Audit signature

Signature Security Auditor

When to Use

• Auditing Solidity contracts using EIP-712 signatures, permits, meta-transactions
• User mentions: signature, ecrecover, EIP-712, permit, nonce, chain_id, deadline, replay, malleability
• Analyzing gasless transactions, delegation systems, authorization mechanisms
• Reviewing contracts with off-chain signing and on-chain verification

Audit Workflow

IMPORTANT: Announce skill usage at the start of analysis

Begin with: "I'm using the audit-signature skill to analyze this contract for signature security vulnerabilities..."

1. Scan for signature operations

   • Search: ecrecover, _hashTypedDataV4, permit, EIP712, signature, v, r, s parameters
   • Focus: signature verification functions, nonce management, parameter inclusion

2. Check against vulnerability patterns

   • Reference reference.md for complete checklist
   • Compare code against example.md

3. Validate exploitability

   • Check access control first - grep for onlyOwner|onlyAdmin|onlyGovernance modifiers
   • Can non-privileged actors exploit signature issues?
   • Can signature be replayed after revocation?
   • Can signature be used on different chains?
   • Are all critical parameters signed?
   • Verify no compensating protections exist
   • Downgrade severity if admin-only unless enables governance attack

4. Generate report

   • Use deliverable template below
   • Include PoC for each finding
   • Rank by severity

Core Vulnerability Patterns

See reference.md for full checklist. Key patterns:

1. Missing nonce replay protection → signatures reused after state changes
2. Cross-chain replay (no chain_id) → same signature valid on all chains
3. Missing critical parameters → unsigned params manipulated by attacker
4. No expiration deadline → lifetime signatures exploitable indefinitely
5. Unchecked ecrecover() return → address(0) passes validation
6. Signature malleability → alternative valid signatures computed without private key

Code examples: See example.md

Severity Criteria

Critical: Missing nonce allowing replay after revocation, unchecked ecrecover() return allowing address(0) to authorize, cross-chain replay enabling unauthorized access on different chains, MUST be exploitable by non-privileged actors High: Missing expiration allowing long-term exploitation, critical parameters (amount, recipient) not included in signature, MUST be exploitable by non-privileged actors Medium: Signature malleability without OpenZeppelin ECDSA, missing parameters in low-impact contexts, admin signature functions with validation issues Low: Nonce implementation suboptimal but functional, documentation issues, admin-only signature issues without user impact

IMPORTANT: Admin-only signature verification functions (onlyOwner, onlyAdmin) are LOW severity unless:

• Missing validation enables unauthorized user to forge admin signatures
• Signature replay/cross-chain issues allow governance takeover
• Unchecked ecrecover in admin function can be exploited via user-facing entry point

False Positives - Do NOT Flag

• OpenZeppelin EIP712 and ECDSA libraries (already secure)
• Signatures with explicit "no expiration by design" documentation for specific use cases
• Internal signature verification with additional access controls
• Test/mock contracts with simplified signature schemes
• Nonces tracked via mapping(address => uint256) with proper increment (valid pattern)

Deliverable Format

MANDATORY: Before deliverable, verify each checklist.md item against codebase. Flag violations as findings.

Use template: templates/report-template.md

Each finding includes: severity, pattern #, file/lines, description, vulnerable code, impact (replay attack, unauthorized access), PoC showing signature reuse or manipulation, remediation, gas impact.

Key Principles

• Nonce uniqueness - every signature consumed exactly once
• Chain-specific - include chain_id in EIP-712 domain
• Complete signing - all relevant parameters in signed message
• Time-bounded - expiration deadlines for all signatures
• Validated recovery - check ecrecover() != address(0)
• Malleability protection - use OpenZeppelin ECDSA library

Output Guidelines

DO:

• Reference specific lines and functions
• Provide executable replay attack PoCs
• Quantify impact (funds at risk, unauthorized operations)
• Show how to compute alternative signatures (malleability)

DON'T:

• Flag OpenZeppelin implementations without modifications
• Report intentional lifetime permits with clear documentation
• Use vague terms ("might be vulnerable")
• Ignore context (additional access controls, trusted signers)