Zcash Zebra CVE-2026-104435

Exploitation requires an attacker to construct a Zcash V5 transaction with more transparent inputs than transparent outputs, where at least one input is signed using SIGHASH_SINGLE (alone or combined with ANYONECANPAY) and has no transparent output at the same index, then broadcast it so a vulnerable Zebra node validates it. No authentication is required (PR:N) and no non-default Zebra configuration is needed - default Zebra 4.4.0 / zebra-script 6.0.0 nodes are affected. The key LIMITING factor is that the consensus-split impact only materializes in a heterogeneous network where both Zebra and zcashd nodes operate; per the vendor, impact is currently mitigated because most miners run zcashd, and the CVSS AT:P metric reflects this network-mix precondition being outside the attacker's control.

This is a genuine integrity/availability risk for Zcash network operators running Zebra, but its real-world urgency is tempered by several signals. The provided CVSS 4.0 score is 8.3 (High) with vector AV:N/AC:L/AT:P/PR:N/UI:N and vulnerable-system impact VI:H/VA:H, VC:N - meaning no confidentiality loss, but high integrity (Zebra accepts a transaction that violates ZIP-244 consensus) and high availability impact (network partitioning / service disruption, and the advisory's claimed potential for double-spend). The AT:P metric reflects that exploitation depends on conditions outside the attacker's full control - specifically a mixed network of Zebra and zcashd nodes. Critically, the vendor advisory itself notes the impact is 'currently alleviated by the fact that most miners run zcashd,' which materially lowers practical risk today. There is no EPSS score in the provided data (MISSING), the CVE is NOT in CISA KEV, and no public exploit code is referenced, so exploitation status is 'no public exploit identified at time of analysis.' Conclusion: a real, patch-worthy consensus bug that Zebra operators should remediate promptly, but not a widely-weaponized emergency - real-world blast radius is constrained by Zebra's minority deployment and the zcashd-majority mining base. EPSS absence means probabilistic exploitation likelihood could not be cross-checked against the CVSS/KEV signals.

A remote, unauthenticated attacker crafts a V5 Zcash transaction containing more transparent inputs than outputs, where an input is signed with SIGHASH_SINGLE but has no transparent output at the same index, then broadcasts it to the network. Zebra 4.4.0 / zebra-script 6.0.0 computes a well-defined sighash over an empty output set and accepts the transaction, while zcashd correctly rejects it, driving the two node populations onto divergent views of valid state. No public exploit code is referenced, but the condition is straightforward to construct given documented ZIP-244 semantics.