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RMCP: DNS rebinding vulnerability in rmcp Streamable HTTP server transport

Type: advisorySources: OSV

RMCP is an official Rust SDK for the Model Context Protocol. Prior to version 1.4.0, the rmcp crate's Streamable HTTP server transport (crates/rmcp/src/transport/streamable_http_server/) did not validate the incoming Host header. This allowed a malicious public website, via a DNS rebinding attack, to send authenticated requests to an MCP server running on the victim's loopback or private-network interface. This vulnerability is fixed in 1.4.0.

Products
Not specified
Affected versions
Not specified
Fixed versions
Not specified
CVEs
CVE-2026-42559
Confirmed fixed CVEs
Not specified
Updated in this feed
3 Nov 2026, 00:00 UTC · Revision 1

Source evidence

RMCP: DNS rebinding vulnerability in rmcp Streamable HTTP server transport

core-osv · Original source

Published 14 May 2026, 14:24 UTC

RMCP is an official Rust SDK for the Model Context Protocol. Prior to version 1.4.0, the rmcp crate's Streamable HTTP server transport (crates/rmcp/src/transport/streamable_http_server/) did not validate the incoming Host header. This allowed a malicious public website, via a DNS rebinding attack, to send authenticated requests to an MCP server running on the victim's loopback or private-network interface. This vulnerability is fixed in 1.4.0.

