecosystem | Package | Affected | Fixed in |
|---|---|---|---|
| go | github.com/googleapis/mcp-toolbox | < 1.2.0 | 1.2.0 |
Weakness classification
References
- NVD record
- CVE.org record
- GitHub advisory
- https://github.com/advisories/GHSA-7pf3-8xx7-rvhf
- https://nvd.nist.gov/vuln/detail/CVE-2026-9739
- https://github.com/googleapis/mcp-toolbox/issues/3053
- https://github.com/googleapis/mcp-toolbox/pull/3054
- https://github.com/googleapis/mcp-toolbox/commit/c4c7bd917e686de68e2be866cfe3872c3439efae