CVE-2026-34377 — zebrad
CVE-2026-34377 is a CWE-347 vulnerability in zebrad. A fix is available for zebrad — see the affected versions and patch details below.
Zebra has a Consensus Failure due to Improper Verification of V5 Transactions
Exploitation Status
No confirmed exploitation observed yet
- CISA’s own triage has not observed active exploitation or public proof-of-concept code for this CVE as of its last assessment.
Exploitation and automatability from CISA’s SSVC triage for CVE-2026-34377.
EPSS Exploitation Probability
EPSS (Exploit Prediction Scoring System) is a daily probability model maintained by FIRST.org. It estimates the likelihood a CVE will be exploited in production environments within the next 30 days, derived from real-world threat intelligence signals.
Real-World Exposure
zebrad🦀zebra-consensusReal-time download stats are indexed for npm and PyPI packages. This vulnerability affects crates.io packages — download data is not available via public APIs for these ecosystems.
Description
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 find_verified_unmined_tx 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 check_v5_auth() call for the transaction version provided in the block.
An attacker (specifically a malicious miner) could exploit this by:
- Observing a valid V5 transaction broadcast to the network and entering a Zebra node's mempool.
- Creating a block containing a modified version of that transaction. The modified version has the same
txidbut contains invalid signatures or proofs. - The affected Zebra node identifies the
txidin its mempool and incorrectly assumes the block's version of the transaction is already verified. - The node commits the block with the invalid transaction data.
- Other nodes (like
zcashdorzebranodes 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
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 🦀crates.io | zebrad | all versions | 4.3.0cargo update -p zebrad --precise 4.3.0 |
| 🦀crates.io | zebra-consensus | all versions | 5.0.1cargo update -p zebra-consensus --precise 5.0.1 |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for zebrad, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update zebrad to 4.3.0 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-34377 is resolved across your whole dependency graph.
Workarounds
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.
How O3 protects you
O3 Security's impact-aware SCA analyses which vulnerable code paths your application actually calls, so a match like CVE-2026-34377 can be triaged on real exposure rather than presence alone.
Tailored to CVE-2026-34377. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.
Frequently Asked Questions
Is CVE-2026-34377 in your dependencies?
O3 Security finds CVE-2026-34377 across crates.io dependencies, including transitive ones, and its impact-aware SCA ranks findings by whether your code actually calls the vulnerable path.