Vulnerabilities in pkg:golang/github.com/modelcontextprotocol/registry

{
  "schema_version" : "1.4.0",
  "id" : "GHSA-2v5f-5r6w-p67r",
  "modified" : "2026-05-19T15:39:56Z",
  "published" : "2026-05-19T15:39:55Z",
  "aliases" : [ "CVE-2026-45781" ],
  "summary" : "MCP Registry: OCI validator skips ownership check on upstream rate limits",
  "details" : "# OCI ownership validation fails open on upstream rate limits, allowing attacker to claim arbitrary public OCI images under their own namespace\n\nSeverity: Low (re-scored post-triage; see Maintainer triage note below)\nAffected: `modelcontextprotocol/registry` main branch at commit `fe0cb3b` (current HEAD as of 2026-05-09).\nLive deployment: `https://registry.modelcontextprotocol.io` (per repo README).\nRoute: GitHub private security advisory (per repo SECURITY.md).\n\n---\n\n## Title\n\nOCI ownership validation skips label-match check when upstream OCI registry returns HTTP 429, letting any authenticated publisher bind their `io.github.<user>/*` namespace to OCI images they do not control.\n\n## Summary\n\n`internal/validators/registries/oci.go:104-119` fails open on `http.StatusTooManyRequests`: when the\nregistry's anonymous fetch to the upstream OCI registry is rate-limited, `ValidateOCI` returns `nil`\nand the publish is accepted without ever running the\n`io.modelcontextprotocol.server.name` label-match check at lines 122-141. That label check is the\nonly cross-system ownership proof the registry applies to OCI packages — every other registry type\n(NPM, PyPI, NuGet, MCPB) treats a non-200 upstream response as a hard error.\n\nThe fail-open trigger is attacker-controllable. The registry uses `authn.Anonymous` against Docker\nHub, which is rate-limited to 100 manifest pulls per 6 hours per egress IP, and the production\nNGINX rate limit allows 180 publishes/minute (3 RPS, burst 540) per source IP. A single attacker\nfrom a single IP can exhaust the registry's shared anonymous quota in roughly 33 seconds, then\nsubmit a final publish that points `packages[].identifier` at a Docker Hub image they do not own.\nThe validator hits the 429 fail-open branch, returns `nil`, and the registry stores a record under\nthe attacker's namespace claiming the unrelated image as its package payload, with no label proof\nin evidence.\n\nThe fail-open is also reached without an attacker present. Docker Hub routinely 429s busy egress IPs\nduring organic traffic, so publishes during those windows skip OCI ownership validation silently.\n\n## Vulnerable code\n\n`internal/validators/registries/oci.go:97-142`:\n\n```go\nimg, err := remote.Image(ref, remote.WithAuth(authn.Anonymous), remote.WithContext(timeoutCtx))\nif err != nil {\n    if errors.Is(err, context.DeadlineExceeded) {\n        return fmt.Errorf(\"OCI image validation timed out after 30 seconds for '%s'. The registry may be slow or unreachable\", pkg.Identifier)\n    }\n\n    var transportErr *transport.Error\n    if errors.As(err, &transportErr) {\n        switch transportErr.StatusCode {\n        case http.StatusTooManyRequests:\n            // Rate limited - skip validation to avoid blocking publishers\n            // This is intentional: we prioritize UX over strict validation during high traffic\n            log.Printf(\"Skipping OCI validation for %s due to rate limiting\", pkg.Identifier)\n            return nil                                              // <-- FAIL-OPEN\n        case http.StatusNotFound:\n            return fmt.Errorf(\"OCI image '%s' does not exist in the registry\", pkg.Identifier)\n        case http.StatusUnauthorized, http.StatusForbidden:\n            return fmt.Errorf(\"OCI image '%s' is private or requires authentication. Only public images are supported\", pkg.Identifier)\n        }\n    }\n    return fmt.Errorf(\"failed to fetch OCI image: %w\", err)\n}\n\n// Get the image config which contains labels\nconfigFile, err := img.ConfigFile()\nif err != nil {\n    return fmt.Errorf(\"failed to get image config: %w\", err)\n}\n\n// Validate the MCP server name label\nif configFile.Config.Labels == nil {\n    return