code-423n4 / 2023-05-base

Base audit details

• Total Prize Pool: $100,000 USDC
  • HM awards: $74,619 USDC
  • QA report awards: $8,291 USDC
  • Gas report awards: $0 USDC
  • Judge awards: $9,950 USDC
  • Lookout awards: $6,640 USDC
  • Scout awards: $500 USDC
• Join C4 Discord to register
• Submit findings using the C4 form
• Read our guidelines for more details
• Starts May 26, 2023 20:00 UTC
• Ends June 09, 2023 20:00 UTC

IMPORTANT NOTE: Prior to receiving payment from this audit you MUST become a Certified Warden (successfully complete KYC). You do not have to complete this process before competing or submitting bugs. You must have started this process within 48 hours after the audit ends, i.e. by June 11, 2023 at 20:00 UTC in order to receive payment.

Overview

Base is a secure, low-cost, developer-friendly Ethereum L2 built to bring the next billion users on-chain. It is built on the MIT-licensed OP Stack, in collaboration with Optimism. Coinbase is joining as the second Core Dev team working on the OP Stack to ensure it’s a public good available to everyone.

Scope

The key components within the scope of the contest include:

• L1 Contracts

• L2 Contracts

• op-node

• op-geth

We encourage participants to look for bugs in the following areas:

• Node vulnerabilities
• EVM equivalence vulnerabilities
• Bridge vulnerabilities
• Generic smart contract issues

External repos

We are basing this contest on OP-monorepo and op-geth.

These commit hashes will be considered as a code freeze for the purposes of this contest.

These repos were added as submodules to the contest's repo. To fetch them, please clone with git clone --recurse-submodules or run git submodule update --init --recursive if you haven't cloned with submodules.

You can see these contracts deployed on testnet here : https://docs.base.org/network-information

Contracts Overview

Contracts deployed to L1

Name	Proxy Type	Description
L1CrossDomainMessenger	ResolvedDelegateProxy	High-level interface for sending messages to and receiving messages from Optimism
L1StandardBridge	L1ChugSplashProxy	Standardized system for transfering ERC20 tokens to/from Optimism
L2OutputOracle	Proxy	Stores commitments to the state of Optimism which can be used by contracts on L1 to access L2 state
OptimismPortal	Proxy	Low-level message passing interface
OptimismMintableERC20Factory	Proxy	Deploys standard OptimismMintableERC20 tokens that are compatible with either StandardBridge
SystemConfig	Proxy	Store system config on L1 and picked up by L2 as part of chain derivation
SystemDictator	Proxy	Helps with deployment of bedrock system.
ProxyAdmin	-	Contract that can upgrade L1 contracts

Contracts deployed to L2

Name	Proxy Type	Description
GasPriceOracle	Proxy	Stores L2 gas price configuration values
L1Block	Proxy	Stores L1 block context information (e.g., latest known L1 block hash)
L2CrossDomainMessenger	Proxy	High-level interface for sending messages to and receiving messages from L1
L2StandardBridge	Proxy	Standardized system for transferring ERC20 tokens to/from L1
L2ToL1MessagePasser	Proxy	Low-level message passing interface
SequencerFeeVault	Proxy	Vault for L2 transaction fees
OptimismMintableERC20Factory	Proxy	Deploys standard OptimismMintableERC20 tokens that are compatible with either StandardBridge
ProxyAdmin	-	Contract that can upgrade L2 contracts when sent a transaction from L1

Out of scope

Legacy and deprecated contracts

Name	Location	Proxy Type	Description
AddressManager	L1	-	Legacy upgrade mechanism (unused in Bedrock)
DeployerWhitelist	L2	Proxy	Legacy contract for managing allowed deployers (unused since EVM Equivalence upgrade)
L1BlockNumber	L2	Proxy	Legacy contract for accessing latest known L1 block number, replaced by L1Block

• Legacy code that doesn't affect bedrock.*

Roles

The following table outlines all the roles and their permissions in the system

Role	Capability
L2 ProxyAdmin Owner	Can instantly upgrade all L2 contracts.
L1 ProxyAdmin Owner	Can instantly upgrade all L1 contracts.
Challenger	Can call deleteL2Outputs() in the event of fault.
MSD Controller	Controls the Migration SystemDictator contract.
System Config Owner	Can modify system config values.
Proposer	Can propose new L2 Outputs.
Sequencer	Can submit new transaction batches.
Guardian	Can pause and unpause the Portal.

Previous audits

https://github.com/ethereum-optimism/optimism/tree/develop/technical-documents/security-reviews

https://github.com/sherlock-audit/2023-03-optimism-judging

https://github.com/sherlock-audit/2023-01-optimism-judging

Assumptions & Roadmap features

* Sequencer is centralized at the moment
* Users cannot propose L2 blocks at the moment
* No fault proofs at the moment
* Contracts are upgradable
* Proposer is assumed to always propose correct l2 values
* Challenger is assumed to challenge only in case of a fault
* Guardian is assumed to only pause if necessary, not for greifing other users
* Batcher  is assumed to always propose correct batches

Known Issues

*Previously known and documented risks will not be will not be accepted as valid findings. Please refer to previous audits, known issues, OP Spec and Assumptions and Roadmap features.

*There is an edge case in which ETH deposited to the OptimismPortal by a contract can be irrecoverably stranded:

When a deposit transaction fails to execute, the sender's account balance is still credited with the mint value. However, if the deposit's L1 sender is a contract, the tx.origin on L2 will be aliased, and this aliased address will receive the minted on L2. In general the contract on L1 will not be able to recover these funds.We have documented this risk and encourage users to take advantage of our CrossDomainMessenger contracts which provide additional safety measures.

*Deposit griefing by filling up the MAX_RESOURCE_LIMIT

This issue is mitigated by PR 5064, which does not completely resolve the issue but does increase the cost of a sustained griefing attack. A more complete fix will require architectural changes.

*There are various 'foot guns' in the bridge which may arise from misconfiguring a token. Examples include:

Having both (or neither of) the local and remote tokens be OptimismMintable. Tokens which dynamically alter the amount of a token held by an account, such as fee-on-transfer and rebasing tokens. To minimize complexity our bridge design does not try to prevent all forms of developer and user error.

*When running in non-archive mode op-geth has difficulty executing deep reorgs. We are working on a fix.

Build & Tests

Please refer to the below documentation for building the repo.

https://stack.optimism.io/docs/build/getting-started/

https://github.com/ethereum-optimism/optimism/blob/382d38b7d45bcbf73cb5e1e3f28cbd45d24e8a59/packages/contracts-bedrock