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Remote Denial of Service via Crafted V5 Transactions
Summary A vulnerability in Zebra's transaction processing logic allows a remote, unauthenticated attacker to cause a Zebra node to panic (crash). This is triggered by sending a specially crafted V5 transaction that passes initial deserialization but fails during transaction ID calculation.
Severity Critical - This is a Remote Denial of Service (DoS) that requires no authentication and can be triggered by a single network message.
Affected Versions All Zebra versions supporting V5 transactions (Network Upgrade 5 and later) prior to version 4.3.0.
Description The vulnerability stems from Zebra lazily validating transaction fields that are eagerly validated in the librustzcash parsing logic used when Zebra computes transaction ids and auth digests for V5 transactions where Zebra panics if those computations fail.
PushTransaction messages with malformed V5 transactions are successfully deserialized as the zebra-chain Transaction type by the network codec, but when Zebra converts those transactions into internal types to compute the TxID expecting it to succeed, it triggers a panic/crash.
An attacker can trigger this crash by sending a single crafted tx message to a Zebra node's public P2P port. The same issue can be triggered via the sendrawtransaction RPC method.
Impact Remote Denial of Service Attack Vector: Remote, unauthenticated. Effect: Immediate crash of the Zebra node. Scope: Any node with an open P2P port (default 8233) or exposed RPC interface is vulnerable.
Fixed Versions This issue is fixed in Zebra 4.3.0.
The fix ensures that any transaction that would fail TxID calculation is rejected during the initial deserialization phase, and replaces internal panics with graceful error handling.
Mitigation Users should upgrade to Zebra 4.3.0 or later immediately.
If an immediate upgrade is not possible, users should ensure their RPC port is not exposed to the Internet. However, the P2P port must remain closed or restricted to trusted peers to fully mitigate the risk, which may impact the node's ability to sync with the network.
Credits Zebra thanks robustfengbin, who discovered this issue and reported it via coordinated disclosure process.
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CVE-2026-34377: Consensus Failure via Crafted V5 Authorization Data
Summary A logic error in Zebra's transaction verification cache could allow a malicious miner to induce a consensus split. By matching a valid transaction's txid while providing invalid authorization data, a miner could cause vulnerable Zebra nodes to accept an invalid block, leading to a consensus split from the rest of the Zcash network. To be clear, this would not allow invalid transactions to be accepted but could result in a consensus split between vulnerable Zebra nodes and invulnerable Zebra and Zcashd nodes.
Severity High - This is a Consensus Vulnerability that could allow a malicious miner to induce network partitioning, service disruption, and potential double-spend attacks against affected nodes.
Affected Versions All Zebra versions supporting V5 transactions (Network Upgrade 5 and later) prior to version 4.3.0.
Description The vulnerability exists in the findverifiedunminedtx function within transaction.rs. This function was designed to optimize block verification by checking if a transaction was already verified in the mempool.
The lookup mechanism used the ZIP-244 txid as the unique key. However, for V5 transactions, the txid specifically excludes the Authorization Data Root (signatures and proofs). Because Zebra returned a "verified" status based solely on the txid, it skipped the essential checkv5auth() call for the transaction version provided in the block.
An attacker (specifically a malicious miner) could exploit this by: 1. Observing a valid V5 transaction broadcast to the network and entering a Zebra node's mempool. 2. Creating a block containing a modified version of that transaction. The modified version has the same txid but contains invalid signatures or proofs. 3. The affected Zebra node identifies the txid in its mempool and incorrectly assumes the block's version of the transaction is already verified. 4. The node commits the block with the invalid transaction data. 5. Other nodes (like zcashd or zebra nodes without that transaction in their mempool) reject the block, resulting in a chain fork where the poisoned Zebra node is isolated.
Impact Consensus Failure Attack Vector: Network (specifically via a malicious miner). Effect: Network partition/consensus split. Scope: Any Zebra node utilizing the transaction verification cache optimization for V5 transactions.
Fixed Versions This issue is fixed in Zebra 4.3.0.
The fix ensures that verification is only skipped if the transaction's full integrity—including authorization data—is validated against the mempool entry.
Mitigation Users should upgrade to Zebra 4.3.0 or later immediately.
There are no known workarounds for this issue. Immediate upgrade is the only way to ensure the node remains on the correct consensus path and is protected against malicious chain forks.
Resources Zebra 4.3.0 Release Announcement ZIP-244: Transaction Identifier
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