Zcash Zebra CVE-2026-104430

No authentication or user interaction is required (PR:N/UI:N): any default Zebra 4.5.0 / zebra-script 7.0.0 node following the chain is affected simply by validating a block containing the crafted spends. The specific trigger is a P2SH redeem script whose CHECKMULTISIG is preceded by OP_1 through OP_16 (low-threshold multisig), which Zebra counts in legacy mode as 20 sigops. The practical limiting factor is that the crafted transaction must actually be mined into a block that zcashd accepts - the attacker broadcasts the spends but relies on block production to deliver the divergent block; no special Zebra configuration is needed, so all nodes on the vulnerable versions are exposed.

All impact signals point to availability of consensus-following, not confidentiality or integrity: the CVSS 4.0 vector (AV:N/AC:L/AT:N/PR:N/UI:N) with VC:N/VI:N/VA:H and base score 8.7 describes an unauthenticated, network-reachable, low-complexity availability attack. Zebra's zebra-script sigop counter uses legacy sigop counting for P2SH redeem scripts instead of zcashd's accurate P2SH mode, so a CHECKMULTISIG preceded by OP_1..OP_16 is overcounted as 20 sigops; an attacker can therefore craft a block that zcashd (the reference implementation holding consensus majority) accepts but Zebra rejects for exceeding MAX_BLOCK_SIGOPS, forking Zebra nodes off the canonical chain. There is no KEV listing and no EPSS score or public POC in the provided data, so this is no public exploit identified at time of analysis - but the bug is deterministic and cheaply triggerable once a crafted transaction is mined, so the practical barrier is low. The main risk qualifier is deployment scope rather than exploit difficulty: this is a consensus-divergence defect in one of two Zcash node implementations, a genuine patch-now priority for Zebra operators but not a broad-internet mass-exploitation event. Note the input Tags label this 'Information Disclosure', which conflicts with the VA:H / VC:N vector - the real impact is denial of service via consensus split, not disclosure.

An attacker constructs P2SH spends using low-threshold multisig redeem scripts (CHECKMULTISIG preceded by OP_1 through OP_16) and broadcasts them so they are mined into a block that zcashd validates as having an acceptable sigop count. Because Zebra overcounts each such operation as 20 sigops, that same block exceeds Zebra's MAX_BLOCK_SIGOPS and is rejected, stalling Zebra nodes off the chain while zcashd nodes continue. No public exploit code is identified at time of analysis, but no special privileges or user interaction are required (PR:N/UI:N).