Zebra Node Uncontrolled Resource Consumption via Forged Block Bodies

Executive Summary

Zebra before version 6.4.0 has an uncontrolled resource consumption flaw. Unauthenticated peers can exploit this by sending forged block bodies with valid header hashes, forcing full proof verification. Attackers manipulate authorizing-only bytes like a coinbase scriptSig, wasting proof verification resources for Sapling, Orchard, and Ironwood without consequences. This causes sync stalls of up to 67 seconds.

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Detection Guidance

Monitor Zebra node logs for repeated full proof verifications or sync stalls. Check for peers sending blocks with mismatched authorizing data despite valid header hashes. Use network monitoring tools to detect unusual inbound connections or traffic patterns targeting Zebra nodes.

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Impact Analysis

This vulnerability can stall Zcash node synchronization for extended periods, reducing network reliability and performance. Users running vulnerable Zebra versions may experience delays in transaction processing and block validation, potentially disrupting services dependent on timely data.

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Compliance Impact

This vulnerability primarily impacts system availability by causing resource exhaustion through forced proof verification, which could lead to service disruptions. It does not directly affect data confidentiality or integrity, so direct impacts on GDPR or HIPAA compliance may be limited unless availability is a critical requirement for those standards.

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Mitigation Strategies

Upgrade Zebra to version 6.4.0 or later to address the uncontrolled resource consumption vulnerability. Monitor network traffic for unusual proof verification requests that may indicate exploitation attempts.

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