cobaltosec-corvus 0.9.1

MCP server security testing framework

Corvus

MCP server security testing framework. Tests MCP servers against the OWASP MCP Top 10 — both static analysis and live dynamic probing.

Corvus v0.9.1  MCP Security Scanner
Target     : python my_mcp_server.py
Transport  : stdio
Modules    : tool-poisoning, scope-audit, shadow-tool, supply-chain, auth-audit,
             log-audit, schema-audit, cmd-injection, token-exposure, schema-bypass,
             response-flood, rug-pull, ssrf, endpoint-probe, param-smuggling,
             init-audit, proto-fuzz, output-encoding

Enumerating surface...
  Tools      : 12
  Resources  : 3
  Prompts    : 2
  Server     : my-server 1.0.0

[MCP03] Tool Poisoning (static)
  [HIGH] Potential prompt injection in description of 'execute_code'

[MCP05] Command Injection (dynamic)
  [HIGH] Command injection confirmed in tool 'run_shell', param 'command'
  [MEDIUM] Path traversal accepted in tool 'read_file', param 'path'

...

─── Summary ──────────────────────────────────────────────────────────────────
  CRITICAL  0   HIGH  2   MEDIUM  1   LOW  3   INFO  4
  Session   : corvus-sessions/20260608-143022/

Install

pip install cobaltosec-corvus

Or from source:

git clone https://github.com/CobaltoSec/corvus
cd corvus
pip install -e ".[dev]"

Quick Start

# Scan a stdio MCP server
corvus scan --transport stdio --cmd "python my_server.py"

# Scan an HTTP MCP server
corvus scan --transport http --url http://localhost:8080

# With authentication header
corvus scan --transport http --url http://localhost:8080 --header "Authorization: Bearer token"

# Static analysis only (no live tool calls)
corvus scan --transport stdio --cmd "python my_server.py" --module static

# Specific module
corvus scan --transport stdio --cmd "python my_server.py" --module cmd-injection

# SARIF output (for CI/CD integration)
corvus scan --transport stdio --cmd "python my_server.py" --sarif

# Fail CI on findings above threshold
corvus scan --transport stdio --cmd "python my_server.py" --fail-on high

# Load config from file
corvus scan --config corvus.toml

# Filter low-confidence findings (0-100)
corvus scan --transport stdio --cmd "python my_server.py" --min-confidence 70

# Capture raw JSON-RPC exchanges
corvus scan --transport stdio --cmd "python my_server.py" --log-requests

# List available modules
corvus list-modules

Batch Scan

Scan multiple MCP servers in one invocation:

# targets.yaml
targets:
  - name: filesystem
    transport: stdio
    cmd: ["npx", "-y", "@modelcontextprotocol/server-filesystem", "/tmp"]

  - name: my-http-server
    transport: http
    url: http://localhost:8080

corvus batch targets.yaml --output-dir results/ --sarif --min-confidence 70

Produces a per-target report.json and a top-level summary.md table.

Modules

18 built-in modules covering the full OWASP MCP Top 10 plus protocol and supply chain extensions:

Static modules (no live tool calls)

Name	OWASP	What it tests
tool-poisoning	MCP03	Hidden instructions, obfuscation, and prompt injection patterns in tool descriptions
shadow-tool	EXT03	Tool names and descriptions signaling dangerous operations — namespace squatting, trust hijacking
scope-audit	MCP02	Credential and PII fields in tool inputSchema — tools that request passwords, tokens, or SSNs as parameters
supply-chain	MCP04	Known-vulnerable npm packages extracted from the server command (npm audit)
auth-audit	MCP07	Tool names and descriptions suggesting missing, optional, or bypassable authentication
log-audit	MCP08	Tools exposing or tampering with audit logs — enables anti-forensic techniques or leaks operational data
schema-audit	EXT02	Weak schema definitions (missing required fields, unconstrained types) that expand the attack surface

Dynamic modules (live tool calls)

Name	OWASP	What it tests
cmd-injection	MCP05	Command, path, SQL, and prompt injection payloads per parameter — schema-aware, confirmation-required
token-exposure	MCP01	Credentials, filesystem paths, stack traces, and tokens leaked in tool responses
proto-fuzz	EXT01	Protocol-level crash testing — unknown methods, oversized method names, null request IDs
param-smuggling	EXT01	Hidden parameter backdoors — appends undeclared params and measures behavior differences
schema-bypass	EXT01	Whether tools properly reject inputs that violate their declared schema
ssrf	EXT04	SSRF via URL/host parameters — probes internal metadata endpoints, measures timing anomalies
endpoint-probe	MCP01	Path traversal, SSRF, template injection, and credential exposure via resources/read and prompts/get
output-encoding	MCP10	Invisible Unicode in tool outputs — control chars, zero-width chars, bidi overrides that hide malicious content
response-flood	MCP10	Excessively large or repetitive responses that overflow an LLM context window
rug-pull	MCP06	Re-enumerates the server after dynamic testing; diffs to detect tools added, removed, or mutated mid-session
init-audit	MCP07	Audits the initialize handshake — serverInfo injection chars, protocol version downgrade acceptance

Module groups

# All modules (default)
--module all

# Static only (no live calls to the server)
--module static

# Dynamic only
--module dynamic

# Individual module
--module cmd-injection

Transports

stdio

Spawns the server process and communicates via stdin/stdout. Supports any command:

corvus scan --transport stdio --cmd "python server.py"
corvus scan --transport stdio --cmd "npx @modelcontextprotocol/server-filesystem /tmp"
corvus scan --transport stdio --cmd "uvx my-mcp-server --arg value"

HTTP

Connects to a running HTTP/SSE MCP server:

corvus scan --transport http --url http://localhost:8080

# With auth
corvus scan --transport http --url http://localhost:8080 --header "Authorization: Bearer $TOKEN"
corvus scan --transport http --url http://localhost:8080 --header "X-API-Key: secret"

Config File

Create corvus.toml to avoid repeating CLI flags:

[scan]
transport = "stdio"
cmd = "python my_server.py"
modules = "all"
timeout = 30
sarif = false
fail_on = "high"

[scan.headers]
"Authorization" = "Bearer my-token"

Then run:

corvus scan --config corvus.toml

CLI flags override config file values. The --config flag also accepts absolute paths.

