io.github.cyanheads/attack-surface-mcp-server

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[!IMPORTANT] Authorized, defensive use only. Point this server only at assets you own or are explicitly authorized to assess. It performs passive, non-intrusive reconnaissance — it reads public records (Certificate Transparency logs, DNS, RDAP/WHOIS) and each target's own published surface (one TLS handshake and one HTTP GET per host). It does not port-scan, exploit, brute-force, fuzz, or probe for vulnerabilities; that capability is excluded from the surface by design, not gated behind a flag. Output is descriptive — what exists and what the security posture is — never an exploitation plan. Every outbound connection passes an SSRF guard that refuses private, loopback, link-local, and cloud-metadata targets.

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Overview

Passive external attack-surface mapping (EASM) over Certificate Transparency logs, DNS, TLS, HTTP, and RDAP/WHOIS registries, with optional Shodan host intelligence. Discover subdomains, resolve DNS records, and inspect TLS and HTTP security posture across a domain's live hosts. Runs as a stdio process or a local Streamable HTTP server.

Tools

Tool	Description
attacksurface_map_domain	Flagship workflow. Maps a domain's external surface end to end: CT-log subdomain discovery → DNS liveness → (standard+) DNS records, TLS posture, HTTP headers/tech → optional RDAP/WHOIS → (thorough + key) per-IP Shodan enrichment. Returns a structured surface map and a defensive assessment of observable facts.
attacksurface_enumerate_subdomains	Passive subdomain discovery from Certificate Transparency logs (crt.sh → Certspotter → TLS-SAN fallback chain), with DNS resolution to mark which names are live. Per-source provenance; no DNS brute-forcing.
attacksurface_resolve_dns	Resolve and enumerate DNS records (A/AAAA/CNAME/MX/NS/TXT/CAA) for one or more hosts across multiple public resolvers, with optional reverse DNS (PTR). Per-resolver values surface propagation gaps.
attacksurface_inspect_tls	Inspect TLS/SSL posture via a real read-only handshake: protocol, cipher, full certificate chain, SANs, validity window, days-to-expiry, issuer, validation status. Reports invalid/expired/self-signed certs instead of failing.
attacksurface_probe_http	Passive HTTP(S) probe: one GET following redirects. Returns status, redirect chain, headers, a security-header audit (HSTS/CSP/X-Frame-Options/cookie flags/CORS reflection), and an evidence-bound technology fingerprint.
attacksurface_lookup_registration	Registration and ownership lookup via RDAP (JSON; WHOIS fallback). A domain returns registrar, status, lifecycle events, nameservers, DNSSEC; an IP/CIDR returns netblock, allocation CIDRs, origin ASN, country.
attacksurface_lookup_host	Infrastructure intelligence for a single IP (open ports, banners, software versions, ASN, geo) or a faceted internet-wide search, via Shodan. Requires SHODAN_API_KEY — returns a typed source_unavailable error when unset; the rest of the server is unaffected.
attacksurface_recon_guidance	Offline synthesis over findings gathered so far. Returns a prioritized defensive review plan plus pre-filled follow-up calls (which certs to renew, which hosts to inspect, which software versions to check for CVEs against an external NVD/OSV server). No external calls.

Resources

Resource	Description
attacksurface://surface/{domain}	Read-once snapshot of a domain's mapped external surface (subdomains, live hosts, per-host TLS/HTTP posture summary), equivalent to a standard-depth attacksurface_map_domain call.

All resource data is also reachable via tools — tool-only clients lose nothing, since attacksurface_map_domain covers the same ground.

