Arbitrum’s Security Council executed an emergency upgrade on Arbitrum One and Nova at 11:30 a.m. Eastern Time on Oct. 2, pausing all new Stylus contract activations on both chains and adding a safeguard for BoLD one-step proofs in Arbitrum One’s dispute system.
Upgrade covers Stylus and BoLD protections
The Arbitrum Foundation said the action is part of an ongoing proactive security measure designed to protect the network’s security and integrity.
Stylus allows developers to write smart contracts in languages including Rust and C++ while keeping compatibility with the Ethereum Virtual Machine. Those programs are compiled into WebAssembly format.
According to the announcement, the pause mainly targets manually written WASM programs that did not use the standard Stylus compiler toolchain and have not been patched by the current version of ArbOS. The Security Council raised the gas required for activation to its theoretical maximum by calling ArbOwner.setWasmActivationGas(2^64 - 1), making new activations economically impractical.
Existing contracts continue to run
Already activated Stylus contracts are not affected and can continue to execute and renew. Deployment and execution of Solidity contracts also remain unaffected.
New safeguard added to Arbitrum One dispute system
The added BoLD protection allows anyone to pause settlement from Arbitrum One to Ethereum if two conflicting answers are both accepted at the same dispute step.
The Foundation said unconfirmed withdrawals may be delayed as a result, giving the Security Council time to deploy a fix.
Foundation says known issue affects liveness, not funds
Arbitrum said the Stylus-related vulnerability identified so far mainly affects chain liveness, including denial-of-service scenarios, and does not endanger user funds.