fmt.Errorf(\"OCI image '%s' is missing required annotation. Add this to your Dockerfile: LABEL io.modelcontextprotocol.server.name=\\\"%s\\\"\", pkg.Identifier, serverName)\n}\n\nmcpName, exists := configFile.Config.Labels[\"io.modelcontextprotocol.server.name\"]\nif !exists {\n    return fmt.Errorf(\"OCI image '%s' is missing required annotation. Add this to your Dockerfile: LABEL io.modelcontextprotocol.server.name=\\\"%s\\\"\", pkg.Identifier, serverName)\n}\n\nif mcpName != serverName {\n    return fmt.Errorf(\"OCI image ownership validation failed. Expected annotation 'io.modelcontextprotocol.server.name' = '%s', got '%s'\", serverName, mcpName)\n}\n```\n\nThe fail-open returns before any of the three label-match guards run.\n\nThe validator is reached on every publish per `internal/service/registry_service.go:151-158`, gated by\n`cfg.EnableRegistryValidation`, which defaults to `true` in `internal/config/config.go:18`.\n\n## Reachability and authorization\n\n`POST /v0/publish` (and `/v0.1/publish`) is registered with bearer-JWT auth in\n`internal/api/handlers/v0/publish.go:30-50`. JWTs are issued by `/v0/auth/github-at`\n(`internal/api/handlers/v0/auth/github_at.go:46-67`), which exchanges any GitHub OAuth access token for\na 5-minute registry JWT carrying `Permission{Action: Publish, ResourcePattern: \"io.github.<login>/*\"}`.\nAny free GitHub account can mint such a JWT, so the publish path is reachable to anyone on the\ninternet at the cost of a GitHub account.\n\n## Trigger conditions\n\n- `internal/validators/registries/oci.go:97`: anonymous Docker Hub auth, subject to the 100\n  manifest-pulls/6h/IP unauthenticated rate limit Docker Hub publishes.\n- `deploy/pkg/k8s/registry.go:330-331`: production NGINX limits incoming requests to 180/minute\n  per source IP with a 3× burst multiplier (540).\n- A single source IP at 3 RPS exhausts the registry's anonymous Docker Hub quota in roughly 33\n  seconds. Each `/publish` against an allowlisted OCI identifier in\n  `internal/validators/registries/oci.go:29-42` (docker.io / registry-1.docker.io / index.docker.io\n  / ghcr.io / quay.io / mcr.microsoft.com / `*.pkg.dev` / `*.azurecr.io`) consumes one slot,\n  including publishes that go on to fail with the missing-annotation error after the manifest is\n  fetched.\n- Once Docker Hub starts returning 429, every subsequent publish hits the fail-open branch until\n  the quota replenishes.\n\n## Attacker chain\n\n1. Free GitHub account `attacker` → `POST /v0/auth/github-at` → registry JWT with\n   `Permission{Action: Publish, ResourcePattern: \"io.github.attacker/*\"}`.\n2. From a single IP, send ~100 publishes whose `packages[].identifier` references real public\n   Docker Hub images that lack the `io.modelcontextprotocol.server.name` label\n   (e.g. `docker.io/library/alpine:latest`, `docker.io/library/nginx:latest`, …). Each publish\n   fails with \"OCI image is missing required annotation\" but consumes one anonymous-quota slot\n   from the registry's shared egress IP.\n3. While the egress IP is rate-limited by Docker Hub, submit the final publish:\n   `name = \"io.github.attacker/<typo-squat-name>\"`,\n   `packages[].registryType = \"oci\"`,\n   `packages[].identifier = \"docker.io/<reputable-org>/<reputable-image>:<tag>\"`.\n4. `ValidateOCI` calls `remote.Image(ref, authn.Anonymous, …)`; Docker Hub returns 429;\n   `transportErr.StatusCode == http.StatusTooManyRequests` matches the fail-open branch;\n   `ValidateOCI` returns `nil`; `ValidatePackage` returns `nil`;\n   `validateRegistryOwnership` returns `nil`; the publish proceeds and `CreateServer` writes the\n   record. The registry now publishes a server record under `io.github.attacker/<typo-squat-name>`\n   that asserts the reputable image as its package payload, without ever inspecting that image's\n   labels.\n\n## Boundary delta\n\n| | Starting capability | After exploit |\n|---|---|---|\n| Identity | Holder of a fresh `io.github.<attacker>` GitHub account | Same |\n| Publish scope | `io.github.<attacker>/*` only | `io.github.