ZEBRA is a Zcash node written entirely in Rust. From zebrad versions 2.2.0 to before 4.3.1 and from zebra-rpc versions 1.0.0-beta.45 to before 6.0.2, a vulnerability in Zebra's JSON-RPC HTTP middleware allows an authenticated RPC client to cause a Zebra node to crash by disconnecting before the request body is fully received. The node treats the failure to read the HTTP request body as an unrecoverable error and aborts the process instead of returning an error response. This issue has been patched in zebrad version 4.3.1 and zebra-rpc version 6.0.2.

ZEBRA is a Zcash node written entirely in Rust. Prior to zebrad version 4.3.1 and prior to zebra-chain version 6.0.2, Orchard transactions contain a rk field which is a randomized validating key and also an elliptic curve point. The Zcash specification allows the field to be the identity (a "zero" value), however, the orchard crate which is used to verify Orchard proofs would panic when fed a rk with the identity value. Thus an attacker could send a crafted transaction that would make a Zebra node crash. This issue has been patched in zebrad version 4.3.1 and zebra-chain version 6.0.2.

ZEBRA is a Zcash node written entirely in Rust. Prior to zebrad version 4.3.1 and prior to zebra-script version 5.0.2, after a refactoring, Zebra failed to validate a consensus rule that restricted the possible values of sighash hash types for V5 transactions which were enabled in the NU5 network upgrade. Zebra nodes could thus accept and eventually mine a block that would be considered invalid by zcashd nodes, creating a consensus split between Zebra and zcashd nodes. In a similar vein, for V4 transactions, Zebra mistakenly used the "canonical" hash type when computing the sighash while zcashd (correctly per the spec) uses the raw value, which could also crate a consensus split. This issue has been patched in zebrad version 4.3.1 and zebra-script version 5.0.2.

CVE-2026-44497: Consensus Divergence in Transparent Sighash Hash-Type Handling due to Stale Buffer

Summary

The fix for https://github.com/ZcashFoundation/zebra/security/advisories/GHSA-8m29-fpq5-89jj introduced a separate issue due to insuficient error handling of the case where the sighash type is invalid, during sighash computation. Instead of returning an error, the normal flow would resume, and the input sighash buffer would be left untouched. In scenarios where a previous signature validation could leave a valid sighash in the buffer, an invalid hash-type could be incorrectly accepted, which would create a consensus split between Zebra and zcashd nodes.

Severity

Critical - This is a Consensus Vulnerability that could allow a malicious party to induce network partitioning, service disruption, and potential double-spend attacks against affected nodes.

Note that the impact is currently alleviated by the fact that currently most miners run zcashd.

Affected Versions

Zebra 4.3.1.

Description

Verification of transparent transactions inherits the Bitcoin Script verification code in C++, called from Zebra through a foreign function interface (FFI) with a Rust callback that computes the sighash. The fix for https://github.com/ZcashFoundation/zebra/security/advisories/GHSA-8m29-fpq5-89jj added the missing V5 hash-type consensus check on the Rust side, returning None for undefined hash types. However, the FFI bridge only writes to the C++ sighash buffer when the callback returns Some, and the C++ checker reads that buffer unconditionally, so the failure signal is lost.

An attacker could exploit this by:

- Constructing a transparent output spent by a script that runs a valid OPCHECKSIGVERIFY immediately before an OPCHECKSIG with an undefined hash type. - The first opcode primes the C++ sighash buffer with a valid digest; the second causes Zebra's callback to return None while the C++ checker verifies the invalid signature against the stale digest. - Zebra accepts the spend, zcashd rejects it, creating a consensus split in the network.

Impact

Consensus Failure

- Attack Vector: Network. - Effect: Network partition/consensus split. - Scope: Any affected Zebra node, and any miner or template pipeline that relies on Zebra's validation result.

Fixed Versions

This issue is fixed in 4.4.0.

