[Security][tentative] Medium (correctness): SSZ State Root Omits Pending Execution Requests

[evonide]

Context

Summit's execution layer sends consensus-affecting requests such as deposits, withdrawals, and exits into finalizer state. Requests that must be deferred across a boundary are stored in pending_execution_requests and replayed later so future validator balances and statuses reflect earlier execution activity.

The SSZ state tree supplies the advertised state root used in finalized aux data and proof flows. For that root to bind consensus state, it must cover deferred execution work as well as immediately applied account and committee fields.

Claim

The SSZ state root omits pending_execution_requests even though deferred deposits, withdrawals, and exits are serialized consensus state that affect future transitions.

An honest block transition buffers deferred execution work in pending_execution_requests; the serialized state then differs in deferred deposits, withdrawals, or exits while SszStateTree omits that field, so the advertised SSZ state root and proofs remain unchanged.

Flow

The live start condition is narrower than any execution-request processing: parse_execution_requests first drains existing pending requests with take_pending_execution_requests, then later code can buffer a request such as a last-block active-validator withdrawal with push_pending_execution_request before capture_state_root. The prerequisite is a captured or rebuilt state that contains deferred request bytes; ordinary request replay that leaves the pending vector empty does not demonstrate this issue.

Impact

The parent_beacon_block_root and generated SSZ proofs do not commit to all consensus-relevant state. Checkpoint/restart/proof consumers can agree on a state root while disagreeing about deferred execution requests that schedule future deposits, withdrawals, or exits. That breaks the root-binds-state property expected from finalized roots and checkpoint proofs.

Root Cause

pending_execution_requests were added to serialized consensus state and transition logic but not added as a leaf/input to SszStateTree root construction.

Code

• ConsensusState stores pending_execution_requests: https://github.com/SeismicSystems/summit/blob/ed2c5c8/types/src/consensus_state.rs#L33.
• Live execution mutates pending execution requests: https://github.com/SeismicSystems/summit/blob/ed2c5c8/types/src/consensus_state.rs#L388, https://github.com/SeismicSystems/summit/blob/ed2c5c8/finalizer/src/actor.rs#L1473, https://github.com/SeismicSystems/summit/blob/ed2c5c8/finalizer/src/actor.rs#L1664.
• Pending execution requests are serialized/deserialized with consensus state: https://github.com/SeismicSystems/summit/blob/ed2c5c8/types/src/consensus_state.rs#L818, https://github.com/SeismicSystems/summit/blob/ed2c5c8/types/src/consensus_state.rs#L904, https://github.com/SeismicSystems/summit/blob/ed2c5c8/types/src/consensus_state.rs#L1045.
• Checkpoint docs describe pending execution requests as checkpoint content: https://github.com/SeismicSystems/summit/blob/ed2c5c8/docs/checkpointing.md#L36.
• SszStateTree defines a fixed top-level tree with no leaf for pending_execution_requests: https://github.com/SeismicSystems/summit/blob/ed2c5c8/types/src/ssz_state_tree.rs#L30, https://github.com/SeismicSystems/summit/blob/ed2c5c8/types/src/ssz_state_tree.rs#L55.
• Full SSZ tree rebuild accepts many consensus fields but has no pending-execution-request parameter: https://github.com/SeismicSystems/summit/blob/ed2c5c8/types/src/ssz_state_tree.rs#L874.
• ConsensusState::rebuild_ssz_tree likewise passes no pending execution requests: https://github.com/SeismicSystems/summit/blob/ed2c5c8/types/src/consensus_state.rs#L753.
• The root used in aux data comes from that tree: https://github.com/SeismicSystems/summit/blob/ed2c5c8/types/src/consensus_state.rs#L472, https://github.com/SeismicSystems/summit/blob/ed2c5c8/finalizer/src/actor.rs#L975, https://github.com/SeismicSystems/summit/blob/ed2c5c8/application/src/actor.rs#L649.

Related Issues/PRs

Related issues cover adjacent deferred execution request, epoch-boundary, and SSZ root omissions that can leave future state unbound.

• [Security][tentative] Medium (correctness): Epoch Transition Root Is Captured Before Boundary Mutations #243
• [Security][tentative] Medium (attackable): Last-Block Withdrawal Can Be Dropped By Same-Block Deposit #248
• [Security][tentative] Medium (attackable): SSZ State Root Omits Dynamic Epoch Schedule #256
• [Security][tentative] Medium (attackable): SSZ State Root Omits Keyed Collection Keys #257
• [Security][tentative] Medium (attackable): SSZ State Root Omits Pending Checkpoint #258
• [Security][tentative] Medium (correctness): State-Proof Batches Drop Missing Keys #260
• [Security][tentative] Medium (attackable): Typed Finalized Headers Can Bypass Signed Field Binding #261

Fix

• Add pending_execution_requests to the SSZ state tree with a stable merkleization format.
• Rebuild roots from every consensus field that can affect future state transitions.
• Add a test that changes only pending_execution_requests and asserts the state root changes.
• Version checkpoint/state-root format if existing roots cannot be made backward compatible.