CVE-2026-104428 in Zebra
Summary
by MITRE • 10/02/2026
The getblock RPC method in zebra-rpc before 11.0.0, used by the Zcash Foundation's Zebra node, panics on verbosity 2 for a side-chain block because the block's -1 confirmations sentinel is converted to u32 with .expect(), aborting the process. Remote unauthenticated attackers, directly or through lightwalletd, can repeat this call to keep the node in a crash loop.
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Analysis
by VulDB Data Team • 10/02/2026
The vulnerability identified within the zebra-rpc component of Zebra nodes prior to version 11.0.0 represents a critical denial-of-service condition stemming from improper handling of integer data types during block validation and reporting processes. Specifically, the getblock RPC method exhibits a flaw when processing side-chain blocks with verbosity level set to two. In this specific operational context, the software attempts to convert a confirmation count value that is represented as negative one into an unsigned 32-bit integer using the Rust expect() function. This conversion operation triggers a panic because negative values cannot be accurately represented in unsigned integer formats, leading directly to process termination rather than graceful error handling or data sanitization.
From a technical perspective, this issue classifies under CWE-190 Integer Overflow or Wraparound and CWE-754 Improper Check for Unusual or Exceptional Conditions. The root cause lies in the assumption that confirmation counts will always be non-negative values suitable for unsigned integer storage without prior validation of their sign status. When a side-chain block is queried, its lack of confirmations on the main chain results in a sentinel value of negative one being passed to the conversion routine. Because the code relies on expect() rather than safe arithmetic operations or explicit type checking with error propagation, any attempt to access this specific data structure causes an immediate abort of the node process. This behavior violates fundamental principles of robust software engineering where external inputs and internal state variables must be validated before critical type conversions occur.
The operational impact of this vulnerability is severe for network participants running affected Zebra nodes. Remote unauthenticated attackers can exploit this flaw by sending a specifically crafted RPC request with verbosity set to two targeting side-chain blocks. Since the attack does not require authentication, any node exposing its RPC interface to the public internet or even local networks becomes susceptible. The attacker can repeatedly send these malicious requests, causing the Zebra node to crash and restart in an endless loop. This denial-of-service condition effectively removes the node from the network, reducing overall hash rate availability and potentially impacting the reliability of block propagation for other peers relying on that specific node for synchronization or data retrieval services.
Mitigation strategies primarily involve upgrading the zebra-rpc component to version 11.0.0 or later where this integer conversion logic has been corrected to handle negative confirmation counts appropriately, likely by using signed integers or implementing explicit checks before type casting. In environments where immediate patching is not feasible, network administrators should restrict access to RPC endpoints through firewall rules or reverse proxies that filter out requests with verbosity level two for side-chain block queries until the software update can be applied. Additionally, deploying monitoring solutions that detect repeated crashes of the Zebra process can help identify active exploitation attempts and trigger automated restarts while maintaining awareness of ongoing attacks against infrastructure integrity.