Arbitrum Strengthens Network Security with Emergency Pause on Stylus Activations

In a proactive move to safeguard the ecosystem, the Arbitrum Security Council has implemented an emergency restriction on new Stylus contract activations across the Arbitrum One and Nova networks. Triggered on October 2, this measure serves as a defensive shield against increasingly sophisticated AI-assisted attacks that leverage hand-crafted WebAssembly programs. While existing applications continue to function normally, the pause underscores the network's commitment to maintaining operational integrity in the face of evolving digital threats.

Addressing the Threat of AI-Assisted Attacks

The decision to restrict activations stems from the discovery of potential vulnerabilities that could compromise chain liveness. Specifically, Arbitrum identified risks associated with denial-of-service (DoS) attacks orchestrated through non-standard WebAssembly programs created outside the official Stylus compiler toolchain. Importantly, the Security Council clarified that these bugs do not pose a threat to user funds, as no exploits allowing for theft have been discovered. By raising the activation gas requirement to prohibitively expensive levels, the Council has effectively paused the onboarding of new executable code without requiring a full upgrade to the ArbOS software.

Impact on Developers and Contract Deployment

For builders within the Arbitrum ecosystem, the distinction between storing code and making it executable is now critical. While new Stylus contracts can still be deployed to the blockchain, they cannot be "activated" to become runnable during this period. However, the restriction is surgical in nature: existing programs remain callable, and developers can still use the permissionless keepalive mechanism to extend the lifetime of currently active programs. Standard Solidity contract deployments and executions remain entirely unaffected, ensuring that the vast majority of network activity continues without interruption.

Settlement Safeguards and Future Outlook

Parallel to the Stylus restrictions, the Council also introduced a safeguard for BoLD (Bounded Liquidity Delay) one-step proofs on Arbitrum One. This mechanism is designed to pause settlements to the Ethereum mainnet if conflicting answers are presented during an open challenge, a move that could temporarily delay withdrawals but prevents incorrect state transitions. As of now, there is no specific timeline for the restoration of Stylus activations. The Arbitrum Foundation is expected to collaborate with the ArbitrumDAO to determine the safest path forward for reopening these features once comprehensive fixes are deployed.