<attacker>/*` only (unchanged) |\n| OCI claim scope | OCI images the attacker controls and has labelled with `io.modelcontextprotocol.server.name = io.github.<attacker>/<name>` | **Any public OCI image** at any allowlisted registry, regardless of label |\n\nThe attacker's namespace stays bounded. What changes is that the registry's claim \"this OCI image is\nthe package payload of this MCP server\" is no longer backed by any cross-system proof. The label\ncheck at `oci.go:122-141` is the only ownership proof for OCI packages; bypassing it lets a\npublisher under `io.github.attacker/*` bind a server record to an unrelated image such as\n`docker.io/microsoft/<some-tool>:latest` without ever touching that image. Combined with how MCP\nclients render server-list entries — image identifier shown next to the namespace — the result is\ntypo-squat / impersonation in registry search and discovery surfaces, with the actual image content\ndelivered untouched from its real owner.\n\nThe same fail-open is reached without any attacker action whenever Docker Hub rate-limits the\nregistry's egress IP for organic reasons. In that mode, the OCI ownership check is effectively\nnon-functional for the duration of the limit window, even for legitimate publishers.\n\n## Cross-validator comparison (negative control)\n\nThe other registry-type validators do not fail-open on rate-limit responses:\n\n- `internal/validators/registries/npm.go:72-74` — `if resp.StatusCode != http.StatusOK { return error }`.\n- `internal/validators/registries/pypi.go:76-78` — same shape; 429 surfaces as\n  `\"PyPI package '%s' not found (status: %d)\"`.\n- `internal/validators/registries/nuget.go:253` — non-OK response paths return\n  `\"NuGet README request returned status %d\"`, the publish fails closed.\n- `internal/validators/registries/mcpb.go:84-91` — a HEAD that does not return 200 or a 3xx with\n  `Location` is treated as inaccessible.\n\nOCI is the only validator that converts an upstream rate-limit into a successful ownership\nattestation.\n\n## Suggested fix\n\nTwo options, either alone, or both for defence-in-depth:\n\n1. Remove the fail-open. Replace\n   ```go\n   case http.StatusTooManyRequests:\n       log.Printf(\"Skipping OCI validation for %s due to rate limiting\", pkg.Identifier)\n       return nil\n   ```\n   with an error of the same shape the other validators use (`return fmt.Errorf(\"OCI registry is\n   currently rate-limiting validations for '%s'; please retry shortly\", pkg.Identifier)`). The\n   handler call sites in `validateRegistryOwnership` already propagate the error to a 400 response.\n2. Replace `authn.Anonymous` at `internal/validators/registries/oci.go:97` with an authenticated\n   token whose quota is isolated from organic anonymous traffic to the registry's egress IP. Docker\n   Hub authenticated pulls are 200/6h per token; ghcr.io / quay.io / `*.pkg.dev` / `*.azurecr.io`\n   each have their own auth flows. This removes the easy attacker-side trigger and reduces organic\n   fail-open windows.\n\nIf a fail-open path is retained for UX reasons, queue the publish for re-validation when the\nupstream registry recovers, instead of marking it accepted on first attempt.\n\n## Proof of concept\n\nThe refreshed PoC drives the publish path, not only the validator branch:\n\n```text\nservice.CreateServer\n  -> validators.ValidatePublishRequest\n  -> registries.ValidateOCI\n  -> database.CreateServer\n```\n\nIt runs inside the checked-out module, uses the real service and validator code, and substitutes only\nthe database with a minimal in-memory implementation so the proof can run without a local Postgres\nstack. To keep the proof localhost-only, the runner temporarily adds the in-process mock OCI host to\nthe unexported OCI allowlist. It does not contact Docker Hub, the production registry, or any\nexternal service.