Systematically scan Cairo smart contracts on StarkNet for platform-specific security vulnerabilities related to arithmetic, cross-layer messaging, and cryptographic operations. This skill encodes 6 critical vulnerability patterns unique to Cairo/StarkNet ecosystem.
\n.cairo// Cairo contract indicators\n#[contract]\nmod MyContract {\n use starknet::ContractAddress;\n\n #[storage]\n struct Storage {\n balance: LegacyMap<ContractAddress, felt252>,\n }\n\n #[external(v0)]\n fn transfer(ref self: ContractState, to: ContractAddress, amount: felt252) {\n // Contract logic\n }\n\n #[l1_handler]\n fn handle_deposit(ref self: ContractState, from_address: felt252, amount: u256) {\n // L1 message handler\n }\n}\n\n// Common patterns\nfelt252, u128, u256\nContractAddress, EthAddress\n#[external(v0)], #[l1_handler], #[constructor]\nget_caller_address(), get_contract_address()\nsend_message_to_l1_syscall\nsrc/contract.cairo - Main contract implementationsrc/lib.cairo - Library modulestests/ - Contract testsScarb.toml - Cairo project configurationcargo install --git https://github.com/crytic/caracal --profile release --force (a Rust tool — not on PyPI)caracal detect src/When invoked, I will:
\nWhen vulnerabilities are found, you'll get a report like this:
\n=== CAIRO/STARKNET VULNERABILITY SCAN RESULTS ===\nI check for 6 critical vulnerability patterns unique to Cairo/Starknet. For detailed detection patterns, code examples, mitigations, and testing strategies, see VULNERABILITY_PATTERNS.md.
\nfelt252 wraps silently; use u128/u256For complete vulnerability patterns with code examples, see VULNERABILITY_PATTERNS.md.
\nsrc/*.cairo)# Find felt252 usage in arithmetic\nrg \"felt252\" src/ | rg \"[-+*/]\"\n\n# Find balance/amount storage using felt252\nrg \"felt252\" src/ | rg \"balance|amount|total|supply\"\n\n# Should prefer u128, u256 instead\nFor each #[l1_handler] function:
from_address parameterFor signature-based functions:
\nIf contract includes bridge functionality:
\n# Run Caracal detectors\ncaracal detect src/\n\n# Specific detectors\ncaracal detect src/ --detectors unchecked-felt252-arithmetic\ncaracal detect src/ --detectors unchecked-l1-handler-from\ncaracal detect src/ --detectors missing-nonce-validation\nReport on every pattern in §6, whether or not it turned anything up. Emit this table above the findings, with\nall 6 rows present:
\n| # | \nPattern | \nVerdict | \nEvidence | \n
|---|---|---|---|
| 1 | \nFelt252 Arithmetic Overflow/Underflow | \nclear | \nbalances are u256; searched felt252 in arithmetic, none | \n
| 2 | \nL1 to L2 Address Conversion | \n\n | \n |
| 3 | \nL1 to L2 Message Failure | \n\n | \n |
| 4 | \nOverconstrained L1 <-> L2 Interaction | \n\n | \n |
| 5 | \nSignature Replay Protection | \n\n | \n |
| 6 | \nUnchecked from_address in L1 Handler | \n\n | \n |
Each verdict is one of:
\nfound — cite file:line and write the finding up in full below.clear — the pattern applies to this contract and the contract handles it. Name the function, trait, or\ncheck you searched for, so a reader can repeat the search.n/a — the pattern cannot apply here. Give the reason in one clause (\"no L1 handlers in this contract\").\nNot having looked is not n/a.A table with fewer than 6 rows is an incomplete scan and must be reported as one. A row whose Verdict cell is empty is incomplete in the same way: row 1 above is filled in to show the shape, and every row is filled in the same way before the report is done. Six clear verdicts is a\nresult a reader can act on. A report that covers two patterns and says nothing about the other four reads\nexactly like a clean contract, and that is the failure this table exists to prevent.
## [CRITICAL] Unchecked from_address in L1 Handler\n\n**Location**: `src/bridge.cairo:145-155` (handle_deposit function)\n\n**Description**:\nThe `handle_deposit` L1 handler function does not validate the `from_address` parameter. Any L1 contract can send messages to this function and mint tokens for arbitrary users, bypassing the intended L1 bridge access controls.\n\n**Vulnerable Code**:\n```rust\n// bridge.cairo, line 145\n#[l1_handler]\nfn handle_deposit(\n ref self: ContractState,\n from_address: felt252, // Not validated!\n user: ContractAddress,\n amount: u256\n) {\n let current_balance = self.balances.read(user);\n self.balances.write(user, current_balance + amount);\n}\n```\n\n**Attack Scenario**:\n1. Attacker deploys malicious L1 contract\n2. Malicious contract calls `starknetCore.sendMessageToL2(l2Contract, selector, [attacker_address, 1000000])`\n3. L2 handler processes message without checking sender\n4. Attacker receives 1,000,000 tokens without depositing any funds\n5. Protocol suffers infinite mint vulnerability\n\n**Recommendation**:\nValidate `from_address` against authorized L1 bridge:\n```rust\n#[l1_handler]\nfn handle_deposit(\n ref self: ContractState,\n from_address: felt252,\n user: ContractAddress,\n amount: u256\n) {\n // Validate L1 sender\n let authorized_l1_bridge = self.l1_bridge_address.read();\n assert(from_address == authorized_l1_bridge, 'Unauthorized L1 sender');\n\n let current_balance = self.balances.read(user);\n self.balances.write(user, current_balance + amount);\n}\n```\n\n**References**:\n- building-secure-contracts/not-so-smart-contracts/cairo/unchecked_l1_handler_from\n- Caracal detector: `unchecked-l1-handler-from`\n#[cfg(test)]\nmod tests {\n use super::*;\n\n #[test]\n fn test_felt252_overflow() {\n // Test arithmetic edge cases\n }\n\n #[test]\n #[should_panic]\n fn test_unauthorized_l1_handler() {\n // Wrong from_address should fail\n }\n\n #[test]\n fn test_signature_replay_protection() {\n // Same signature twice should fail\n }\n}\n// Test full L1-L2 flow\n#[test]\nfn test_deposit_withdraw_roundtrip() {\n // 1. Deposit on L1\n // 2. Wait for L2 processing\n // 3. Verify L2 balance\n // 4. Withdraw to L1\n // 5. Verify L1 balance restored\n}\n# .github/workflows/security.yml\n- name: Run Caracal\n run: |\n # Rebuilds from source each run; cache ~/.cargo or pin a release binary instead.\n cargo install --git https://github.com/crytic/caracal --profile release --force\n caracal detect src/ --fail-on high,critical\nbuilding-secure-contracts/not-so-smart-contracts/cairo/Before completing Cairo/StarkNet audit:
\nArithmetic Safety (HIGH):
\nL1 Handler Security (CRITICAL):
\n#[l1_handler] functions validate from_addressL1-L2 Messaging (HIGH):
\nSignature Security (HIGH):
\nTool Usage:
\nfound, clear or n/a with a reasonn/a costs one\nclause and makes the judgment reviewable. Silence records nothing, and a reader cannot tell it apart from\nnot having checked.felt252 does not behave\nlike the sized integer types, and the boundary between them is where pattern 4 lives.from_address is the canonical StarkNet bridge bug.