GHSA-443G-GWGP-49X4
Vulnerability from github – Published: 2026-07-02 19:34 – Updated: 2026-07-02 19:34Am I affected
You are affected if:
- You run
zebradup to and includingv4.4.1. - 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. Downstream CPU/blocking-pool impact analysis contributed by @ouicate.
{
"affected": [
{
"package": {
"ecosystem": "crates.io",
"name": "zebrad"
},
"ranges": [
{
"events": [
{
"introduced": "0"
},
{
"fixed": "4.5.0"
}
],
"type": "ECOSYSTEM"
}
]
},
{
"package": {
"ecosystem": "crates.io",
"name": "zebra-chain"
},
"ranges": [
{
"events": [
{
"introduced": "0"
},
{
"fixed": "8.0.0"
}
],
"type": "ECOSYSTEM"
}
]
}
],
"aliases": [],
"database_specific": {
"cwe_ids": [
"CWE-770"
],
"github_reviewed": true,
"github_reviewed_at": "2026-07-02T19:34:21Z",
"nvd_published_at": null,
"severity": "LOW"
},
"details": "### Am I affected\n\nYou are affected if:\n\n1. You run `zebrad` up to and including `v4.4.1`.\n2. Your node accepts inbound P2P connections.\n\n### Summary\n\nThe `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\u0027s `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.\n\nA single maximally-sized `getblocks` message occupies one blocking-pool thread for approximately 10\u201365ms. Under sustained load from multiple peers, this can degrade state-read performance for block validation, RPC, and mempool lookups.\n\n### Details\n\nThe `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.\n\nA legitimate block locator is logarithmic in chain length (approximately 30 hashes for the current ~3M-block Zcash chain). Zebra\u0027s own send-side cap is `MAX_FIND_BLOCK_HASHES_RESULTS = 500`.\n\nThe 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.\n\n### Patches\n\nPatched in Zebra 4.4.2. The fix caps `block::Hash::max_allocation()` at `MAX_BLOCK_LOCATOR_LENGTH = 101`, matching zcashd\u0027s `MAX_LOCATOR_SZ`. This causes the deserializer to reject oversized locators before any allocation or iteration occurs.\n\n### Workarounds\n\nNo specific workaround is needed. Existing backpressure mechanisms (load shedding, sequential per-peer message processing, connection limits) constrain the practical impact.\n\n### Impact\n\nUnder 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.\n\n### Credit\n\nVulnerability 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`.",
"id": "GHSA-443g-gwgp-49x4",
"modified": "2026-07-02T19:34:21Z",
"published": "2026-07-02T19:34:21Z",
"references": [
{
"type": "WEB",
"url": "https://github.com/ZcashFoundation/zebra/security/advisories/GHSA-443g-gwgp-49x4"
},
{
"type": "WEB",
"url": "https://github.com/ZcashFoundation/zebra/pull/10570"
},
{
"type": "WEB",
"url": "https://github.com/ZcashFoundation/zebra/commit/8981a1b95d4807cad99e5bb3b94fc8bc723ac033"
},
{
"type": "PACKAGE",
"url": "https://github.com/ZcashFoundation/zebra"
}
],
"schema_version": "1.4.0",
"severity": [
{
"score": "CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:L",
"type": "CVSS_V3"
}
],
"summary": "zebrad vulnerable to getblocks/getheaders locator CPU amplification via uncapped vector length"
}
Sightings
| Author | Source | Type | Date | Other |
|---|
Nomenclature
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- Patched: The vulnerability was observed as successfully patched by the user who reported the sighting.
- Not exploited: The vulnerability was not observed as exploited by the user who reported the sighting.
- Not confirmed: The user expressed doubt about the validity of the vulnerability.
- Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.
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