\n\nTo run:\n\n```bash\nbash outputs/poc-evidence/2026-05-12-mcp-registry-publish-path/run.sh\n```\n\nCaptured transcript:\n\n```text\n=== modelcontextprotocol/registry publish-path OCI 429 fail-open PoC ===\nPath exercised: service.CreateServer -> validators.ValidatePublishRequest -> registries.ValidateOCI -> DB CreateServer\n\n--- negative control: upstream 404 ---\n[setup] temporarily allowlisted mock OCI host 127.0.0.1:39067 for localhost-only proof\n[setup] publish identifier=127.0.0.1:39067/reputable-org/reputable-image:latest\n[mock-oci] GET /v2/ -> 404\n[publish] rejected: registry validation failed for package 0 (127.0.0.1:39067/reputable-org/reputable-image:latest): OCI image '127.0.0.1:39067/reputable-org/reputable-image:latest' does not exist in the registry\n\n--- BUG: upstream 429 ---\n[setup] temporarily allowlisted mock OCI host 127.0.0.1:40487 for localhost-only proof\n[setup] publish identifier=127.0.0.1:40487/reputable-org/reputable-image:latest\n[mock-oci] GET /v2/ -> 429\n[memdb] AcquirePublishLock(io.github.attacker/typosquat-tool)\n[memdb] CreateServer stored name=io.github.attacker/typosquat-tool version=1.0.1 package=127.0.0.1:40487/reputable-org/reputable-image:latest\n[publish] accepted/stored packages=[{\"registryType\":\"oci\",\"identifier\":\"127.0.0.1:40487/reputable-org/reputable-image:latest\",\"transport\":{\"type\":\"stdio\"}}]\nPUBLISH_PATH_RESULT: ACCEPTED_UNVERIFIED_OCI_PACKAGE_AFTER_429\n```\n\nExit code 0. SHA-256 values:\n\n```text\nacf7121111c19acaca1c99a3c08079213794ffc4feb63e545ec814bd6cd85984  transcript.txt\n340e7a81740e9f14cadc144d4e640a1d497ce3e6696a3d9ea99d63e05c5edd71  publish_path_runner.go\nc970f08d6b79852308ad931da85dd64a65fe373d3c988018de09a7e4c7c345a4  run.sh\n```\n\nThe end-to-end attacker flow against production was not executed. No publish was sent against\n`registry.modelcontextprotocol.io`. No attacker namespace was registered on the live service. The\nlocal proof shows the critical property: when the actual publish validator sees an OCI 429, the\nservice proceeds to create a server record containing the unverified OCI package identifier.\n\n## Severity rationale\n\n**Maintainer triage (2026-05-13):** after review the maintainer settled on Low (3.5, `CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:U/C:N/I:L/A:N`). Impact stays within the attacker's own namespace and image bytes delivered to clients are unchanged. See the comment thread for reasoning. Reporter's original write-up preserved below.\n\nMedium. Auth-bypass class — the attacker bypasses the only ownership proof for OCI packages, and the\nfail-open trigger is attacker-controllable from a single IP at modest cost. The blast radius is\nbounded to publication misrepresentation under the attacker's own namespace; the actual image\ncontent stays under its rightful owner. Combined with normal MCP-client search and discovery\nsurfaces, this is sufficient for impersonation / typo-squat where the rendered image identifier\nimplies authorship the registry could not actually attest.\n\nThe fail-open also activates under normal traffic when Docker Hub rate-limits the egress IP, so the\nOCI ownership check is in practice intermittent rather than absent — both modes are bug states.\n\n## Disclosure preferences\n\nReport through the GitHub Security Advisory process per repo SECURITY.md. Happy to keep details\nprivate until a fix is in motion. If a public GHSA / CVE / release note is published, please credit\nthe report to **Ryan Vonbrubeck / @dodge1218**.",
  "severity" : [ {
    "type" : "CVSS_V3",
    "score" : "CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:U/C:N/I:L/A:N"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "Go",
      "name" : "github.com/modelcontextprotocol/registry"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0"
      }, {
        "fixed" : "1.7.9"
      } ]
    } ]
  } ],
  "references" : [ {
    "type" : "WEB",
    "url" : "https://github.com/modelcontextprotocol/registry/security/advisories/GHSA-2v5f-5r6w-p67r"
  }, {
    "type" : "ADVISORY",
    "url" : "https://nvd.nist.gov/vuln/detail/CVE-2026-45781"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/modelcontextprotocol/registry"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-636" ],
    "severity" : "LOW",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-05-19T15:39:55Z",
    "nvd_published_at" : "2026-05-14T21:16:48Z"
  }
}