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GHSA-3WHF-VGF2-9W6G

Vulnerability from github – Published: 2026-07-31 19:49 – Updated: 2026-07-31 19:49
VLAI
Summary
zaino-state has a Non-Finalized State Reorg — No Cycle Detection or Depth Limit
Details

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

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

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.
Severity
6.9 (Medium)
CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:L/SC:N/SI:N/SA:N
Show details on source website
To clipboard 

{
  "affected": [
    {
      "package": {
        "ecosystem": "crates.io",
        "name": "zaino-state"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            },
            {
              "fixed": "0.4.1"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "aliases": [],
  "database_specific": {
    "cwe_ids": [
      "CWE-770"
    ],
    "github_reviewed": true,
    "github_reviewed_at": "2026-07-31T19:49:35Z",
    "nvd_published_at": null,
    "severity": "MODERATE"
  },
  "details": "### Summary\n`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.\n\n### Details\n\n**Location:** `packages/zaino-state/src/chain_index/non_finalised_state.rs:443-489`\n\n```rust\nasync fn handle_reorg(\n    \u0026self,\n    working_snapshot: \u0026mut NonfinalizedBlockCacheSnapshot,\n    block: \u0026impl Block,\n) -\u003e Result\u003cIndexedBlock, SyncError\u003e {\n    let prev_block = match working_snapshot\n        .get_block_by_hash_bytes_in_serialized_order(block.prev_hash_bytes_serialized_order())\n        .cloned()\n    {\n        Some(prev_block) =\u003e {\n            if !working_snapshot\n                .heights_to_hashes\n                .values()\n                .any(|hash| hash == prev_block.hash())\n            {\n                Box::pin(self.handle_reorg(working_snapshot, \u0026prev_block)).await?  // \u003c-- LINE 459\n            } else {\n                prev_block\n            }\n        }\n        None =\u003e {\n            let prev_block = self\n                .source\n                .get_block(HashOrHeight::Hash(\n                    zebra_chain::block::Hash::from_bytes_in_serialized_order(\n                        block.prev_hash_bytes_serialized_order(),\n                    ),\n                ))\n                .await\n                .map_err(|e| { ... })?\n                .ok_or(SyncError::ValidatorConnectionError(...))?;\n            Box::pin(self.handle_reorg(working_snapshot, \u0026*prev_block)).await?  // \u003c-- LINE 483\n        }\n    };\n    let indexed_block = block.to_indexed_block(\u0026prev_block, self).await?;\n    working_snapshot.add_block_new_chaintip(indexed_block.clone());\n    Ok(indexed_block)\n}\n```\n\n**Infinite loop via self-referencing block:**\n1. A compromised validator serves a block `B` where `B.prev_hash == B.hash`.\n2. `handle_reorg` is called with `B`.\n3. `get_block_by_hash_bytes_in_serialized_order(B.prev_hash)` finds `B` itself in `working_snapshot.blocks`.\n4. Check: is `B.hash` in `working_snapshot.heights_to_hashes`? If `B` is a new chaintip not yet on the main chain, **no**.\n5. Recurse with `prev_block` = `B` (the exact same block).\n6. This repeats forever. The async recursion builds a new `Box::pin` future each iteration, consuming heap memory and CPU.\n\n**Stack exhaustion via deep reorg:**\nA deep reorg of \u003e1000 blocks would recurse \u003e1000 times. Each async recursion creates a new `Box::pin` future on the heap. While this won\u0027t exhaust the native stack immediately, it will allocate unbounded heap memory and CPU time, effectively DoS-ing the sync task.\n\n**`.expect(\"empty snapshot impossible\")` panic:**\n\n**Location:** `packages/zaino-state/src/chain_index/non_finalised_state.rs:543-548`\n\n```rust\nnew_snapshot.remove_finalized_blocks(finalized_height);\nlet best_block = \u0026new_snapshot\n    .blocks\n    .values()\n    .max_by_key(|block| block.chainwork())\n    .cloned()\n    .expect(\"empty snapshot impossible\"); // \u003c-- LINE 548\n```\n\nIf `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.\n\n### PoC\n\n1. Run a regtest.\n2. Serve a block where `header.previous_block_hash == block.hash()`.\n3. Zaino\u0027s `NonFinalizedState::sync` enters `handle_reorg` and infinite-loops.\n4. Sync never completes. CPU usage pegs to 100%. No new blocks are served to clients.\n\n### Fix\n\n1. **Add an explicit recursion depth limit** (e.g., max 1000 iterations) and return `SyncError::ReorgFailure` if exceeded:\n   ```rust\n   const MAX_REORG_DEPTH: usize = 1000;\n   ```\n2. **Track visited hashes** in a `HashSet\u003cBlockHash\u003e` during traversal to detect cycles and abort with an error.\n3. **Replace `.expect(\"empty snapshot impossible\")`** with a proper `Err(UpdateError::DatabaseHole)` or similar error return.\n\n### Additional Attack Vectors\n\n- **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.\n- **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.",
  "id": "GHSA-3whf-vgf2-9w6g",
  "modified": "2026-07-31T19:49:35Z",
  "published": "2026-07-31T19:49:35Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/zingolabs/zaino/security/advisories/GHSA-3whf-vgf2-9w6g"
    },
    {
      "type": "WEB",
      "url": "https://github.com/zingolabs/zaino/pull/1172"
    },
    {
      "type": "WEB",
      "url": "https://github.com/zingolabs/zaino/commit/428822509bc722eb9727681752686ede9bc87e77"
    },
    {
      "type": "WEB",
      "url": "https://github.com/zingolabs/zaino/commit/d874295f1377bec7fd712ef75b364181b8c77d46"
    },
    {
      "type": "WEB",
      "url": "https://github.com/zingolabs/zaino/commit/e05112aac54ec3cdb6da29fbc143ea710b32f009"
    },
    {
      "type": "PACKAGE",
      "url": "https://github.com/zingolabs/zaino"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:L/SC:N/SI:N/SA:N",
      "type": "CVSS_V4"
    }
  ],
  "summary": "zaino-state has a Non-Finalized State Reorg \u2014 No Cycle Detection or Depth Limit"
}



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