The fixes uses a workaround where the input buffer is filled with random bytes on validation failure, which makes signature validation fail (as expected) with overwhelming probability. This avoids a breaking release of the zcashscript crate. A future release will propagate the error correctly for a direct fix.

Mitigation

Users should upgrade to 4.4.0 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.

Credits

Zebra thanks @sangsoo-osec for finding and reporting the issue.

CVE-2026-44500: Allocation Amplification in Inbound Network Deserializers

Summary

Several inbound deserialization paths in Zebra allocated buffers sized against generic transport or block-size ceilings before the tighter protocol or consensus limits were enforced. An unauthenticated or post-handshake peer could therefore force the node to preallocate and parse for orders of magnitude more data than the protocol intended, across headers messages, equihash solutions in block headers, Sapling spend vectors in V5/V4 transactions, and coinbase script bytes in blocks.

Severity

Moderate - This is a Denial-of-Service Vulnerability that could allow a malicious peer to amplify per-message memory and parse cost on Zebra nodes, with effects amplified by multi-peer fan-in.

Each individual case is bounded by the 2 MiB transport ceiling or the block-size cap, so no single message causes unbounded allocation, but the cumulative gap between intended and actual limits is significant.

Affected Versions

All Zebra versions prior to 4.4.0.

Description

Zebra's network codec uses TrustedPreallocate and generic Vec deserialization to bound inbound message parsing. In several places the bound used at the deserializer was the generic transport or block-size ceiling rather than the tighter protocol or consensus rule that applies to the field, so allocation happened first and the real limit was only enforced afterwards. Four such cases were identified:

- headers message receive cap. readheaders() deserialized the CountedHeader vector via the generic TrustedPreallocate path, which allowed up to ~1,409 entries per message. The protocol ceiling MAXFINDBLOCKHEADERSRESULTS = 160 was only used on the send side, giving an ~8.8x preallocation gap on receive. Reachable before the version handshake completes since the codec is installed on raw bytes. - Equihash solution length. Solution::zcashdeserialize decoded the solution as a generic Vec<u8> and only checked the exact consensus size (1344 bytes mainnet/testnet, 36 bytes regtest) afterwards in Solution::frombytes. A single fixed-size header field could be inflated to nearly the full block-size ceiling before rejection. - Sapling spend vectors in coinbase transactions. V5 spendprefixes and V4 shieldedspends were allocated generically with block-size-derived ceilings (~5,681 / ~5,208 entries) before the consensus rule that coinbase transactions have zero Sapling spends was enforced in the verifier. - Coinbase script bytes. Input::zcashdeserialize() read the coinbase script as a generic Vec<u8> up to the message-size cap before enforcing the consensus rule that coinbase scripts are between 2 and 100 bytes.

An attacker could exploit this by:

- Opening an inbound TCP connection (and, for the latter three cases, completing the version handshake). - Sending one of: a headers message with a CompactSize count up to ~1,409, a block whose header carries an inflated equihash CompactSize, a tx declaring a coinbase input with a large nSpendsSapling, or a block with a coinbase input whose script length is near the message-size ceiling. - The deserializer allocates against the loose ceiling, parses, and only then rejects.

Impact

Denial of Service

- Attack Vector: Network. - Effect: Amplified per-message allocation and parse cost on inbound peer messages, stackable across concurrent connections. The concrete effect will be influenced by how much memory Zebra has available. - Scope: Any affected Zebra node.

Fixed Versions

This issue is fixed in Zebra 4.4.0.

Mitigation

Users should upgrade to Zebra 4.4.0 or later immediately.

There are no known workarounds for this issue. Immediate upgrade is the only way to remove the amplified allocation surface on inbound peer messages.

Credits

Zebra thanks @Zk-nd3r for finding and reporting the issues.

