---
id: GHSA-443g-gwgp-49x4
title: >-
  zebrad vulnerable to getblocks/getheaders locator CPU amplification via
  uncapped vector length
summary: >-
  zebrad vulnerable to getblocks/getheaders locator CPU amplification via
  uncapped vector length
severity: low
cvss: 3.7
cwe:
  - CWE-770
vendor: zebrad
product: zebrad
ecosystem: rust
affected:
  - zebrad < 4.5.0
  - zebra-chain < 8.0.0
patched:
  - zebrad 4.5.0
  - zebra-chain 8.0.0
published: '2026-07-02'
updated: '2026-07-02'
source: GHSA
sourceUrl: 'https://github.com/advisories/GHSA-443g-gwgp-49x4'
references:
  - url: >-
      https://github.com/ZcashFoundation/zebra/security/advisories/GHSA-443g-gwgp-49x4
  - url: 'https://github.com/ZcashFoundation/zebra/pull/10570'
  - url: >-
      https://github.com/ZcashFoundation/zebra/commit/8981a1b95d4807cad99e5bb3b94fc8bc723ac033
  - url: 'https://github.com/advisories/GHSA-443g-gwgp-49x4'
tags:
  - ghsa
  - rust
ingestedAt: '2026-07-02T19:41:50.924Z'
---

## Overview

### Am I affected

You are affected if:

1. You run `zebrad` up to and including `v4.4.1`.
2. Your node accepts inbound P2P connections.

### Summary

The `read_getblocks` and `read_getheaders` codec paths accepted block locator vectors up to approximately 65,535 entries (the generic `TrustedPreallocate` ceiling derived from `MAX_PROTOCOL_MESSAGE_LEN`), rather than the protocol-specification limit of 101 entries (matching zcashd's `MAX_LOCATOR_SZ`). Each entry in the locator vector triggers a per-hash chain lookup (`HashMap::contains_key` + `RocksDB::contains_hash`) in `find_chain_intersection` on a tokio blocking-pool thread.

A single maximally-sized `getblocks` message occupies one blocking-pool thread for approximately 10–65ms. Under sustained load from multiple peers, this can degrade state-read performance for block validation, RPC, and mempool lookups.

### Details

The `read_headers` codec path already implements the correct pattern: it reads the CompactSize count, validates against `MAX_HEADERS_PER_MESSAGE = 160` before deserialization, and rejects oversized messages. The `read_getblocks` and `read_getheaders` paths were missing this pre-deserialization count check and instead relied on the generic `block::Hash::max_allocation()` bound, which allows `(MAX_PROTOCOL_MESSAGE_LEN - 1) / 32 = 65,535` hashes.

A legitimate block locator is logarithmic in chain length (approximately 30 hashes for the current ~3M-block Zcash chain). Zebra's own send-side cap is `MAX_FIND_BLOCK_HASHES_RESULTS = 500`.

The practical impact requires significant attacker bandwidth (approximately 2 MiB per request) and multiple Sybil peers to meaningfully degrade the blocking pool, which limits real-world exploitability.

### Patches

Patched in Zebra 4.4.2. The fix caps `block::Hash::max_allocation()` at `MAX_BLOCK_LOCATOR_LENGTH = 101`, matching zcashd's `MAX_LOCATOR_SZ`. This causes the deserializer to reject oversized locators before any allocation or iteration occurs.

### Workarounds

No specific workaround is needed. Existing backpressure mechanisms (load shedding, sequential per-peer message processing, connection limits) constrain the practical impact.

### Impact

Under sustained load from multiple Sybil peers, oversized locator vectors can occupy blocking-pool threads and degrade state-read performance. The effect is bounded by connection limits and requires significant attacker bandwidth.

### Credit

Vulnerability identified by `@dingledropper`, who submitted the fix in [PR #10570](https://github.com/ZcashFoundation/zebra/pull/10570). Downstream CPU/blocking-pool impact analysis contributed by `@ouicate`.

## Affected packages

- `zebrad < 4.5.0`
- `zebra-chain < 8.0.0`

## Remediation

Upgrade to a patched release:

- `zebrad 4.5.0`
- `zebra-chain 8.0.0`