CLI Reference

Usage: corvus scan [OPTIONS]

 Scan an MCP server for security vulnerabilities.

Options:
  -t, --transport  TEXT     stdio | http  (overrides config)
  --cmd            TEXT     Command to launch MCP server (stdio)
  --url            TEXT     URL of MCP server (http)
  -m, --module     TEXT     all | static | dynamic | <module-name>  (overrides config)
  -o, --output-dir PATH
  --fail-on        TEXT     Exit 1 if findings at this severity or above
                            (critical|high|medium|low)
  --timeout        INTEGER  Request timeout in seconds (overrides config)
  --sarif                   Also write SARIF 2.1.0 report
  --header         TEXT     HTTP header "Key: Value" (repeatable, for http transport)
  -c, --config     PATH     Path to corvus.toml config file
  --plugin-dir     TEXT     Directory to load external modules from (repeatable)
  --help                    Show this message and exit.

Other commands:

corvus list-modules              # list available modules with OWASP ID and type
corvus list-modules --plugin-dir ./plugins/   # include external plugins
corvus version                   # print version

Output

Each scan creates a session directory under corvus-sessions/<timestamp>/:

corvus-sessions/20260608-143022/
├── report.json     # full structured result
├── report.md       # human-readable with remediation guidance
└── report.sarif    # SARIF 2.1.0 (only when --sarif is passed)

SARIF integration

SARIF output is compatible with GitHub Advanced Security, VS Code SARIF Viewer, and any CI pipeline that consumes SARIF:

# GitHub Actions example
- name: Run Corvus
  run: corvus scan --transport stdio --cmd "python server.py" --sarif --fail-on high

- name: Upload SARIF
  uses: github/codeql-action/upload-sarif@v3
  with:
    sarif_file: corvus-sessions/

CI Integration

# Exit 1 if any CRITICAL findings
corvus scan --transport stdio --cmd "python server.py" --fail-on critical

# Exit 1 if any HIGH or above
corvus scan --transport stdio --cmd "python server.py" --fail-on high

Severity levels (ascending): info → low → medium → high → critical

Plugin System

Add custom modules without modifying Corvus source.

Directory-based plugins

corvus scan --transport stdio --cmd "python server.py" --plugin-dir ./my-modules/

Each .py file in the directory is loaded as a module. The file must define a class that inherits from BaseModule:

from corvus.modules.base import BaseModule, Finding, Severity

class MyCustomModule(BaseModule):
    name = "my-check"
    owasp_id = "MCP-CUSTOM"
    module_type = "static"
    description = "Custom check for my organization"

    async def run(self, surface, transport):
        findings = []
        for tool in surface.tools:
            if "dangerous_pattern" in tool.description:
                findings.append(Finding(
                    rule_id="MY001",
                    tool_name=tool.name,
                    severity=Severity.HIGH,
                    title="Dangerous pattern detected",
                    description=f"Tool '{tool.name}' contains a dangerous pattern.",
                    remediation="Remove or sanitize the pattern.",
                ))
        return findings

Package-based plugins

Register via pyproject.toml entry points:

[project.entry-points."corvus.modules"]
my-check = "my_package.modules.my_check:MyCustomModule"

After pip install my-package, Corvus auto-discovers the module.

Research: MCP Ecosystem Security Audit

Corvus has been battle-tested against the real-world MCP ecosystem across two case studies — 43 servers audited, spanning official @modelcontextprotocol packages, community servers, and the broader npm ecosystem.

	CS01 (Tier A/B/C)	CS02 (Tier D)	Combined
Servers audited	23	20	43
True positives	43	12	55
HIGH findings	27	10	37
CRITICAL findings	1	0	1
FP rate	30.6%	40%	~34%

Key findings from the wild:

• 35% of MCP servers crash on a single malformed JSON-RPC request — reproducible DoS with no authentication required
• Shadow tool injection confirmed in mcp-server-docker, postgres-mcp-server, lsp-mcp-server — tool descriptions that instruct an AI agent to execute arbitrary operations
• Supply chain cascade: @modelcontextprotocol/sdk ≤1.25.1 advisory propagates to the majority of JS-based servers in the ecosystem
• Invisible Unicode (zero-width chars, bidi overrides) in tool descriptions — undetectable to human reviewers, can manipulate AI agent reasoning
• 65% of audited servers have at least one HIGH-severity confirmed finding

Full datasets, curated findings, and methodology in case-studies/.

Responsible Disclosure

Advisory	Package	Finding	Status
GHSA-mf64-cgv4-ppcx	@playwright/mcp	Path traversal via filesystem tools	Coordinated disclosure (MSRC)
GHSA-7w27-7xwv-x6x2	mcp-server-sqlite	SQL injection via query tools	Disclosed
GHSA-7763-c5gf-v5fj	mcp-shell-server	Command injection via shell tools	Disclosed
GHSA-pr6r-h66r-m47j	server-everything	Token exposure via env tool	Disclosed

Development

git clone https://github.com/CobaltoSec/corvus
cd corvus
pip install -e ".[dev]"
pytest

License

MIT