ZEBRA is a Zcash node written entirely in Rust. Prior to version 4.4.0, Zebra's block validator undercounts transparent signature operations against the 20000-sigop block limit (MAXBLOCKSIGOPS), allowing it to accept blocks that zcashd rejects with bad-blk-sigops. A miner who produces such a block can split the network: Zebra nodes follow the offending chain while zcashd nodes do not. This issue has been patched in version 4.4.0.

CVE-2026-40881: addr/addrv2 Deserialization Resource Exhaustion

Summary

When deserializing addr or addrv2 messages, which contain vectors of addresses, Zebra would fully deserialize them up to a maximum length (over 233,000) that was derived from the 2 MiB message size limit. This is much larger than the actual limit of 1,000 messages from the specification. Zebra would eventually check that limit but, at that point, the memory for the larger vector was already allocated. An attacker could cause out-of-memory aborts in Zebra by sending multiple such messages over different connections.

Severity

Moderate - This is a Denial of Service Vulnerability that could allow an attacker to crash a Zebra node.

Affected Versions

All Zebra versions prior to version 4.3.1.

Description

The vulnerability exists in the readaddr/addrv2 functions in codec.rs. It deserializes a vector of addresses with the zcashdeserialize() trait method, which uses as a upper bound the result of T::maxallocation(). For theses types, it was derived from dividing the max message size (2 MiB) by the minimum serialized size of one entry. For AddrV1: 2097152 / 30 = 69,904. For AddrV2: 2097152 / 9 = 233,016. Only after deserialization was the MAXADDRSINMESSAGE = 1000 limit checked.

An attacker could exploit this by: 1. Creating addr or addrv2 messages with a large number of entries. 2. Submitting them to a Zebra node, possibly through multiple connections, to attempt to get Zebra into an out-of-memory state.

Impact

Denial of Service

Attack Vector: Network. Effect: Zebra node crash. Scope: Any impacted Zebra node.

Fixed Versions

This issue is fixed in Zebra 4.3.1.

The fix changes the maxallocation() method for the relevant types to return 1,000, thus blocking larger values prior to deserialization.

Mitigation

Users should upgrade to Zebra 4.3.1 or later immediately.

There are no known workarounds for this issue. Immediate upgrade is the only way to ensure the node remains not vulnerable to the denial of service attack.

Credits

Thanks @Zk-nd3r for finding and reporting the issue, and suggesting the fix.

CVE-2026-40880: Cached Mempool Verification Bypasses Consensus Rules for Ahead-of-Tip Blocks

Summary

A logic error in Zebra's transaction verification cache could allow a malicious miner to induce a consensus split. By carefully submitting a transaction that is valid for height H+1 but invalid for H+2 and then mining that transaction in a block at height H+2, a miner could cause vulnerable Zebra nodes to accept an invalid block, leading to a consensus split from the rest of the Zcash network.

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 prior to version 4.3.1. (Some older versions are not affected but are no longer supported by the network)

Description

The vulnerability exists due to a performance optimization whose goal is to improve performance of transaction validation if the transaction was previously accepted into the mempool (and thus was verified as valid). That however did not take into account that a transaction can be valid for a specific height, but invalid at higher heights; for example, it can contain an expiry height, a lock time, and it is always bound to a network upgrade, all of which are height-dependant.

An attacker (specifically a malicious miner) could exploit this by (e.g. in the expiry height case):

- Submitting a transaction with expiry height H+1 (where H is the height of the current tip) - Mining a block H+1, and a block H+2 that contains that same transaction, and submitting block H+2 before H+1 - Zebra nodes would accept H+2 as valid (pending contextual verification) and wait for block H+1; when it arrives, Zebra would commit both blocks even if H+2 contains an expired transaction - Other nodes (like zcashd or zebrad 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 4.3.1.

We removed the performance optimization altogether, since we deemed it too risky.

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.

Credits

Thanks to @sangsoo-osec for a thorough advisory submission that noticed the lock time issue, and to @shieldedonly with an also thorough advisory (that was submitted while we were working on the first one) who noticed that the issue applied to other aspects of the transaction validation.

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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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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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