Frontier opcode SUICIDE touches too many storage values on large contracts

Vulnerability

In the Frontier Ethereum compatibility layer for Substrate, prior to commit aea528198b3b226e0d20cce878551fd4c0e3d5d0, the SUICIDE opcode (also known as SELFDESTRUCT) at the end of a contract execution uses storage::remove_prefix (later renamed storage::clear_prefix) to remove all storage entries associated with the contract being deleted. This is performed in a single IO primitive call crossing the WebAssembly boundary [1][3]. For contracts with many storage values, this operation can be slow and, critically for parachains, all deleted storage items become part of the Proof-of-Validation (PoV) block. The maintainers charge only a fixed cost for SUICIDE, regardless of the number of storage entries [3]. No limit parameter is supplied to the storage clear call, so it removes all storage in one batch [1].

Exploitation

An attacker can craft a contract that writes a very large number of storage key-value pairs and then calls the SUICIDE opcode. On a parachain, if the transaction containing this SUICIDE call is included in a block, the PoV size will exceed the relay chain's PoV size limit, causing the parachain to stall because the block cannot be validated by the relay chain [3]. The attacker only needs the ability to deploy and execute contracts on the parachain; no special privileges are required. XCM transactions that reference such a contract cannot be skipped, making the issue particularly impactful for cross-chain messages [3].

Impact

Successful exploitation leads to a denial-of-service condition: the parachain stalls because the relay chain rejects PoV blocks that exceed the size limit. This prevents new blocks from being produced on the parachain, halting all activity until the network recovers. For parachains, the severity is high. On standalone chains, the impact is reduced because there is no relay chain PoV limit, but the unbounded storage clear call may still cause a slowdown [3].

Mitigation

The fix is implemented in commit aea528198b3b226e0d20cce878551fd4c0e3d5d0 (PR #1212) [1][2]. The patch introduces asynchronous suiciding by marking accounts as Suicided and deferring the actual storage deletion, avoiding an unbounded single call [2]. For parachains, an emergency runtime upgrade is recommended as soon as possible. For standalone chains, a normal runtime upgrade is advised. As of the advisory publication (October 2023), no known workarounds exist [3]. The vulnerability is not listed on CISA's KEV catalog as of the publication date.