Capability reference

attacksurface_map_domain _tool

• depth control: quick = subdomains + liveness only; standard = + DNS records, TLS, and HTTP posture; thorough = + Shodan enrichment (when a key is present, otherwise skipped with a note)
• includeRegistration adds an RDAP/WHOIS lookup for the apex at standard+ depth
• All per-host fan-out uses Promise.allSettled — one failed source or unreachable host degrades to a note, never tanks the call
• Subdomain resolution is capped (ATTACKSURFACE_MAX_SUBDOMAINS, default 200) with the cap disclosed when hit
• The assessment block synthesizes only observable facts — expiring certs, missing HSTS/CSP, weak TLS versions, failed chain validation — never an exploitation path

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attacksurface_enumerate_subdomains _tool

• Three sources with a fallback chain: crt.sh (primary), Certspotter (fallback — crt.sh is frequently overloaded), and the apex's own TLS certificate SAN list (always available)
• Every discovered name carries its source provenance
• DNS resolution marks which names are live; includeUnresolved: false returns only live hosts
• Reads public logs — it does not brute-force or probe the target's resolvers

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attacksurface_resolve_dns _tool

• Up to 50 hosts per call; queries A, AAAA, CNAME, MX, NS, TXT, and CAA across multiple public resolvers (default 8.8.8.8, 1.1.1.1, 9.9.9.9)
• Reports per-resolver answers so propagation gaps and split-horizon DNS are visible
• Optional reverse DNS (PTR) on resolved addresses
• Each host and resolver IP passes the SSRF guard; a private/loopback resolver IP is rejected as a typed blocked_resolver error; one failing host degrades to a per-host error

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attacksurface_inspect_tls _tool

• Up to 50 hosts per call; port defaults to 443, handshake timeout defaults to 8000ms (1000–30000ms range)
• A real handshake per host reports negotiated protocol and cipher, the full certificate chain, SANs, validity window, days-to-expiry, issuer, and chain-validation status
• Invalid, expired, and self-signed certificates are inspected and reported rather than throwing
• Posture findings flag short expiry windows, deprecated protocols, and self-signed chains
• One handshake per host; no application data is sent; SSRF-guarded

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attacksurface_probe_http _tool

• One http(s):// URL per call; timeout defaults to 10000ms (1000–30000ms range)
• Follows redirects and reports the final status plus the full redirect chain
• Security-header audit: HSTS, CSP, X-Frame-Options, X-Content-Type-Options, Referrer-Policy, Permissions-Policy, cookie Secure/HttpOnly/SameSite flags, and CORS origin-reflection
• Evidence-bound technology fingerprint (server, framework, CDN, WAF, CMS) — every detection names the header or body marker that triggered it
• Strictly one request per host — no path traversal, parameter injection, or multi-method probing; every redirect hop is re-checked against the SSRF guard, surfaced as a typed blocked_target error

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attacksurface_lookup_registration _tool

• target accepts a domain, IP, or CIDR; type (auto / domain / ip) forces interpretation or lets it auto-detect
• RDAP first (structured JSON), WHOIS port-43 fallback for TLDs without RDAP or when a hop is unresponsive
• Domain lookups return registrar, EPP status codes, registration/expiry/updated events, nameservers, and DNSSEC
• IP/CIDR lookups return the netblock name, allocation CIDRs, origin ASN, and country
• Registry data is frequently redacted or sparse — absent fields are reported as unknown, never inferred

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attacksurface_lookup_host _tool

• mode: "host" (default) — a free single-IP lookup: open ports, service banners, software versions, hostnames, ASN, geo
• mode: "search" — a faceted internet-wide query (optional facets) that consumes paid Shodan query credits
• Requires SHODAN_API_KEY; without it the tool returns a typed source_unavailable error and every other tool keeps working
• No Shodan data for the target IP returns a typed no_data error rather than an empty result
• Shodan data reflects Shodan's last scan, not a live port state — the server itself never scans ports

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attacksurface_recon_guidance _tool

• Takes the findings gathered so far (live hosts, TLS/cert state, missing headers, software versions, open ports) and returns a prioritized defensive review plan as markdown plus structured priority items
• Pre-fills concrete follow-up calls — re-inspecting hosts that lack posture data, and chaining disclosed software versions to an external NVD (nist-nvd-mcp-server) or OSV (osv-advisory-mcp-server) server for CVE context
• topic (triage / posture / coverage) shapes plan emphasis; output is a remediation/visibility plan, never an exploitation playbook
• Read-only — no network calls, just reasoning over the supplied state

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attacksurface://surface/{domain} _resource

• Returns application/json: subdomain count, live-host count, and a per-host TLS/HTTP posture summary — equivalent to a standard-depth attacksurface_map_domain call
• Host detail is capped at 50 live hosts; beyond that the response discloses an omitted count and points to attacksurface_map_domain for the full set
• Read-only snapshot; the same data is fully reachable via tools

Features

Built on @cyanheads/mcp-ts-core: stdio and Streamable HTTP transports, pluggable auth (none / jwt / oauth), swappable storage (in-memory, filesystem, Supabase, Cloudflare KV/R2/D1), structured logging with optional OpenTelemetry tracing.