osv:CVE-2026-42559
Complete source record
{
  "id": "69f93c5e2137097d4f652a09902eed0c7c2c5a4ae578a62d3653abfcf64b8b94",
  "url": "https://osv.dev/vulnerability/CVE-2026-42559",
  "method": "structured",
  "payload": {
    "kind": "advisory",
    "title": "RMCP: DNS rebinding vulnerability in rmcp Streamable HTTP server transport",
    "summary": "RMCP is an official Rust SDK for the Model Context Protocol. Prior to version 1.4.0, the rmcp crate's Streamable HTTP server transport (crates/rmcp/src/transport/streamable_http_server/) did not validate the incoming Host header. This allowed a malicious public website, via a DNS rebinding attack, to send authenticated requests to an MCP server running on the victim's loopback or private-network interface. This vulnerability is fixed in 1.4.0.",
    "evidence": "osv:CVE-2026-42559",
    "products": [],
    "severity": "high",
    "structured": {
      "id": "CVE-2026-42559",
      "aliases": [
        "CVE-2026-42559",
        "GHSA-89vp-x53w-74fx",
        "GHSA-fvh2-gm75-j4j7",
        "RUSTSEC-2026-0140",
        "RUSTSEC-2026-0189"
      ],
      "metrics": [
        {
          "type": "CVSS_V3",
          "score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H"
        }
      ],
      "affected": [
        {
          "ranges": [
            {
              "repo": "https://github.com/modelcontextprotocol/rust-sdk",
              "type": "GIT",
              "events": [
                {
                  "introduced": "0"
                },
                {
                  "fixed": "4628720f89d27a01d4a126ea9f82f0775df9ed52"
                },
                {
                  "fixed": "8e22aa2de28df5a285eed87c11cd89bf15fa90d3"
                }
              ],
              "database_specific": {
                "extracted_events": [
                  {
                    "range": [
                      {
                        "introduced": "0"
                      },
                      {
                        "fixed": "1.4.0"
                      }
                    ],
                    "source": "AFFECTED_FIELD",
                    "strategy": "StringRangeExpression"
                  },
                  {
                    "range": [
                      {
                        "fixed": "8e22aa2de28df5a285eed87c11cd89bf15fa90d3"
                      }
                    ],
                    "source": "REFERENCES_COMMIT"
                  }
                ]
              }
            }
          ],
          "versions": [
            "rmcp-v1.3.0",
            "rmcp-macros-v1.3.0",
            "rmcp-v1.2.0",
            "rmcp-macros-v1.2.0",
            "rmcp-v1.1.1",
            "rmcp-macros-v1.1.1",
            "rmcp-v1.1.0",
            "rmcp-macros-v1.1.0",
            "rmcp-v1.0.0",
            "rmcp-macros-v1.0.0",
            "rmcp-v1.0.0-alpha",
            "rmcp-macros-v1.0.0-alpha",
            "rmcp-v0.17.0",
            "rmcp-macros-v0.17.0",
            "rmcp-v0.16.0",
            "rmcp-macros-v0.16.0",
            "rmcp-v0.15.0",
            "rmcp-macros-v0.15.0",
            "rmcp-v0.14.0",
            "rmcp-macros-v0.14.0",
            "rmcp-v0.13.0",
            "rmcp-macros-v0.13.0",
            "rmcp-v0.12.0",
            "rmcp-macros-v0.12.0",
            "rmcp-v0.11.0",
            "rmcp-macros-v0.11.0",
            "rmcp-v0.10.0",
            "rmcp-macros-v0.10.0",
            "rmcp-v0.9.1",
            "rmcp-macros-v0.9.1",
            "rmcp-v0.9.0",
            "rmcp-macros-v0.9.0",
            "rmcp-v0.8.5",
            "rmcp-macros-v0.8.5",
            "rmcp-v0.8.4",
            "rmcp-macros-v0.8.4",
            "rmcp-v0.8.3",
            "rmcp-macros-v0.8.3",
            "rmcp-v0.8.2",
            "rmcp-macros-v0.8.2",
            "rmcp-v0.8.1",
            "rmcp-macros-v0.8.1",
            "rmcp-v0.8.0",
            "rmcp-macros-v0.8.0",
            "rmcp-v0.7.0",
            "rmcp-macros-v0.7.0",
            "rmcp-v0.6.3",
            "rmcp-macros-v0.6.3",
            "rmcp-v0.6.2",
            "rmcp-macros-v0.6.2",
            "rmcp-v0.6.1",
            "rmcp-macros-v0.6.1",
            "rmcp-v0.6.0",
            "rmcp-macros-v0.6.0",
            "rmcp-v0.5.0",
            "rmcp-macros-v0.5.0",
            "rmcp-v0.4.1",
            "rmcp-macros-v0.4.1",
            "rmcp-v0.4.0",
            "rmcp-macros-v0.4.0",
            "rmcp-v0.3.2",
            "rmcp-macros-v0.3.2",
            "rmcp-v0.3.1",
            "rmcp-macros-v0.3.1",
            "rmcp-v0.3.0",
            "rmcp-macros-v0.3.0",
            "rmcp-v0.2.1",
            "rmcp-macros-v0.2.1",
            "rmcp-v0.2.0",
            "rmcp-macros-v0.2.0"
          ],
          "database_specific": {
            "source": "https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-42559.json"
          }
        }
      ],
      "modified": "2026-10-28T02:30:24.562963667Z",
      "provider": "osv",
      "references": [
        "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/42xxx/CVE-2026-42559.json",
        "https://github.com/modelcontextprotocol/rust-sdk/security/advisories/GHSA-89vp-x53w-74fx",
        "https://nvd.nist.gov/vuln/detail/CVE-2026-42559",
        "https://github.com/modelcontextprotocol/rust-sdk/issues/815",
        "https://github.com/modelcontextprotocol/rust-sdk/issues/822",
        "https://github.com/modelcontextprotocol/rust-sdk/commit/8e22aa2de28df5a285eed87c11cd89bf15fa90d3",
        "https://github.com/modelcontextprotocol/rust-sdk/pull/764"
      ],
      "provider_metadata": {
        "cwe_ids": [
          "CWE-346",
          "CWE-350"
        ],
        "cna_assigner": "GitHub_M",
        "osv_generated_from": "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/42xxx/CVE-2026-42559.json"
      }
    },
    "related_cves": [
      {
        "value": "CVE-2026-42559",
        "evidence": "/id"
      }
    ],
    "security_relevant": true,
    "severity_evidence": "/severity/0/score"
  },
  "source_id": "core-osv",
  "document_id": 491032,
  "published_at": "2026-05-14T14:24:56.09+00:00"
}