🛡️ Sentinel: [CRITICAL] Total State Root Divergence (Consensus Fork) via OnStateHook Side-Effect Leakage in Block Execution Validations

[HeshamASH]

Found a critical vulnerability where ArcBlockExecutor leaks state mutations to the consensus engine via OnStateHook before the block has fully completed validation. If an invalid block is dropped, the node still incorporates these leaked state changes into its global trie tracker, causing a permanent state root divergence between nodes that evaluate the block and nodes that do not. Included a PoC test in executor.rs to demonstrate the vulnerability along with a comprehensive Report.md and a .jules/sentinel.md journal entry.

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PR created automatically by Jules for task 12534065350538320716 started by @HeshamASH

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[qodo-code-review]

Review Summary by Qodo

Fix critical state root divergence via OnStateHook side-effect leakage

🐞 Bug fix 🧪 Tests

Walkthroughs

Description

• Identifies critical state root divergence vulnerability in block execution
• OnStateHook emits state changes before validation completes, causing consensus fork
• Adds PoC test demonstrating pre-execution state leakage via beneficiary validation
• Includes comprehensive vulnerability report with CVSS 10.0 severity assessment

Diagram

flowchart LR
  A["Block Validation Start"] --> B["apply_blockhashes_contract_call"]
  B --> C["OnStateHook emits state"]
  C --> D["Beneficiary validation"]
  D -->|Fails| E["Block aborted"]
  E --> F["State already leaked to consensus"]
  F --> G["Permanent state root divergence"]

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File Changes

1. crates/evm/src/executor.rs 🧪 Tests +63/-0

Add PoC test for state root divergence vulnerability

• Added MockHook struct to simulate OnStateHook behavior in tests
• Implemented test_state_root_divergence_poc() test demonstrating the vulnerability
• Test creates a block with wrong beneficiary to trigger validation failure
• Verifies that OnStateHook is called before validation completes, proving state leakage

crates/evm/src/executor.rs

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2. Report.md 📝 Documentation +118/-0

Detailed security report on state root divergence vulnerability

• Comprehensive vulnerability analysis with detailed technical explanation
• Documents two state leakage points: pre-execution (apply_pre_execution_changes) and
 post-execution (finish)
• Includes executable PoC code demonstrating the vulnerability
• Provides CVSS 4.0 assessment with severity score of 10.0 (Critical)
• Recommends remediation: move all validations before state-modifying operations

Report.md

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3. .jules/sentinel.md 📝 Documentation +4/-0

Sentinel journal entry for state leakage vulnerability

• Journal entry documenting the vulnerability discovery date and details
• Explains the core issue: state leaks to consensus layer are unrecoverable
• Highlights learning: validation nodes retain corrupted state root causing permanent
 non-determinism
• Suggests prevention: execute all block-level validations before first state-modifying instruction

.jules/sentinel.md

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[qodo-code-review]

Code Review by Qodo

🐞 Bugs (0) 📘 Rule violations (0) 📎 Requirement gaps (0)

1. PoC asserts vulnerability ☑ 🐞 Bug ⚙ Maintainability

Description

test_state_root_divergence_poc asserts OnStateHook was called even though
apply_pre_execution_changes() returned an error, thereby encoding the insecure behavior as the
expected outcome. This will either block the eventual fix (test will fail once the hook leakage is
prevented) or mislead the test suite into validating an unsafe invariant.

Code

crates/evm/src/executor.rs[R1163-1171]

+        // This fails validation and aborts block execution
+        let result = executor.apply_pre_execution_changes();
+        assert!(result.is_err(), "Beneficiary validation should fail");
+
+        let was_called = *hook_called.lock().unwrap();
+        assert!(
+            was_called,
+            "CRITICAL VULNERABILITY: OnStateHook was called and emitted state mutations to the consensus engine BEFORE the block validation failed and aborted. This causes permanent state root divergence between nodes!"
+        );

Evidence

The new PoC explicitly expects apply_pre_execution_changes() to error and then asserts the hook
was called (assert!(was_called, ...)), meaning the test passes only while the leakage exists and
will fail once corrected.

crates/evm/src/executor.rs[1111-1172]

Agent prompt

The issue below was found during a code review. Follow the provided context and guidance below and implement a solution

## Issue description
The added PoC test currently asserts the vulnerable behavior (hook called before block validation failure), which makes it unsuitable as a long-lived regression test and will break once the vulnerability is fixed.
### Issue Context
This PR appears to document/reproduce the issue. To avoid coupling CI to an insecure property, the PoC should either be excluded from default test runs or rewritten to assert the *desired* post-fix behavior.
### Fix Focus Areas
- crates/evm/src/executor.rs[1111-1172]
### Suggested changes
- Option A (preferred until fix lands): mark `test_state_root_divergence_poc` as `#[ignore]` (and optionally add a short comment explaining it’s a reproduction test).
- Option B (when fix lands): invert the assertion to `assert!(!was_called, ...)` (or assert the hook receives no state changes until validations pass), and rename to a regression-style name (e.g., `test_no_hook_emission_on_validation_error`).