Attack-surface-specific:

• Passive and non-intrusive by mandate — public records plus each target's own single published response; active scanning, exploitation, and brute-forcing are excluded from the surface, not toggled by a flag
• Keyless core — CT subdomain enumeration, DNS, TLS, HTTP/tech, and RDAP/WHOIS all work with zero API keys; Shodan is strictly additive depth
• SSRF guard on every outbound connection — rejects private, loopback, link-local, cloud-metadata, and reserved IPv4/IPv6 ranges before connecting (opt out for trusted internal assessment via ATTACKSURFACE_ALLOW_PRIVATE_TARGETS)
• Multi-source aggregation with fallback chains — CT discovery falls through crt.sh → Certspotter → TLS-SAN; registration falls through RDAP → WHOIS

Agent-friendly output:

• Provenance on every result — source labels (source: crt.sh | certspotter | tls-san, source: rdap | whois) and per-source status so agents can assess completeness and trust
• Graceful partial failure — multi-target and multi-source tools return per-item/per-source error fields and operational notes instead of failing the whole call; only malformed input throws
• Discriminated, typed contracts — typed error reasons (source_unavailable, blocked_target, all_sources_failed) and union output (kind: domain | ip) let callers branch on data, not string parsing
• No fabricated signal — technology detections carry their triggering evidence; absent CT/DNS/RDAP fields are reported as unknown, never inferred

Getting started

Add the following to your MCP client configuration file. Every tool except attacksurface_lookup_host works with no configuration — the keyless core boots on an empty environment.

{
  "mcpServers": {
    "attack-surface-mcp-server": {
      "type": "stdio",
      "command": "bunx",
      "args": ["@cyanheads/attack-surface-mcp-server@latest"],
      "env": {
        "MCP_TRANSPORT_TYPE": "stdio",
        "MCP_LOG_LEVEL": "info"
      }
    }
  }
}

Or with npx (no Bun required):

{
  "mcpServers": {
    "attack-surface-mcp-server": {
      "type": "stdio",
      "command": "npx",
      "args": ["-y", "@cyanheads/attack-surface-mcp-server@latest"],
      "env": {
        "MCP_TRANSPORT_TYPE": "stdio",
        "MCP_LOG_LEVEL": "info"
      }
    }
  }
}

Or with Docker:

{
  "mcpServers": {
    "attack-surface-mcp-server": {
      "type": "stdio",
      "command": "docker",
      "args": ["run", "-i", "--rm", "-e", "MCP_TRANSPORT_TYPE=stdio", "ghcr.io/cyanheads/attack-surface-mcp-server:latest"]
    }
  }
}

To enable Shodan host intelligence (attacksurface_lookup_host), add SHODAN_API_KEY to the env block.

For Streamable HTTP, set the transport and start the server:

MCP_TRANSPORT_TYPE=http MCP_HTTP_PORT=3010 bun run start:http
# Server listens at http://localhost:3010/mcp

Refer to "your MCP client configuration file" generically — different clients use different config paths and this server isn't client-specific.

Prerequisites

• Bun v1.4.0 or higher (or Node.js v24+).
• No API key required for the core tools. Optional: a Shodan API key for attacksurface_lookup_host, and a Certspotter API key to raise CT-fallback rate limits.

Installation

1. Clone the repository:

git clone https://github.com/cyanheads/attack-surface-mcp-server.git

2. Navigate into the directory:

cd attack-surface-mcp-server

3. Install dependencies:

bun install

4. Configure environment (optional):

cp .env.example .env
# edit .env only if you want Shodan, a Certspotter key, or non-default behavior

Configuration

All variables are optional — the server boots and delivers its keyless core with an empty environment.

