Cairo Smart Contract
Security

Starknet changes accounts, messages, upgrades, and math. Learn the Cairo audit checks before your Solidity instincts miss the bug.

Contract accounts L1-L2 handlers Class hash upgrades
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JohnnyTime Guide by JohnnyTime
Cairo language logo artwork
A different VM needs different review habits.
Starknet
Message Flow

Validate L1 source, replay rules, and failed messages.

Cairo Audit Note
check __validate__
trace l1_handler
review class_hash
test felt252 bounds

Cairo auditing is a
different review surface.

Your EVM instincts still help. These are the places where they need backup.

Contract accounts
  • Validate signatures
  • Check nonce flow
  • Review custom wallet logic
Async messages
  • Verify L1 source
  • Map replay paths
  • Handle failed messages
Cairo types
  • Trace felt252 assumptions
  • Check u256 conversions
  • Review bounds and division

Review Cairo contracts
in the right order.

Model authority first. Then messages, upgrades, and numeric assumptions.

1

Account model

  • Check __validate__
  • Review signer assumptions
  • Trace nonce handling
2

Cross-layer messages

  • Validate l1_handler source
  • Map replay and cancellation
  • Test failed bridge states
3

Upgrade surface

  • Protect class hash changes
  • Review initializer state
  • Trace admin recovery paths
4

Numeric assumptions

  • Check felt252 and u256
  • Review rounding and division
  • Test boundary values

Choose the right Cairo
security next step.

Use the course for labs, the guide for a map, and EVM practice when the basics need sharpening.

Cairo Smart Contract Hacking Course
  • Hands-on Cairo labs
  • Starknet-specific bugs
Start training
Cairo & Starknet Audit Guide
  • Account abstraction map
  • L1-L2 review checklist
Read the guide
Smart Contract Hacking Course
  • Audit workflow practice
  • PoCs and report writing
View the EVM course
Smart Contract Attack Classes
  • Bug class refreshers
  • Security mental models
Browse attack classes

Build Starknet
security judgment.

Practice Cairo-specific review habits: accounts, messages, upgrades, and proof-driven findings.

Hands-on labs Cairo attack surfaces Auditor workflow
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