The Arbitrum Security Council has temporarily disabled new Stylus contract activations on Arbitrum One and Arbitrum Nova as a precaution against emerging WebAssembly attack techniques. According to Arbitrum’s official security notice, the restriction took effect on October 2 and prevents new or expired Stylus programs from being activated. No attack has occurred and Arbitrum says no user funds have been affected by the Stylus vulnerabilities identified to date.
The emergency action responds to increasingly sophisticated AI-assisted tooling capable of producing hand-crafted WASM programs outside the standard Stylus compiler workflow. Arbitrum says such programs can deliberately trigger unexpected execution behavior and degrade network performance. The known Stylus bugs primarily threaten chain liveness through denial-of-service-style behavior rather than enabling attackers to steal assets. Existing applications therefore remain operational while the Foundation and ArbitrumDAO evaluate how to reopen activation safely.
Existing Stylus Contracts Continue Running
The restriction applies specifically to Stylus activation, the process that compiles and prepares WASM programs to become callable on Arbitrum. The Security Council raised the configurable activation gas requirement to the maximum uint64 value, making new activations prohibitively expensive without disabling Stylus execution itself. Already-active contracts can still execute normally, while Solidity and other EVM contracts are completely unaffected by the measure.
Developers can also continue renewing an active Stylus program through the permissionless keepalive mechanism before it expires. However, an expired contract cannot currently be reactivated, and an application requiring fresh activation after a Stylus version change cannot deploy that update. ArbOS 61 renewed all active programs on Arbitrum One, meaning currently active contracts there will not expire before August 20, 2027.
The pause temporarily narrows a development environment that Arbitrum has been actively promoting. Builders participating in the recent Open House Singapore program could deploy applications using either Solidity or Stylus-compatible languages, including Rust and other languages compiled to WASM. The emergency configuration affects future Stylus activations on One and Nova, not the broader ability to build or execute EVM applications across the Arbitrum ecosystem.
Separate Guard Can Pause Ethereum Settlement
The October 2 Security Council action also introduced a second safeguard unrelated to Stylus. Arbitrum One now has a permissionless One-Step Proof soundness guard that can pause settlement to Ethereum if two conflicting answers to the same challenge step are both accepted when only one should be valid. If triggered, Arbitrum One would continue processing transactions, but unconfirmed messages from Arbitrum to Ethereum, including withdrawals, would wait until the issue was resolved.
That mechanism addresses a different security boundary from the WASM activation pause. The Stylus action limits the introduction of potentially hostile programs, while the OSP guard protects the validity-proof process governing settlement to Ethereum. Neither safeguard represents a general shutdown of Arbitrum One or Nova. The distinction resembles other infrastructure incidents where a flaw in a specific execution component must be separated from the security of the underlying network, as seen when Cosmos EVM chains were advised to halt during an upstream module security incident.
Emergency intervention also illustrates the role governance retains in Layer 2 infrastructure. ARB itself primarily provides governance rights rather than a direct claim on network revenue, with holders able to influence upgrades and other ecosystem decisions through the DAO, a distinction relevant to the broader relationship between Layer 2 networks and their governance tokens. In this case, the Security Council exercised its emergency authority first, while the Foundation says it will work with ArbitrumDAO on the conditions and timing for restoring Stylus activations.
No reopening date has been announced. The immediate state of the network is therefore deliberately asymmetric: existing Stylus applications remain usable, EVM development continues normally, but introducing fresh Stylus bytecode on Arbitrum One or Nova is blocked until the ecosystem establishes a safer path for handling hand-crafted WASM.