vyper-guard 0.3.0

Real-time vulnerability monitoring and auto-remediation for Vyper smart contracts

Vyper Guard

Vyper Guard is a lightweight static security analyzer for Vyper smart contracts. It scans .vy files and highlights insecure patterns, logic risks, and best-practice violations before deployment.

The goal is to give developers quick feedback directly from the terminal while writing contracts.

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Installation

Install the CLI globally using pip:

pip install vyper-guard

Verify installation:

vyper-guard --help

If installed correctly, the CLI help menu will appear.

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Basic Usage

Analyze a single contract:

vyper-guard analyze contract.vy

Example:

vyper-guard analyze vault.vy

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Analyze a Folder

Scan all Vyper contracts inside a directory:

vyper-guard analyze contracts/

The tool will recursively scan all .vy files.

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Output Formats

# Rich terminal output (default)
vyper-guard analyze contract.vy

# JSON report
vyper-guard analyze contract.vy --format json --output report.json

# Markdown report
vyper-guard analyze contract.vy --format markdown --output report.md

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Example Output

========================================
VYPER GUARD SECURITY REPORT
========================================

File: vault.vy

Security Score: 14 / 100
Risk Level: CRITICAL
Recommendation: DO NOT DEPLOY

----------------------------------------
Severity Breakdown
----------------------------------------

CRITICAL : 2
HIGH     : 3
MEDIUM   : 2
LOW      : 1

----------------------------------------
Findings
----------------------------------------

[CRITICAL] Reentrancy vulnerability
Line: 42
Issue:
External call happens before state update.

Fix:
Follow Checks-Effects-Interactions pattern
or use @nonreentrant.

----------------------------------------

[HIGH] Unsafe raw_call usage
Line: 42
Issue:
raw_call used without proper checks.

Fix:
Validate return value or avoid raw_call.

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What Vyper Guard Detects

Security Issues

• Reentrancy risks
• Unsafe raw_call
• Delegatecall misuse
• Unprotected selfdestruct
• Unprotected state modification
• Unchecked subtraction / integer overflow

Logic & Best Practices

• Checks-Effects-Interactions violations
• Timestamp dependence
• Value transfers inside loops
• Missing reentrancy guards
• Missing event emission
• Known compiler version bugs

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Detectors

#	Detector	Severity	What It Finds
1	missing_nonreentrant	CRITICAL	External functions with value transfers but no @nonreentrant
2	unsafe_raw_call	HIGH	raw_call() without return value checks
3	missing_event_emission	LOW	State-changing functions that emit no event
4	timestamp_dependence	LOW	block.timestamp used in conditional logic
5	integer_overflow	HIGH	unsafe_add, unsafe_sub, unsafe_mul, unsafe_div usage
6	unprotected_selfdestruct	CRITICAL	selfdestruct() without access control
7	dangerous_delegatecall	HIGH	raw_call() with is_delegate_call=True
8	unprotected_state_change	HIGH	Writes to sensitive state without msg.sender check
9	send_in_loop	HIGH	send() / raw_call() inside for loops
10	unchecked_subtraction	HIGH	self.x -= amount without overflow guard
11	cei_violation	HIGH	External call before state update
12	compiler_version_check	HIGH / INFO	Known Vyper compiler CVEs (GHSA-5824, GHSA-vxmm)

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Security Score

Each contract receives a 0-100 security score.

Score	Grade	Meaning
90-100	A+	Production ready
75-89	A	Minor fixes needed
60-74	B	Review required
45-59	C	Risky - major fixes needed
< 45	F	Do not deploy

The score decreases based on detected vulnerability severity:

Severity	Penalty per finding
CRITICAL	-40
HIGH	-20
MEDIUM	-8
LOW	-3
INFO	-1

Each severity tier is capped to prevent a single category from dominating the score.

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CLI Commands

Command	Description
vyper-guard analyze <file>	Scan a contract for vulnerabilities
vyper-guard analyze <file> --fix	Scan and auto-fix vulnerabilities
vyper-guard stats <file>	Show contract structure and complexity
vyper-guard diff <file1> <file2>	Compare security posture of two contracts
vyper-guard detectors	List all available detectors
vyper-guard init	Create a .guardianrc config file
vyper-guard monitor <address>	Live-monitor a deployed contract
vyper-guard baseline <address>	Build normal-behaviour baseline
vyper-guard version	Show version and environment info

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What To Do After a Scan

After running Vyper Guard:

1. Review all CRITICAL issues first.
2. Fix HIGH severity vulnerabilities before deployment.
3. Improve MEDIUM and LOW issues to increase security score.
4. Re-run the scan until the contract reaches a safe score.

Recommended minimum score for production: 80+

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Typical Workflow

1. Write Vyper contract
2. Run vyper-guard analyze contract.vy
3. Fix reported vulnerabilities
4. Re-run scan
5. Deploy when score is acceptable

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Auto-Remediation

vyper-guard analyze contract.vy --fix

This will:

1. Run all detectors
2. Generate fixes (decorators, guards, events, pragmas)
3. Show a unified diff for each fix
4. Write patched code to contract.fixed.vy
5. Prompt before overwriting the original

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Live Monitoring

# Monitor a deployed contract
vyper-guard monitor 0xAddr --rpc https://mainnet.infura.io/v3/KEY

# Build a baseline first
vyper-guard baseline 0xAddr --rpc https://rpc.url --duration 300

# Monitor with Slack alerts
vyper-guard monitor 0xAddr --rpc https://rpc.url \
  --alert-webhook https://hooks.slack.com/...

Requires: pip install vyper-guard[monitor]

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CI Mode

vyper-guard analyze contract.vy --ci --severity-threshold HIGH

Exit code 1 if any findings match or exceed the threshold - use in GitHub Actions or any CI pipeline.

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Pre-commit Hook

Add to .pre-commit-config.yaml:

repos:
  - repo: https://github.com/preethamak/vyper
    rev: v0.3.0
    hooks:
      - id: vyper-guard

Every commit touching .vy files will be scanned automatically.

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Example Vulnerability Fix

Bad pattern:

raw_call(msg.sender, b"", value=balance)
self.balances[msg.sender] = 0

Safer pattern:

self.balances[msg.sender] = 0
raw_call(msg.sender, b"", value=balance)

Or use a reentrancy guard:

@nonreentrant("lock")

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Limitations

Vyper Guard performs pattern-based static analysis.

This means:

• It detects known risky patterns
• It does not compile or execute contracts
• Some complex vulnerabilities may require manual review

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Disclaimer

Vyper Guard helps identify common vulnerabilities but does not guarantee contract security.

Always combine automated scanning with manual audits before deploying smart contracts.

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License

MIT