PT-2026-55472 · Crates.Io · Zebra-State+1

Published

2026-07-02

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Updated

2026-07-02

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CVE-2026-52736

CVSS v4.0

8.7

High

VectorAV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:H/VA:N/SC:N/SI:N/SA:N

Description

Am I affected

You are affected if:
  1. You run any version of zebrad up to and including v4.4.1.
  2. Your node accepts inbound P2P connections (network.listen addr is set, which is the default).
  3. Your node processes blocks past the checkpoint height (non-finalized state is active).
All default configurations are affected.

Summary

Zebra records a block hash in non finalized block write sent hashes when the block is sent to the write task, before contextual validation completes. If validation fails, the hash is not removed. A remote unauthenticated peer can deliver a poisoned block body that shares a header hash with a later valid canonical block. The poisoned body is rejected, but the hash remains cached. When the valid canonical block arrives, Zebra treats it as a duplicate and rejects it. The node cannot advance past that height until restart or a reorg event.

Details

ZIP-244 defines txid v5 without binding transparent input scriptSig, which lives in auth digest and is committed to by hashBlockCommitments in the block header. Because merkle root is computed over txids (not auth digests), and the block hash is computed over the header, an attacker can construct two blocks with identical header hashes but different transaction bodies by mutating the coinbase scriptSig.
The attack flow over P2P:
  1. Attacker observes a new block header (from any peer).
  2. Attacker constructs a poisoned body by flipping a byte of the coinbase scriptSig extra-data section. The block hash is unchanged.
  3. Attacker advertises the block hash via inv to the target node.
  4. Target requests the block via getdata; attacker serves the poisoned body.
  5. Zebra adds the hash to non finalized block write sent hashes before validation.
  6. The write task rejects the body at block commitment is valid for chain history (auth data root mismatch).
  7. The hash is not removed from non finalized block write sent hashes.
  8. When the valid canonical block arrives (from honest peers or RPC), queue and commit to non finalized state sees the hash in the cache and returns KnownBlock::WriteChannel duplicate.
  9. The node is stuck at height N-1.
A secondary variant exists where chain pruning (via MAX NON FINALIZED CHAIN FORKS) removes a chain from chain set but leaves its block hashes in non finalized block write sent hashes, producing the same lockout for children of the pruned fork.

Patches

Patched in Zebra 4.4.2. The fix removes stale entries from non finalized block write sent hashes on every failed non-finalized write path.

Workarounds

There is no complete configuration-level workaround. Reducing the node's inbound peer count (network.peerset initial target size) narrows the attack surface but does not eliminate it. Restarting the node clears the in-memory cache and allows the valid block to be re-fetched.

Impact

A remote unauthenticated P2P peer can permanently stall a targeted Zebra node at a specific block height. The node diverges from the network tip; downstream consumers (lightwalletd, wallets, explorers, mining infrastructure) relying on the node see a stalled chain. The attack requires winning a propagation race: delivering the poisoned block body before honest peers deliver the canonical block. A well-positioned attacker (low-latency connection to the target, observation of new blocks from other peers) can reliably win this race. In sustained form, the attacker repeats for each new block, keeping the target permanently behind.
Recovery requires restarting the node (which clears the in-memory sent-hash cache) or waiting for a reorg at the affected height (rare on the canonical chain).

Credit

Reported independently by @ipwning (primary, with ZIP-244 malleability analysis and zcashd cross-reference) and @x15-eth (first reporter, with E2E reproduction and control experiment).

Fix

Found an issue in the description? Have something to add? Feel free to write us 👾
dbugs@ptsecurity.com

Weakness Enumeration

CWE-459

Related Identifiers

CVE-2026-52736
GHSA-4M69-67M6-PRQP

Affected Products

Zebra-State
Zebrad