ⓘ Copy this prompt and use it to remediate the issue with your preferred AI generation tools

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2. Exploit details in repo ☑ 🐞 Bug ⛨ Security

Description

This PR adds Report.md (and a .jules journal entry) containing detailed exploit mechanics, code
snippets, and a ready-to-run reproduction for a critical consensus-fork vulnerability. Publishing
this content in the main repo materially lowers the effort needed to weaponize the issue for anyone
with repo access prior to coordinated rollout of a fix.

Code

Report.md[R1-42]

+# 🛡️ Sentinel: [CRITICAL] Total State Root Divergence (Consensus Fork) via OnStateHook Side-Effect Leakage in Block Execution Validations
+
+## Summary
+The Arc Network's EVM executor incorrectly sequences block validation logic *after* emitting state changes to the consensus layer's `OnStateHook`. Both `ArcBlockExecutor::apply_pre_execution_changes()` and `ArcBlockExecutor::finish()` execute operations that commit and emit state changes to the node's global trie tracker (`hook.on_state`), but subsequently perform critical block validations that can return a `BlockExecutionError` and abort the block.
+
+When a block is aborted due to a validation failure, the execution context is dropped and the block is discarded by the local node. **However, the `OnStateHook` side-effects have already been emitted and irreversibly incorporated into the node's state root.**
+
+If a malicious validator proposes a block designed to fail these late-stage validations, nodes that attempt to validate the block will permanently corrupt their state root with the partial block execution, while nodes that immediately reject the block (or build a different block) will not. This causes an unrecoverable consensus split (network fork) on the very next successful block.
+
+## Vulnerability Details
+
+The execution of a block is a state transition function: `STF(State, Block) -> State'`. If a block is invalid, `STF` should return an error and the node's state must remain `State`. In Arc, the consensus boundary relies on `OnStateHook::on_state` to stream the incremental state changes of a block to the consensus engine (Malachite/Reth) to compute the new state root.
+
+### 1. The Pre-Execution Leak (`apply_pre_execution_changes`)
+In `apply_pre_execution_changes()`, the executor first calls `apply_blockhashes_contract_call()`, which executes the EIP-2935 system call and explicitly triggers `hook.on_state`:
+```rust
+// In alloy_evm::block::system_calls::apply_blockhashes_contract_call
+if let Some(hook) = &mut self.hook {
+    hook.on_state(StateChangeSource::PreBlock(StateChangePreBlockSource::BlockHashesContract), &res.state);
+}
+evm.db_mut().commit(res.state);
+```
+Immediately *after* this state is emitted, `apply_pre_execution_changes` performs multiple critical validations:
+```rust
+// 1. Validates the block beneficiary
+validate_expected_beneficiary(header_beneficiary, expected_beneficiary, block_number)?;
+// 2. Validates the beneficiary is not blocklisted
+validate_beneficiary_not_blocklisted(self.evm.db_mut(), header_beneficiary, block_number)?;
+// 3. Validates the block gas limit
+if block_gas_limit != expected { return Err(...); }
+```
+If any of these fail, the block is aborted. But the EIP-2935 storage mutation has already been streamed to the consensus state hook!
+
+### 2. The Post-Execution Leak (`finish`)
+Similarly, in `ArcBlockExecutor::finish()`, after all transactions have been executed and their state changes emitted via `hook.on_state`, a final validation is performed on the `extra_data`:
+```rust
+if is_zero5 && !self.ctx.extra_data.is_empty() {
+    self.validate_extra_data_base_fee(block_number, gas_values.nextBaseFee)?;
+}
+```
+If the block proposer forged an invalid `nextBaseFee` in the `extra_data`, this validation fails and the block aborts. However, the state changes from *every single transaction in the block* have already been emitted to the consensus hook!
+

Evidence

Report.md includes step-by-step vulnerability details, code snippets identifying the leaking call
site and late validations, and an explicit PoC description; .jules/sentinel.md also summarizes the
issue. Keeping this in-repo means it is distributed to all repo consumers immediately upon merge.

Report.md[1-92]
.jules/sentinel.md[1-4]

Agent prompt

The issue below was found during a code review. Follow the provided context and guidance below and implement a solution

## Issue description
The PR adds detailed exploit documentation for a critical consensus vulnerability directly into the repository, which can accelerate exploitation for anyone with access before a fix is fully deployed.
### Issue Context
Even if the repo is private, merge propagation often widens access (mirrors, forks, CI artifacts). If this is intended for internal security tracking, consider moving it to a restricted channel/repo or landing it only after the fix is shipped.
### Fix Focus Areas
- Report.md[1-118]
- .jules/sentinel.md[1-4]
### Suggested changes
- Move `Report.md` (and/or `.jules/sentinel.md`) to a private security/advisory repository or internal doc system.
- If it must remain in-tree, redact weaponizable details (exact code snippets/steps) and add a clear note about disclosure timing (e.g., "Do not merge until fix deployed" / "Fixed in <version/commit>").

ⓘ Copy this prompt and use it to remediate the issue with your preferred AI generation tools

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