# GHSA-3whf-vgf2-9w6g: zaino-state has a Non-Finalized State Reorg — No Cycle Detection or Depth Limit

> A malicious validator can cause infinite recursion and CPU exhaustion in the Zaino state library by serving cyclic block data, leading to denial of service.

- **Severity:** Not scored
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 31 Jul 2026

## What is GHSA-3whf-vgf2-9w6g?

GHSA-3whf-vgf2-9w6g is a denial of service vulnerability in zaino-state, published on 31 Jul 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

### Summary
`NonFinalizedState::handle_reorg` is a recursive, unbounded async function that traverses parent blocks until it finds a common ancestor on the main chain. It has **no recursion depth limit** and **no cycle detection**. A malicious or buggy validator can serve a block whose `previous_block_hash` points back to itself (or forms a cycle with other blocks), causing `handle_reorg` to infinite-loop, consuming 100% CPU and never making sync progress. Additionally, `update()` contains an `.expect("empty snapshot impossible")` that panics if the non-finalized snapshot becomes empty after trimming finalized blocks.

### Details

**Location:** `packages/zaino-state/src/chain_index/non_finalised_state.rs:443-489`

```rust
async fn handle_reorg(
    &self,
    working_snapshot: &mut NonfinalizedBlockCacheSnapshot,
    block: &impl Block,
) -> Result<IndexedBlock, SyncError> {
    let prev_block = match working_snapshot
        .get_block_by_hash_bytes_in_serialized_order(block.prev_hash_bytes_serialized_order())
        .cloned()
    {
        Some(prev_block) => {
            if !working_snapshot
                .heights_to_hashes
                .values()
                .any(|hash| hash == prev_block.hash())
            {
                Box::pin(self.handle_reorg(working_snapshot, &prev_block)).await?  // <-- LINE 459
            } else {
                prev_block
            }
        }
        None => {
            let prev_block = self
                .source
                .get_block(HashOrHeight::Hash(
                    zebra_chain::block::Hash::from_bytes_in_serialized_order(
                        block.prev_hash_bytes_serialized_order(),
                    ),
                ))
                .await
                .map_err(|e| { ... })?
                .ok_or(SyncError::ValidatorConnectionError(...))?;
            Box::pin(self.handle_reorg(working_snapshot, &*prev_block)).await?  // <-- LINE 483
        }
    };
    let indexed_block = block.to_indexed_block(&prev_block, self).await?;
    working_snapshot.add_block_new_chaintip(indexed_block.clone());
    Ok(indexed_block)
}
```

**Infinite loop via self-referencing block:**
1. A compromised validator serves a block `B` where `B.prev_hash == B.hash`.
2. `handle_reorg` is called with `B`.
3. `get_block_by_hash_bytes_in_serialized_order(B.prev_hash)` finds `B` itself in `working_snapshot.blocks`.
4. Check: is `B.hash` in `working_snapshot.heights_to_hashes`? If `B` is a new chaintip not yet on the main chain, **no**.
5. Recurse with `prev_block` = `B` (the exact same block).
6. This repeats forever. The async recursion builds a new `Box::pin` future each iteration, consuming heap memory and CPU.

**Stack exhaustion via deep reorg:**
A deep reorg of >1000 blocks would recurse >1000 times. Each async recursion creates a new `Box::pin` future on the heap. While this won't exhaust the native stack immediately, it will allocate unbounded heap memory and CPU time, effectively DoS-ing the sync task.

**`.expect("empty snapshot impossible")` panic:**

**Location:** `packages/zaino-state/src/chain_index/non_finalised_state.rs:543-548`

```rust
new_snapshot.remove_finalized_blocks(finalized_height);
let best_block = &new_snapshot
    .blocks
    .values()
    .max_by_key(|block| block.chainwork())
    .cloned()
    .expect("empty snapshot impossible"); // <-- LINE 548
```

If `finalized_height` is greater than or equal to all blocks in `new_snapshot.blocks`, `remove_finalized_blocks` retains only blocks at or above that height. If none exist, `new_snapshot.blocks` becomes empty. The `.expect()` then panics. While the comment claims this is "impossible," defensive programming dictates it is reachable under corruption or edge-case sync conditions.

### PoC

1. Run a regtest.
2. Serve a block where `header.previous_block_hash == block.hash()`.
3. Zaino's `NonFinalizedState::sync` enters `handle_reorg` and infinite-loops.
4. Sync never completes. CPU usage pegs to 100%. No new blocks are served to clients.

### Fix

1. **Add an explicit recursion depth limit** (e.g., max 1000 iterations) and return `SyncError::ReorgFailure` if exceeded:
   ```rust
   const MAX_REORG_DEPTH: usize = 1000;
   ```
2. **Track visited hashes** in a `HashSet<BlockHash>` during traversal to detect cycles and abort with an error.
3. **Replace `.expect("empty snapshot impossible")`** with a proper `Err(UpdateError::DatabaseHole)` or similar error return.

### Additional Attack Vectors

- **Deep reorg DoS:** A miner with significant hash power (or a compromised validator) triggers a deep reorg. Zaino spends excessive CPU and memory in `handle_reorg`, starving the async runtime and stalling response serving.
- **Fork-choice manipulation:** By serving cyclic or very deep sidechains, an attacker can keep Zaino stuck in reorg handling indefinitely, preventing it from ever serving the real best chain.

## Which versions are affected by GHSA-3whf-vgf2-9w6g?

2 open source packages ship an affected version, including zaino-state.


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `zaino-state` | crates.io | All versions | 0.4.1 |
| `zaino-state` | crates.io | All versions | 0.4.1 |

## How do I fix GHSA-3whf-vgf2-9w6g?

Upgrade zaino-state to 0.4.1 or later.

## Is GHSA-3whf-vgf2-9w6g being exploited?

There is no known exploitation of GHSA-3whf-vgf2-9w6g in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for GHSA-3whf-vgf2-9w6g and fix it if it is affected.

What it is: GHSA-3whf-vgf2-9w6g is a denial of service vulnerability in zaino-state, published on 31 Jul 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: There is no known exploitation of GHSA-3whf-vgf2-9w6g in the wild and no public exploit code.

Affected packages and fixed versions:
- zaino-state (crates.io): affected all versions; fixed in 0.4.1
- zaino-state (crates.io): affected all versions; fixed in 0.4.1

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/GHSA-3whf-vgf2-9w6g/ (Markdown: https://insights.sbomify.com/GHSA-3whf-vgf2-9w6g/index.md)
```

## Sources

- OSV: https://osv.dev/vulnerability/GHSA-3whf-vgf2-9w6g

---
From sbomify Insights: https://insights.sbomify.com/GHSA-3whf-vgf2-9w6g/
Summaries are generated and may contain mistakes; the official description above is the record.