CryptoSlate
Arbitrum's Security Council temporarily blocked new Stylus contract activations on Arbitrum One and Nova in an October 2 emergency action. The council cited increasingly sophisticated AI-assisted attacks using hand-crafted WebAssembly programs outside the standard Stylus compiler toolchain. It said known bugs primarily threaten chain liveness, including through denial of service, and that it has found no attack permitting theft of user funds.
Why it matters
Stylus activation makes a deployed WebAssembly program executable. During the pause, developers can still store code onchain, but a new application version that needs fresh activation cannot run. New contract instances can reuse an existing valid activation for identical code. Already-active Stylus applications remain callable, and ordinary Solidity deployment and execution are unaffected.
The restriction also blocks reactivation of expired programs and programs requiring reactivation after a Stylus version change. Developers can use the permissionless keepalive mechanism to extend an active program's lifetime before it expires. The council implemented the pause by raising the activation gas requirement to a prohibitively expensive level, without an ArbOS upgrade.
Market impact
A separate safeguard added in the same emergency action could delay settlement from Arbitrum One to Ethereum if BoLD's one-step proof accepts two conflicting answers to the same challenge step. One would continue processing, but unconfirmed messages to Ethereum, including withdrawals, would wait for a fix. Installing the guard did not itself pause withdrawals.
For Arbitrum builders, the immediate constraint is on launching or updating Stylus code that needs activation, not on every contract deployment. The Foundation will work with ArbitrumDAO on how and when to restore activations; no reopening date was given.
Frequently asked questions
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Can existing Stylus applications continue running on Arbitrum?
Yes. Already-active Stylus programs remain callable until expiration, and developers can extend an active program's lifetime through the keepalive renewal mechanism.
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Can developers deploy new Stylus code during the pause?
They can store code onchain, but a program requiring fresh activation cannot become executable. New instances using identical code can reuse an existing valid activation.
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What risks prompted the Stylus activation pause?
Arbitrum cited increasingly sophisticated AI-assisted attacks involving hand-crafted WebAssembly programs. It said known bugs primarily threaten chain liveness and that no attack permitting theft of user funds had been discovered.
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Are Arbitrum One withdrawals to Ethereum paused?
No. A separate safeguard would delay unconfirmed messages, including withdrawals, only if a one-step proof accepted two conflicting answers to the same challenge step.
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When will new Stylus activations resume?
No date was given. The Arbitrum Foundation will work with ArbitrumDAO on the timeline and manner of restoring activations.
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