{
 "public_id": "AIR-2026-0205",
 "incident_id": "2026-08-mcp-go-loopback-host-dns-rebinding",
 "date_disclosed": "2026-08-27",
 "date_occurred": null,
 "title": "CVE-2026-81092: mcp-go served any loopback request regardless of Host, exposing local MCP servers to DNS rebinding",
 "class": "responsible_disclosure",
 "attack_surface": "mcp_server",
 "initial_vector": "malicious_website_dns_rebinding_to_localhost",
 "agent_capability_abused": [
  "tool_invocation",
  "resource_read"
 ],
 "target_product": "mcp-go (Go MCP SDK)",
 "target_vendor": "mcp-go maintainers (mark3labs)",
 "autonomy_level": "assistant",
 "impact_realized": false,
 "impact_type": [
  "unauthorized_tool_invocation",
  "data_access"
 ],
 "blast_radius": "any local MCP server built on mcp-go < 0.56.0 using the StreamableHTTP or SSE transports",
 "cve": [
  "CVE-2026-81092"
 ],
 "taxonomy": {
  "owasp_asi": [
   "ASI04",
   "ASI03"
  ],
  "mitre_atlas": [],
  "labels": [
   "dns_rebinding",
   "missing_host_validation",
   "localhost_exposure",
   "transport_auth_bypass",
   "mcp_sdk"
  ]
 },
 "defense_present": "binding to loopback only, which DNS rebinding defeats without Host validation",
 "defense_bypassed": true,
 "fix_shipped": "mcp-go 0.56.0, which rejects loopback-bound requests carrying a non-loopback Host",
 "primary_sources": [
  "https://github.com/advisories/GHSA-8g5x-gj7x-mxgm"
 ],
 "verified_quote": "StreamableHTTPServer.ServeHTTP in server/streamable_http.go and SSEServer.ServeHTTP in server/sse.go served any request arriving over a loopback connection regardless of the host it named.",
 "confidence": "high",
 "notes": "GHSA-8g5x-gj7x-mxgm, CVSS 7.6 High, published 2026-08-27. Same root cause as CVE-2025-49596 (MCP Inspector) a year earlier, now at the SDK level - evidence that missing Host/Origin validation on localhost MCP transports is a durable class rather than a one-off. Sibling advisories published the same day cover mcp-router (CVE-2026-81094, Critical), mcp-use (CVE-2026-81091), pg-aiguide (CVE-2026-81095) and several MCP servers, all filed as unreviewed.",
 "risk_category": "security_fraud",
 "risk_secondary": [],
 "risk_subcategory": "Server-Side Request Forgery via LLM",
 "risk_sub_secondary": [
  "Unauthorized Access & Account Takeover"
 ],
 "ai_entity": "generative",
 "agency": "ai_as_target",
 "agency_debatable": false,
 "agency_reason": "a missing Host check exposes local MCP servers to DNS rebinding",
 "vector_family": "malicious_component",
 "vector_detail": "malicious_website_dns_rebinding_to_localhost",
 "guardrail_kind": [
  "unknown"
 ],
 "guardrail_outcome": "silent",
 "xrefs": {
  "aiid": [],
  "atlas": [],
  "cve": [
   "CVE-2026-81092"
  ],
  "ghsa": []
 },
 "primary_asi": "ASI04",
 "agent_framework": "mcp_server",
 "model_provider": "unknown",
 "model_name": "",
 "detection_mechanism": "unknown",
 "tool_access": "unknown",
 "financial_loss_band": "unknown",
 "eai_category": "confused_deputy",
 "eai_domain": "access_control_and_permissions",
 "eai_secondary": [],
 "eai_reason": "subcategory: Server-Side Request Forgery via LLM",
 "asi_curated": [],
 "asi_scope": "in_scope",
 "asi_provenance": "rule",
 "asi_reason": "ASI04 (vector_family=malicious_component); ASI03 (eai_category=confused_deputy)",
 "submitted_by": "EAI Internal"
}