Variable	Description	Default
SHODAN_API_KEY	Enables attacksurface_lookup_host. Absent → that tool returns source_unavailable; every other tool keeps working.	—
CERTSPOTTER_API_KEY	Raises Certspotter rate limits for the CT-log subdomain fallback. Absent → free unauthenticated tier (rate-limited but functional).	—
ATTACKSURFACE_DEFAULT_RESOLVERS	Comma-separated default DNS resolver IPs for attacksurface_resolve_dns.	8.8.8.8,1.1.1.1,9.9.9.9
ATTACKSURFACE_HTTP_USER_AGENT	Default User-Agent for attacksurface_probe_http (overridable per call).	attack-surface-mcp-server/passive-recon (+https://github.com/cyanheads/attack-surface-mcp-server)
ATTACKSURFACE_MAX_SUBDOMAINS	Cap on subdomains resolved during a map_domain run — bounds fan-out cost.	200
ATTACKSURFACE_RDAP_BOOTSTRAP_URL	RDAP bootstrap base URL; override for a private/mirrored RDAP.	https://rdap.org
ATTACKSURFACE_ALLOW_PRIVATE_TARGETS	Set true to disable the SSRF guard for internal-network assessment. Leave false on any public deployment — it is the safety boundary that keeps the server from being pointed at internal infrastructure.	false
MCP_TRANSPORT_TYPE	Transport: stdio or http.	stdio
MCP_HTTP_PORT	Port for HTTP server.	3010
MCP_SESSION_MODE	HTTP session mode: stateless, stateful, or auto. The server declares stateless; a value set here overrides it. Ignored under stdio.	stateless
MCP_AUTH_MODE	Auth mode: none, jwt, or oauth.	none
MCP_LOG_LEVEL	Log level (RFC 5424).	info
OTEL_ENABLED	Enable OpenTelemetry instrumentation.	false

See .env.example for the full list of optional overrides.

Running the server

Local development

• Build and run:

  # One-time build
  bun run rebuild
  
  # Run the built server
  bun run start:stdio
  # or
  bun run start:http
  

• Run checks and tests:

  bun run devcheck   # Lint, format, typecheck, security
  bun run test       # Vitest test suite
  bun run lint:mcp   # Validate MCP definitions against spec
  

Docker

docker build -t attack-surface-mcp-server .
docker run --rm -e MCP_TRANSPORT_TYPE=http -p 3010:3010 attack-surface-mcp-server

The Dockerfile defaults to HTTP transport, stateless session mode, and logs to /var/log/attack-surface-mcp-server. OpenTelemetry peer dependencies are installed by default — build with --build-arg OTEL_ENABLED=false to omit them.

Project structure

Directory	Purpose
src/index.ts	createApp() entry point — registers tools/resources and inits the six services.
src/config	Server-specific environment variable parsing and validation with Zod.
src/mcp-server/tools	Tool definitions (*.tool.ts).
src/mcp-server/resources	Resource definitions (*.resource.ts).
src/services	Domain service integrations (ct, dns, tls, http, registration, shodan).
src/utils	SSRF guard and input validation.
tests/	Unit and integration tests mirroring src/.

Development guide

See CLAUDE.md/AGENTS.md for development guidelines and architectural rules. The short version:

• Handlers throw, framework catches — no try/catch in tool logic
• Use ctx.log for request-scoped logging, ctx.state for tenant-scoped storage
• Register new tools and resources via the barrels in src/mcp-server/*/definitions/index.ts
• Every outbound connection to a user-supplied target must pass the SSRF guard (assertSafeDomain / assertSafeUrl / assertSafeResolverIp) before connecting
• Wrap external API calls: validate raw → normalize to domain type → return output schema; never fabricate missing fields

Contributing

Issues are welcome. Run checks and tests before submitting:

bun run devcheck
bun run test

License

Apache-2.0 — see LICENSE for details.